Pub_Abstracts

ABSTRACTS

CSSS 1

Mechanically Assembled 3D Mesostructures as Scaffolds for Multifunctional Materials

J. Rogers. Northwestern University, Evanston, IL. Email: jrogers@northwestern.edu

A rapidly expanding area of research in materials science focuses on the development of routes to complex functional materials that exploit engineered three dimensional (3D) architectures. This talk summarizes recently developed strategies in geometric transformation that allow for the spontaneous, guided assembly of 3D mesostructures from two dimensional (2D) precursors, where the characteristic feature sizes can span the entire mesoscopic range, from tens of nanometers to hundreds of microns and more. A goal is to create scalable capabilities for defining properties of materials systems not only through the chemical compositions and morphological characteristics of their constituents but also through well-defined, static or tunable 3D configurations. The resulting systems can be viewed as metamaterials, where engineered mesostructures lead to unique and important optical, thermal, acoustic, mechanical and electronic properties. This presentation includes a broad range of such examples.

CSSS 2

Nanocolloids on the move

P. Fischer. Micro Nano and Molecular Systems, Max Planck Institute and Univ. of Stuttgart, Stuttgart, GERMANY. Email: fischer@is.mpg.de

The field of active and self-propelled micro- and nanomotors is seeing major advances. It encompasses externally as well as chemically propelled colloids, which serve as model systems for the emergence of self-organization and collective phenomena. A fascinating question is how symmetry-broken propulsion may arise from simple isotropic building blocks. It is shown that active colloids can self-assemble to self-propel, thus 'activity' can itself give rise to spontaneous symmetry breaking. In this talk I will also describe our work in fabricating large numbers of reactive hybrid colloids that can move through biomedically important media, as well as active nanocolloids that form active gels. It is discussed how active matter may be designed to move towards a chemical fuel, which would have far-reaching implications for nanomedicine.

CSSS 3

Encoding biomimetic 3D helical motion in microparticles: Finding new pathways for navigating complex environments

J. Lee, B. Bharti. Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA. Email: bbharti@lsu.edu

Active particles are colloids performing autonomous non-thermal motion in fluids. One such class of active particles are metallodielectric Janus spheres. In presence of an external electric field, a breakdown in the fluid-flow symmetry around the metallodielectric Janus particles drive their active motion. The motion of Janus particles in electric field remains linear and steering such particles along non-linear 3D trajectories remains a challenge. Here we will present experimental design principles of programming swimming force distribution on the surface of a colloidal particle and thus steering the particles along non-linear complex trajectories. The approach is based on designing the surface patch and particle shape that allows for coupling of force and torque components. We find that such coupling results into 3D helical motion of the active colloids, where the handedness is governed by the patch orientation in applied field. We will present the effect of patch size, shape and applied electric field on the active helical motion of the particles. We will also show that the helical trajectory of colloidal particles enable them to navigate through complex crosslinked environments. Our approach introduces a new method of programming dynamics of active colloids, which could lead to the development of advanced micromotors, miniature robots and non-equilibrium crystals with unusual response to external stresses.

CSSS 4

Chemical oscillation of micromotors drives reversible assembly of colloids

A. Altemose, A. Sen. Chemistry, Penn State, State College, PA. Email: asa5237@psu.edu

Self-organization is observed in many systems throughout nature, from the microscopic level of bacteria colonies to the macroscopic level of bird flocks, fish schools, and even human traffic patterns. The ability of individuals to maintain their independent behavior but also be a part of an organized group is one of the most interesting characteristics of life. With the discovery of artificial self-propelled particles at the microscale in the last decade, researchers have been studying the interactions of these synthetic microswimmers in search of the types of collective behavior seen in biological systems. Several artificial systems have been reported that demonstrate complex pattern formation and coordinated motion. Here, we demonstrate a system that exhibits chemical communication between active and inactive particles which drives the reversible assembly of colloidal crystals. More specifically, we report autonomous hexagonal packing of inert silica particles due to the oscillatory behavior of neighboring silver phosphate micromotors under UV light in hydrogen peroxide. In a previous study, we characterized the tunable oscillatory behavior of the silver phosphate micromotors, which follows a self-diffusiophoretic mechanism of alternating electric fields between individual motors. Here we use these active particles to induce colloidal crystallization in passive silica tracer particles. The crystalline formations of these tracers appear under UV illumination of the system and rapidly relax into a disordered state when the light is turned off. In addition, the crystals can reform and reconfigure with ease under UV light, as is seen when waves of spreading and condensing particle motion pass through the system periodically, caused by waves of alternating electric fields. In other words, the oscillatory nature of the active silver phosphate particles results in waves of crystallization and disorder propagating from cluster to cluster of passive particles, as shown in the attached figure. These oscillatory waves occasionally cause a smoothing of defects between crystal boundaries, a phenomenon which may lead to exciting applications in material assembly and optics.

CSSS 5

Active colloidal assemblies of metallo-dielectric microcubes: Self-reconfiguring microbots and self-propelling microswimmers

K. Han1, C. W. Shields IV2, B. Bharti3, G. P. Lpez4, O. D. Velev1. 1Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, 2Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 3Chemical Engineering, Louisiana State University, Baton Rouge, LA, 4Chemical and Biological Engineering, University of New Mexico, Albuquerque, NM. Email: khan4@ncsu.edu

A new class of dynamically and reversibly reconfigurable active colloidal clusters made by magnetic assembly and actuation of metallo-dielectric patchy microcubes will be presented. We describe how magnetically responsive patchy microcubes can be assembled into self-reconfiguring microclusters and employed as microbots and self-propelling swimmers. The key feature of these assemblies is that they can effectively store magnetic energy in the asymmetrically coated metallic patches in the form of interacting residual magnetic dipoles. As a result, on-demand dynamic reconfiguration of the assemblies can be achieved by switching between directional field-dipole and dipole-dipole interactions via turning the magnetic field on and off. The pattern of reconfiguration can be encoded in the sequence of the cube orientations within the assemblies. We provide examples of cube clusters of specific sequences that can be actuated to perform microscale operations such as capturing and transporting live cells, or acting as prototypes of self-reconfiguring microbots. We also note that these reconfigurable clusters can directionally move by self-viscophoresis, acting as a new class of self-propelling microswimmers, when suspended in non-Newtonian fluids and actuated by time-asymmetric magnetic fields. The origins of the propulsion of these clusters will be analyzed by a coupled scallops model for energy dissipation in the surrounding fluid.

CSSS 6

2D Colloidal clusters that beat like a heart or wrinkle like a brain

C. Zhou1, R. Dong2, S. Granick2, W. Wang1. 1School of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, CHINA, 2Center for Soft and Living Matter, Institute of Basic Science, Ulsan, KOREA, REPUBLIC OF. Email: weiwang_chem@126.com

Spatiotemporal patterns are a hallmark of dissipative systems and the presence of ordered competitions. These patterns are found over a wide range of length and time scales, including colored spirals in a BZ mixture, vesicles under osmotic shock, growth of metal fractal dendrites, and the cellular patterns in a shallow cylindrical flame, to name a few [1]. There is always a strong interest to produce spatiotemporal patterns in a laboratory setup, partly as a means to understand natural wonders, and arguably for the pure esthetic pleasure as well.Here we demonstrate two examples where the combination of external forces (acoustic radiation force) and particle-particle interactions give rise to dynamic and exotic behaviors, both at a single-particle level and collectively. In particular, the formed patterns carry superficial features of a beating heart or a wrinkled brain.The inspiration of the first example comes from a previous study by Ibele et al. [2] In our experiments, polymethylmethacrylate (PMMA) microspheres half coated with silver, when irradiated with light and in the presence of hydrogen peroxide (H2O2) and potassium chloride (KCl), start to move towards PMMA side in a pulsating manner. Interesting, when trapped by ultrasound into a cluster, the individual pulsation of active particles synchronizes with their neighbors, leading to a beating cluster that expand and contract in unison, much like a beating heart. Moreover, preliminary experiments show the possibility of neighboring clusters to gradually synchronize in beating, with the same beating frequency but a slightly shifted phase, possibly due to the propagation of a chemical wave.In the second example, a tightly (but not necessarily closely) packed cluster of polystyrene microspheres was formed by radial acoustic pressure. By applying an alternating current electric field vertical to the cluster plain while holding the ultrasound, the cluster rapidly expanded with wrinkles that developed over the entire cluster. The final result is a labyrinth structure similar to that of a phase separated diblock copolymer. We suspect the expansion of the wrinkled cluster is a result of the interplay between the inward acoustic force and the in-plan repulsive dipolar forces among dielectric particles. Although similar wrinkles or labyrinth structures have been previously reported for superparamagnetic microspheres [3] and granular beads [4], and were predicted for isotropic repulsive particles [5] and particles with short-range attractions and long-range repulsions [6], this is arguably the first demonstration of its appearance with electrically polarized colloids. In addition, under certain sets of parameters large wrinkles (i.e. of longer wavelength) immediately formed once the electric field was turned on, but quickly disappeared, giving way to finer wrinkles that persisted while the cluster continued to expand. Such an exotic development of patterns that is opposite to a spinodal decomposition is not fully understood at this point.Ref:1. Ball, P, The Self-made Tapestry: Pattern Formation in Nature, Oxford University Press, 19992. Ibele, M. E.; Lammert, P. E.; Crespi, V. H.; Sen, A. Emergent, Collective Oscillations of Self-Mobile Particles and Patterned Surfaces Under Redox Conditions. ACS Nano 2010, 4 (8), 48454851.3. Osterman, N.; Babi, D.; Poberaj, I.; Dobnikar, J.; Ziherl, P. Observation of Condensed Phases of Quasiplanar Core-Softened Colloids. Phys. Rev. Lett. 2007, 99 (24), 248301.4. Merminod, S.; Jamin, T.; Falcon, E.; Berhanu, M. Transition to a Labyrinthine Phase in a Driven Granular Medium. Phys. Rev. E 2015, 92 (6), 062205.5. Malescio, G.; Pellicane, G. Stripe Phases From Isotropic Repulsive Interactions. Nature 2003, 2 (2), 97100.6. Haw, M. D. Growth Kinetics of Colloidal Chains and Labyrinths. Phys. Rev. E 2010, 81 (3), 031402.

CSSS 7

Stimuli-Responsive and Nanostructured Polymer Films for Modulating Adhesion and Friction: Fabrications, Applications and Limitations

S. Giasson1, L. Giraud2. 1Chemistry and Pharmacy, Universite de Montreal, Montral, QC, CANADA, 2Pharmacy, Universite de Montreal, Montral, QC, CANADA. Email: suzanne.giasson@umontreal.ca

Whenever one material moves against another, some energy can be lost due to adhesion hysteris and/or friction. That energy is transferred into unwanted heat, deformation, or wear reducing the materials lifetime. A number of experimental studies have shown that polymer coatings can be efficiently used to control friction and adhesion between surfaces. Polymer coatings have properties and responsiveness that are contingent on the chemical composition, size and shape of structure, elasticity. However, they are generally suffering from major shortcomings such as lack of responsiveness selectivity and reversibility, poor environmental stability and limited understanding of the structure-function relationship, which are all critical to design reliable rules for building responsive or self-lubricating surfaces. Experimental surface forces studies of different classes of solvated polymer-bearing surfaces carried out using the surface forces apparatus and similar molecular techniques will be presented in order to elucidate the responsiveness mechanism and the structure-property relationship between polymer-coated surfaces in aqueous media. Eventhough conclusive understanding is still hampered by the difficulty of systematically controlling the polymer grafting density and conformation, the studies suggest that the effective lubrication mechanisms involve the facility with which macromolecules under compression remain hydrated and hold a significant amount of water at the surfaces to be lubricated.

CSSS 8

Proximity-induced changes in adsorption

P. Gaddam, R. Grayson, W. Ducker. Virginia Tech, Blacksburg, VA. Email: prudvi91@vt.edu

Abstract:We discuss whether adsorption in a thin aqueous film is a function of the thickness of the film. Adsorption as a function of film thickness has previously been considered for ions and is known as charge regulation. The more general case for surfactants, etc., is sometimes called proximal adsorption, and a general thermodynamic treatment was developed by Hall,1 and by Ash et al.2A key application is that, if adsorption should vary as a function of film thickness, then such proximal adsorption should be considered in calculating surface forces that determine colloidal stability. For example, proximal adsorption of a surfactant molecule could vary during the collision of two particles and this change in adsorption would result in a different force.In this presentation, we describe measurements of the adsorption of fluorescein from aqueous solution as a function of film thickness. Using fluorescence microscopy, we can directly measure the number of fluorescent ions as a function of film thickness. The film thickness is determined using interferometry. We show that the surface excess of fluorescein is a function of film thickness, and measure the proximal adsorption as a function of Debye-length. As far as we are aware, this is the first direct measurement of proximal adsorption. Results are compared to a simple calculation using the Poisson-Boltzmann equation.1. Hall, D. G. Thermodynamic Treatment of Some Factors Affecting the Interaction Between Colloidal Particles. J. Chem. Soc. Faraday Trans. II 1972, 68, 2169-2182.2. Ash, S. G.; Everett, D. H.; Radke, C. Thermodynamics of the Effects of Adsorption on Interparticle Forces. J. Chem. Soc. Faraday Trans. II 1972, 69, 1256-1277.

CSSS 9

Domain Expansion Dynamics and Nanoridge-to-Mesa Instability in Stratifying, Micellar Foam Films

V. Sharma, Y. Zhang. Chemical Engineering, University of Illinois at Chicago, Chicago, IL. Email: viveks@uic.edu

Ultrathin films exhibit stratification due to confinement-induced structuring and layering of small molecules in simple fluids, and of supramolecular structures like micelles, lipid layers and nanoparticles in complex fluids. Stratification proceeds by the formation and growth of thinner domains at the expense of surrounding thicker film, and flows and instabilities drive the formation of nanoscopic terraces, ridges and mesas within a film. The detailed mechanisms underlying stratification are still under debate, and are resolved in this contribution by addressing long-standing experimental and theoretical challenges. Thickness variations in stratifying films are visualized and analyzed using interferometry, digital imaging and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness < 100 nm, lateral ~500 nm) and temporal resolution (< 1 ms). Using IDIOM protocols, we characterize the shape and the growth dynamics of nanoridges and mesas that flank the expanding domains in micellar thin films. We show that topographical changes including ridge growth and instability, and the overall stratification dynamics, can be described quantitatively by nonlinear thin film equation, amended with supramolecular oscillatory surface forces. Often, due to a nanoridge-to-mesa instability, one or more brighter mesas appear at the circular moving front between thinner domains and the thicker (less dark) surrounding film. Quantitative analysis reveals that only mesas grow in size after the instability, whereas the rest of the nanoridge preserves shape. In analogy with phase separation into compositionally-distinct regions, we show that the spontaneous nucleation thicker mesas in stratifying films is a phase transitions driven by the oscillatory nature of free energy functional.

CSSS 10

Characterizing DNA-mediated interactions between colloidal particles and fluid membranes

S. Merminod, W. B. Rogers. Physics, Brandeis University, Waltham, MA. Email: smerminod@brandeis.edu

Binding of small particles (e.g. proteins, viruses, or colloids) to fluid membranes via ligand-receptor interactions can direct the self-organization of two-dimensional assemblies, as in the 'purple membrane' in Halobacteria. In this talk, I will present a model system for exploring the physical mechanisms leading to self-assembly of colloidal particles bound to interfaces. To start, we characterize the interactions between colloidal particles and a fluid surface. Specifically, we graft single-stranded DNA onto colloidal particles and into a supported lipid bilayer, so that hybridization of complementary DNA molecules generates an attractive, specific force between them. Using a custom-made total internal reflection microscope, we measure particle-surface attractions with kT-scale precision and the associated binding kinetics with high temporal resolution. We aim to explore how the strength, specificity, and dynamics of the interactions that emerge depend on the molecular attributes of the ligands and receptors. These experiments may help shed light on the self-assembly of small particles bound to membranes, and possibly the formation of complex membrane structures, such as the 'microribs in Morpho butterfly wings, which give them their brilliant coloration and iridescence.

CSSS 11

Dynamics of graphite and graphene at fluid-fluid interfaces

J. Samaniuk. Chemical and Biological Engineering, Colorado School of Mines, Golden, CO. Email: samaniuk@mines.edu

The ability to form films and coatings from particles at fluid-fluid interfaces via Langmuir-Blodgett, Langmuir-Schaefer, or roll-to-roll techniques is well known. When film properties depend strongly on the morphology of the deposited film, as is the case with conductive films that require the formation of a percolated particle network, then the dynamics of film formation at the fluid-fluid interface are important. Recently it was discovered that few-layer graphene is thermodynamically stable at a heptane-water interface, and that conductive, transparent films can be readily formed from such an interface. Although the dynamics of graphene sheet interaction in this system are especially important for the tradeoff between film conductivity and transparency, those dynamics are not understood. We have performed dynamic measurements in a Langmuir-Blodgett trough to improve our understanding of this system, and have utilized Brewster Angle Microscopy, microscopy from depositions on mica substrates, and long-time relaxation measurements to probe film structure and dynamics. In this presentation I will discuss the progress we have made in the last year investigating graphite and graphene particles deposited at air-water, and oil-water interfaces.

CSSS 12

Measurements & Models of kT-Scale Microcapsule-Substrate Interactions to Optimize Fragrance Delivery

M. Bevan1, I. Torres1, A. Coughlan1, H. Jerri2. 1Johns Hopkins University, Baltimore, MD, 2Firmenich, Inc., Plainsboro, NJ. Email: mabevan@jhu.edu

Designing functional capsule delivery systems that are stable against aggregation during storage, deposit on target substrates, and release contents at controlled rates is essential for drug delivery, food products, cosmetics, personal care, and home care applications. Significant engineering challenges remain for designing capsules and formulation compositions with physicochemical properties to achieve an optimal combination of stability, deposition, and release characteristics. In this work, we report the development of direct measurements to reveal fundamental mechanisms as well as a mathematical models of the observed phenomena to provide interpretive/predictive capabilities for formal engineering of capsules and formulations. Using an integrated suite of optical microscopy and image analysis tools, potential energy profiles and deposition lifetimes are obtained for various capsule chemistries and shapes on glass substrates as a function of added salt, surfactant, and polymer. Deposition behavior vs. surfactant and polymer concentrations shows non-monotonic behavior where deposition only occurs when specific binding mechanisms contribute significantly. To address how colloidal interactions are coupled to particle shape effects, the Derjaguin approximation is employed in conjunction with half-space results to model the interaction potentials of various composite particle shapes that capture essential buckled capsule features. After demonstrating how computer simulations match microscopy observations of deposition behavior, simulations were used to explore how formulation composition as well as capsule size and chemistry can be designed to optimize capsule-substrate interactions, dynamics, and deposition. Ongoing and future extensions of this work include understanding synergistic interactions between formulation components and further refinement of computer simulations for formal design, control, and optimization of fragrance delivery systems.

CSSS 13

Unjustified Assumptions: How to avoid dysfunctional Industry-Academic Collaborations

P. Spicer. The University of New South Wales Sydney, Sydney, AUSTRALIA. Email: p.spicer@unsw.edu.au

As engineering undergraduates we have a key concept drilled into us: make assumptionsbut justify them! This is an extremely effective method of simplifying, and ultimately solving, technical problems that would be intractable without such treatment. When we move into industry, or academia, this mindset can carry through to interactions with one another and actually be more limiting than enabling. Ive worked in both industry and academia, and have interacted with my counterparts while trying to solve technical problems with commercial and scientific value. A key guiding principle that emerged from successful and unsuccessful endeavours in these areas is that industrialists and academics often approach one another with flawed, or limiting, assumptions that can hinder or negate their good intentions. Ill present several exemplary case studies and talk about how we can be the most effective collaborators across disciplines and sectors, hopefully expanding your ability to approach and solve some of the best problems out there.

CSSS 14

To be determined

K. Stebe. University of Pennsylvania, Philadelphia, PA. Email: kstebe@seas.upenn.edu

To be determined

CSSS 15

Multiple emulsions: scaling up and scaling down

M. E. Helgeson. Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA. Email: helgeson@ucsb.edu

Multiple emulsions - i.e. droplets within droplets - are attractive encapsulation and delivery vehicles due to their ability to co-encapsulate compounds with widely varying solubility within their multi-phase structure. As such, they have been explored for a range of formulated fluid technologies including consumer products, foods, cosmetics, pharmaceuticals and nanobiotechnology. Recent advances in microfluidic methods to produce multiple emulsions with exquisite control have opened up a wide new design space of complex multi-phase droplets, and various colloidal particles from them. However, these capabilities have yet to meet the demands of technological translation due to problems with scalability in two important respects. First, the devices used have yet to demonstrate production throughput at levels necessary for industrial implementation. Second, the size of droplets is set by the device geometry, which has limited production to droplets that are tens or hundreds of microns in size - too large to achieve colloidal stability in many conventional formulations. Here, we review several recently developed methods to produce multiple nanoemulsions - i.e. nanodroplets within nanodroplets - that overcome these limitations in scalability. By combining conventional, scalable emulsification equipment with careful control of mechanical and thermodynamic instability - both at the oil-water interface and in the bulk - these methods are able to produce large quantities of colloidally stable multiple emulsions. Various practical strategies for controlling droplet morphology, dimensions and polydispersity will be discussed. Finally, we illustrate the capabilities and challenges associated with technological translation of multiple nanoemulsions by reviewing various applications in drug delivery.

CSSS 16

Partnering to Win: Academic/Industry Collaborations

G. Baier. Dow Chemical Company, Midland, MI. Email: baierg@dow.com

Weve all been told that collaboration is important to delivering top notch science efficiently and effectively. Undoubtedly it is.but havent we all also experienced a collaboration that was, well, less than ideal? This presentation will address Dows approach to partnering with universities and its evolution. Especially in the last ten years, Dows academic collaborations have been, and continue to be, key contributors to the vitality of our research, development, and talent pipeline. Why do we collaborate? What makes a good collaboration? What makes bad collaboration? What is unique to academic - industry collaborations? How can industry and academia work together for even better collaborations?

CSSS 17

Driving Colloids with Rotating Magnetic Fields

S. L. Biswal. Chemical & Biomolecular Engineering, Rice University, Houston, TX. Email: biswal@rice.edu

One of the most exciting areas in colloidal research is the precise control of interparticle interactions to generate new structures. The ease of tuning interactions, size, shape, and composition has made these nano- and micrometer-sized particles appealing probes for a number of fundamental studies. Recent work has focused on the use of colloidal particles that can act as models for studying the fundamental phenomena of atomic systems. The self-assembly of these colloidal atoms has led to investigations of the dynamics of chemical transformations such as nucleation or phase transitions. I will describe the application of a fast rotating magnetic field to a system of paramagnetic colloids, to study statistical thermodynamics. Additionally, studies on out of equilibrium phenomena will offer novel dynamic behavior, such as colloidal microscale swimmers. Our results promise to open up new insights into magnetically actuated 2-D materials.

CSSS 18

Inkjet printing of magnetic particles towards anisotropic magnetic properties

K. N. Al-Milaji, S. M. Harstad, R. L. Hadimani, H. Zhao. Mechanical and Nuclear Engineering, Virginia Commonwealth University, Richmond, VA. Email: almilajikn@vcu.edu

The ability in tuning magnetic properties by tailoring the shape anisotropy and magnetic easy axis of nanostructured materials is promising in fabricating functional devices. One candidate that has a great potential in designing and prototyping magnetic devices is inkjet printing. In this study, Gd5Si4 magnetic nanoparticles were formulated in terpineol oil and printed onto a photopaper substrate to form a patterned film. When no magnetic field is applied, patterns ranging from uniform deposits to clear coffee rings are obtained, depending on the droplet size. While under an external magnetic field, coffee ring formation is suppressed in all the patterns. For larger inkjet droplets, the magnetic nanoparticles are assembled into chains which exhibits anisotropic magnetic properties in the printed structures.On a porous substrate like photopaper, the particle motion and solvent removal (through infiltration and evaporation) occur simultaneously during the film formation. Solvent infiltration is much faster than evaporation and particle motion. For small droplets, the porous substrate can fully imbibe the solvent, the colloidal nanoparticles are immobilized and deposited onto the substrate due to the fast removal of the solvent. When droplet size increases, the solvent is partially imbibed into the substrate; the nanoparticles are observed to migrate to the contact line of the remaining solvent, by evaporation-induced capillary flow producing the ubiquitous coffee-ring deposition. When a magnetic field is applied, the magnetic particles move towards the substrate under the magnetophoretic force overcoming the evaporation-induced flow, no matter whether the solvent is fully or partially imbibed into the substrate. In addition, the horizontal component of the magnetic field, drives the magnetic particles forming long chains especially for the larger droplets when the solvent is partially imbibed into the substrate. The chain formation in the magnetic nanoparticle assembly enhances the anisotropic magnetic properties which provides a great potential in many engineering applications such as magnetic cooling devices and thermal energy harvesting.

CSSS 19

Tuning the dielectrophoretic assembly of particles through surface functionalization

N. D. Burrows, C. D. Keating. Department of Chemistry, Pennsylvania State University, University Park, PA. Email: nub90@psu.edu

The directed self-assembly of particles in a non-uniform electric field can be achieved due to the phenomenon of dielectrophoresis resulting in an applied force. The strength of this force depends on the polarizability of both the particles & suspending medium, the particles size and shape, and the frequency of the electric field. The Claussius-Mossotti Factor, a frequency dependent function of both the particle and medium complex dielectric constant, determines the direction and magnitude of particle response to applied AC fields and changes with charge carrier density. Surface functionalization can alter the mobility of the charges associated with the particle surface electrical double-layer and presents an opportunity to further tune the dielectrophoretic (DEP) response. Here in we present the DEP assembly of particles tuned by various surface chemistries and demonstrate the importance of surface charge mobility in DEP assembly.

CSSS 20

Enabling low voltage electrophoretic deposition of semiconductor nanocrystals

A. T. Fafarman. Chemical Engineering, Drexel University, Philadelphia, PA. Email: fafarman@drexel.edu

For electrophoretic deposition (EPD) to achieve its potential as a method for assembling functional semiconductors it is critically necessary to significantly reduce the threshold voltage for deposition. Herein we demonstrate that post-synthetic modification of the surface chemistry of all-inorganic colloidal copper-zinc-tin-sulfide (CZTS) nanocrystals (NCs) enables EPD at voltages as low as 4Va three-fold or greater improvement over previous examples of non-oxide semiconductors. The chemical exchange of the original surfactant-based NC-surface ligands with selenide ions yields essentially bare, highly surface-charged NCs. Thus, both the electrophoretic mobility and electrochemical reactivity of these particles are increased, favoring deposition. In situ imaging of the reactor during deposition provides a quantitative measure of the electric field in the bulk of the reactor; this, coupled with chronoamperometry, reveals the fundamental reaction and mass transport limitations of low-voltage EPD. A crossover from mass transport-limited to reaction rate-limited EPD is observed. Under the later conditions, the influence of gravity can result in boundary-layer instabilities that are severely deleterious to the uniformity of the deposited film. This knowledge is applied to deposit thick, uniform and crack-free films without sintering from stable, well-dispersed colloidal starting materials.

CSSS 21

High-throughput assembly of colloidal crystals by acoustophoresis

M. Akella, J. Juarez. Mechanical Engineering, Iowa State University, Ames, IA. Email: makella@iastate.edu

Colloidal crystals are encountered in a variety of energy-harvesting applications, where they serve as waveguides or filters for electromagnetic and electro-optic energy. Techniques such as electric or magnetic assembly are used to assemble colloidal crystals, but are limited by crystal size, yield, and throughput. This article demonstrates the continuous, high-throughput assembly of two-dimensional (2D)-colloidal crystals in an acoustofluidic flow cell. The device is fabricated using off-the-shelf components and does not require a clean-room access. An experimental state diagram shows how the fluid flow rate and voltage applied to the piezoelectric element in our device can tune the crystal microstructure. Highly ordered colloidal crystals are continuously assembled in less than a minute with a throughput yield of several hundred particles per minute using this device. The acoustically assembled ordered 2D crystals are immobilized using a UV-curable resin and extracted as ordered polymer-particle fibers, demonstrating the ability of using acoustic fields to assemble ordered structures embedded in bulk materials. Particle tracking is used to construct the cross-channel particle distribution to understand the effect of acoustic compression on colloidal crystal assembly. Microparticle image velocimetry data is compared to a theoretical transport model to quantify the effect fluid flow and acoustic trapping has on the colloidal crystal ensemble.

CSSS 22

Multi-compartment Cerberus nanoemulsions created by flow-induced droplet fusion and by self-limiting coalescence

T. G. Mason. Chemistry & Physics, UCLA, Los Angeles, CA. Email: mason@chem.ucla.edu

We have fabricated multi-compartment nanoscale droplets containing three different types of immiscible oils in an aqueous surfactant solution using two different methods of fusion processing. In the first method, we take advantage of flow-induced coalescence that also accompanies flow-induced rupturing in high flow-rate emulsification (HFRE) driven by a microfluidic homogenizer. We make three different microscale oil-in-water (O/W) emulsions, each containing simple single droplets and made using a different type of oil (e.g. aliphatic, aromatic, or fluorinated silicone oil). We combine these three emulsions initially at low flow rates without inducing any droplet coalescence and then process this complex microscale emulsion using HFRE to cause both droplet rupturing and coalescence. Because these three types of silicone oils are all mutually immisible as well as immiscible with water, the flow-induced fusion process leads to internal oil-oil interfaces within the resulting nanodroplets. Simultaneously, however, droplets are also broken down, indicating that HFRE causes both interfacial coalescence and droplet rupturing instabilities. Using cryogenic transmission electron microscopy (C-TEM), we show that a dominant compartmentalized nanodroplet morphology emerges as a consequence of repeated rupturing and coalescence events. In keeping with the latin designation of Janus for two-compartment droplets, we call such three-compartment droplets "Cerberus droplets", referring to the mythical 3-headed dog guarding the realm of Hades. Moreover, we comment on the effects that 2-liquid surface tensions and 3-liquid line tensions can have on the formation and stability of these multi-compartment nanodroplets. As a second different method, we take advantage of self-limiting fusion reactions of droplets mediated by molecules that temporarily reduce the stability of droplets against coalescence. As an example, we mix an O/W emulsion containing two or three different immiscible oil types, stabilized by an anionic surfactant, sodium dodecyl sulfate (SDS), with a solution of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Depending on the molarities of surfactant in both the anionic O/W emulsion and the cationic solution, we find that a regime exists in which only limited droplet coalescence occurs before restabilization of the droplet interfaces globally in this mixture. If the starting oil droplets are nanoscale and three different immiscible oil types are used, then this second approach can also be used to create Cerberus nanodroplets that have different morphologies compared to the first approach, as we reveal using C-TEM. We have also shown that similar self-limiting coalescence reactions can be made between an SDS-stabilized O/W emulsion and a CTAB-stabilized O/W emulsion containing a different immiscible oil. In addition, we have demonstrated that this self-limiting fusion approach can be used over a wide range of droplet sizes, from the microscale to the nanoscale. Since drug molecules can have different solubilities in different oil types, these multi-compartment nanodroplets can be loaded with different drugs in different compartments, suitable for localized drug co-delivery applications.

CSSS 23

Dynamics of partial coalescence and destabilization in 2D monodisperse emulsions

S. Abedi, C. Chen, S. Vanapalli. Texas Tech University, Lubbock, TX. Email: samira.abedi@ttu.edu

Dynamics of partial coalescence and destabilization in 2D monodisperse emulsionsSamira Abedi, Chau-Chyun Chen and Siva A. Vanapalli Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409-3121, USAEmulsions with partially crystalline droplets are functional materials that may undergo destabilization due to coalescence of droplets during phase transition. This destabilization process has a dramatic impact on emulsion thermal and flow properties, yet the determining factors and underlying mechanism of emulsion destabilization due to partial coalescence are poorly understood. Here, we use microfluidics to generate monodisperse n-hexadecane-in-water emulsions to visualize the in situ partial coalescence and subsequent destabilization in an initially 2D array of droplets. We monitor multi-body coalescence events occurring in the 2D emulsion during the thermal cycling and determine the final droplet size distribution. We observe that destabilization proceeds initially through the formation of 2-5 droplet clusters followed by coalescence of these clusters to form large-scale nonspherical aggregated structures. By investigating the influence of initial droplet size in the array, we find that smaller droplets undergo less destabilization since the formation of large-scale nonspherical structures is inhibited. This propagation of coalescence observed in the partially crystalline emulsions has features similar to that reported in 2D emulsions where the droplets are not crystalline [1]. Additional results on the influence of physicochemical factors affecting the destabilization process will be reported.[1] N. Bremond, H. Domjean, and J. Bibette, "Propagation of drop coalescence in a two-dimensional emulsion: A route towards phase inversion," Physical review letters, vol. 106, no. 21, p. 214502, 2011.

CSSS 24

Microfluidic production of phase separated cellular mimics

C. D. Crowe, C. D. Keating. Chemistry, Pennsylvania State University, University Park, PA. Email: cdc217@psu.edu

The living cell provides a complicated, non-ideal environment for housing biological reactions. Modeling this in artificial cells requires replicating aspects of the cellular environment not typically found in biochemical studies. Phase separated solutions fulfill this need by providing both macromolecular crowding and membraneless compartmentalization, physical aspects found in living systems. Utilizing solutions of neutral polymers or charged polyelectrolytes, cellular mimics may be produced that contain distinct, chemically unique regions. These provide preferential partitioning of biological reagents and differing solution environments within a contained aqueous system. In this research, artificial cells were formed as multiphase water-in-oil emulsion droplets, allowing simultaneous observation of multiple, separated experimental systems. Additionally, microfluidics provides a path to exercise control over the aspects of these droplets, producing monodisperse solutions of multiphase droplets with varying internal characteristics. Droplets were formed containing aqueous two-phase systems of polyethylene glycol (PEG) and dextran with varying concentrations. The total size of the droplets and relative phase volumes of each phase within the droplets were controllable via microfluidics. Additionally, coacervate-containing droplets were produced from several different polyelectrolyte compositions. The formation and dissolution of the coacervates within the droplets was controlled after droplet production via heating and cooling the emulsion solution. The production of these cellular mimics provides a method by which unique physical and chemical aspects of the cell may be modeled, explored, and varied.

CSSS 25

Complex multi-compartment and internally ordered emulsions

X. Wang1, Y. Zhou2, Y. Kim1, M. A. Tsuei1, K. Iwabata1, J. J. de Pablo2,3, N. L. Abbott1. 1Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI, 2Institute for Molecular Engineering, University of Chicago, Chicago, IL, 3Argonne National Laboratory, Chicago, IL. Email: xwang867@wisc.edu

Oil in water emulsions are encountered in a wide range of contexts, including within foods, in pharmaceutical preparations and as templates for materials synthesis. More recently, emulsion droplets with increasingly complex internal organizations have been explored, including multi-compartment emulsion droplets and emulsion droplets comprised of structured oils such as liquid crystals (LCs). The latter, in particular, offer the basis of systems that undergo changes in organization and optical properties in response to subtle stimuli such as bacterial lipids. This presentation will report an investigation of multi-compartment emulsions where one compartment is a liquid crystalline oil. The work is motivated by the long-range goal of designing complex emulsion droplets that can reorganize to generate optical responses to a range of triggers, including the presence of amphiphiles. Because confinement of LC domains within non-spherical compartments of multicompartment emulsion droplets changes the surface-energetic and elastic contributions to the free energy, we hypothesized that multicompartment LC-containing emulsions may offer the basis of LC systems with optical properties and responsiveness not found in spherical systems. We tested this hypothesis by characterizing the morphologies and internal organization of Janus droplets with nematic compartments using hydrogenated and fluorinated compounds, namely E7 and perfluorobenzene. A particularly interesting set of observations demonstrate that the morphologies of the Janus droplets dispersed in aqueous solutions can be controlled by taking advantage of the selective interaction of hydrocarbon or fluorocarbon surfactants with hydrocarbon and fluorocarbon-rich domains of the droplets. Additional insights regarding the surface anchoring and internal ordering of the LC within the Janus emulsion droplets are obtained by using numerical simulations. Overall, these results hint at principles for the design of complex and internal ordered emulsions with reconfigurable compartments and may lead to new ways of designing materials capable of responding to molecular signals with macroscopic responses.

CSSS 26

Directional Emission from Dynamic Complex Emulsions

L. Zeininger, T. M. Swager. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA. Email: lukaszei@mit.edu

Rapid Detection of Foodborne Pathogens using Directional Emission from Dynamic Complex EmulsionsLukas Zeininger and Timothy M. SwagerMultiphase complex emulsions formed from two or more immiscible solvents offer a unique platform as new materials for chemical sensor applications. The temperature controlled miscibility of fluorocarbons (F) and hydrocarbons (H) enables a temperature induced phase-separation, leading to structured emulsion droplets of H and F in water (W), which can be alternated between encapsulated (F in H, and H in F), and Janus configurations by varying the interfacial tensions using surfactants. These complex emulsion droplets can selectively invert morphology in response to external stimuli such as the presence of specific analytes, small pH changes, light or high energy irradiation, and the presence of an electric or magnetic field. This, in combination with the unique optical properties of our emulsion droplets enables the application of our complex emulsions as a new transduction material for chemo- and bio-sensing applications. Here, we will show how the addition of stimuli-responsive surfactants to the complex emulsions provides a method to induce a morphology change or droplet reconfiguration as a response to the presence of specific chemical or biological analytes. In order to create a ratiometric optical read-out of small changes in the droplet morphology, emissive dyes were added to one of the two immiscible phases of the complex emulsions. The potential of these micro-colloids to manipulate light in form of waveguides led to the development of several optical transduction methods, where an adjustment of the refractive indices of the solvents results in a new unprecedented control of light propagation inside the emulsion droplets. We will demonstrate that having control over the total internal reflection of light from outside and inside the emulsion droplets results in new sensory schemes for the rapid and sensitive detection of various chemical and biological analytes, including common foodborne pathogens such as Salmonella and E.coli bacteria.

CSSS 27

Engineering New Membranes for Critical Environmental Challenges

L. Li1, W. Zhong1, C. Ji1, J. Hou1,2, V. Chen1. 1Chemical Engineering, University of New South Wales, Sydney, AUSTRALIA, 2Materials Science & Metallurgy, Cambridge University, Cambridge, UNITED KINGDOM. Email: v.chen@unsw.edu.au

Growing environmental applications in water and wastewater treatment, more recalcitrant streams such as hypersaline feeds, highly fouling biological effluents, and micropollutants pose growing challenges as the demands for water reuse and resource recovery increase. These require both new functionality of membrane materials as well as new processes such as membrane distillation and pervaporation for separation, biocatalytic reactors, and enzymatic fuel cells.We have synthesized new nanocomposite polymer membranes with inorganic coatings as well as blending of 1D, 2D and 3D (framework) materials to enhance membrane performance. Recently, we have developed techniques using inorganic sol-gel and biomineralization approaches to coat polymeric membranes to form low fouling, superhydrophobic/hydrophilic (Janus) interfaces, and substrates for enzyme immobilization for micropollutant degradation. Incorporation of defect engineered metal organic framework materials has been applied to enhance performance of dense film coatings of membrane distillation /pervaporation membranes for the dewatering of hypersaline effluents utilizing low value heat. Scaleable coating of 2D materials for desalination and water treatment poses also new opportunities beyond conventional polymeric materials. Deposition of grapheme oxide onto porous membranes offer high efficiency removal of low molecular weight contaminants as well as very high salt rejection from concentrated brines.

CSSS 28

Water desalination by capacitive deionization methods

K. Tang1, J. Gabitto2, S. Yiacoumi1, C. Tsouris3. 1Georgia Institute of Technology, Atlanta, GA, 2Prairie View A&M University, Praire View, TX, 3Oak Ridge National Laboratory, Oak Ridge, TN. Email: tsourisc@ornl.gov

Water desalination by capacitive deionization methodsKexin Tang,1 Jorge Gabitto,2 Sotira Yiacoumi,1 Costas Tsouris1,31School of Civil and Environmental Engineering, Georgia Institute of Technology2Department of Chemical Engineering, Prairie View A&M University3Enegy and Transportation Science Division, Oak Ridge National LaboratoryCapacitive deionization (CDI) is a desalination technology employing less than 1.6-V potential to remove ions from saline solutions. CDI can be more energy efficient than pressure- or heat-driven desalination processes, including reverse osmosis and multistage flash distillation. Because of coion repulsion during charging and re-adsorption during discharging, however, the performance of CDI is yet to meet practical requirements. Membrane CDI (MCDI) addresses these issues by limiting coion transfer through cation and anion exchange membranes. Efforts have been made to achieve high electrosorption capacity and fast kinetics using MCDI through electrode materials development, new cell design, and process optimization. The MCDI performance, however, is still limited. Two methods are proposed here to enhance electrosorption: over-potential MCDI with reversed polarity (OP-MCDI-RP) and flow-electrodes CDI (FCDI). Seawater desalination experiments have shown that the OP-MCDI-RP system reduced the electrical conductivity of natural seawater of 37 practical salinity units by 99.9%, suggesting that this system can be employed for seawater desalination. FCDI provides high surface area for ion capture through self-regeneration of flowable electrodes (FEs) and by discarding polymer binders. A fundamental issue for FCDI is the low electrical conductivity of FEs, due to the high intrinsic resistance of aqueous electrolytes. Here, the electrolyte concentration and carbon materials are optimized by testing several carbon powders. Results indicate that FEs can demonstrate high salt storage capacity. The OP-MCDI-RP and FCDI systems are expected to lead to commercial applications for the desalination of widely ranging salinity water. Theoretical description of electrosorption is introduced for both methods.

CSSS 29

Moringa oleifera f-Sand Filters for SustainableWater Purification

b. xiong1, B. Piechowicz1, Z. Wang1, R. Marinaro2, E. Clement1, A. Uliana1, M. Kumar1, S. Velegol1. 1Pennsylvania State University, Pennsylvania State University, University Park, PA, 2School of Chemical, Biological, and Materials Engineering, University of Oklahoma, University Park, OK. Email: boya.xiong@gmail.com

The purpose of this article is to determine parameters for the design of a Moringa seed sand filter for water purification. Moringa oleifera seeds containing cationic antimicrobial proteins have been used as natural coagulants for turbidity removal; however, the low removal efficiency and high residual organic levels limit their applications. In this work Moringa seed extracts were used to reverse the charge of sand (f-sand) to +10 mV at a seed dosage of 5.6 g seed/m2 sand. This f-sand filter demonstrated around 4 log removal of 1 m polystyrene particles and more than 8 log removal of E. coli. compared to less than 0.1 log removal for bare sand. Enhanced removal for particles and E. coli was dominated by attractive electrostatic interactions. Clean bed filtration modeling predicts a sticking coefficient (alpha) of 0.8 for f-sand compared to 0.01 for bare sand. This alpha was further validated under a wide range of filtration conditions. Preliminary scale-up analyses suggest a point-of-use f-sand filter that requires very low amount of seeds annually. The outcome of this work presents the scientific basis for the design of a water purification solution for developing regions, requiring only locally available resources and no use of synthetic chemicals or electricity.

CSSS 30

Measurement of nanoparticle sticking coefficients for Moringa-coated sand filters

L. Samineni1, B. Xiong2, S. Velegol1, M. Kumar1, D. Velegol1. 1Department of Chemical Engineering, The Pennsylvania State University, State College, PA, 2Department of Civil and Environmental Engineering, The Pennsylvania State University, State College, PA. Email: lxs480@psu.edu

The objective of the work presented in this talk is to measure the sticking coefficient (alpha) of viruses and nanoparticles independently of a packed column filter. The growing need for sustainable, cost-effective water treatment solutions have led to a search for alternate methods based on plant materials like Moringa oleifera seeds. Research efforts in our group have demonstrated that the surface of sand particles can be functionalized (f-sand) using antimicrobial cationic protein present in Moringa seed extract. Column filters packed with f-sand showed 99.999999% removal (8-Log) of E. coli in PBS buffer (0.016M) compared to less than 90% removal (1-Log) achieved by columns packed with uncoated sand. To form a basis for design and scale-up, removal efficiencies from experiments with model particles (1 micron polystyrene spheres) were interpreted using classic clean bed filtration (CBF) models. CBF models accurately predict the removal of micron-sized particles with alpha approximately equal to 1, but literature suggests that CBF models over-predict the removal of nanoparticles when alpha is 1. We hypothesize that the alpha for nanoparticles is much lower than that for micron-sized particles due to lower surface interactions. To test this hypothesis, we designed an experimental technique based on microscopy to measure alpha independently of a packed column. In this talk, we describe the technique and results obtained from these experiments, which appear to explain the over-prediction of nanoparticle removal by CBF models. Our method for measuring alpha can be used more broadly, so that CBF models give more accurate predictions of removal for particular virus and nanoparticle systems.

CSSS 31

Stability and transport of two different TiO2 nanoparticles in the Canadian environment

J. Farner Budarz1, J. De Tommaso2, R. Cheong1, H. Mantel1, N. Tufenkji1. 1Chemical Engineering, McGill University, Montreal, QC, CANADA, 2Chemical Engineering, Politecnico di Torino, Turin, ITALY. Email: jeffrey.farner@mcgill.ca

TiO2 nanoparticles (NPs) are increasingly being incorporated into paints and self-cleaning surface coatings due to their light absorption and photocatalytic properties. Given that NPs are regulated as new substances, there is the need to develop and improve our understanding of NP fate and transport in groundwater systems. Studies of a materials transport and deposition in saturated granular porous media have been largely limited to a single source of NP, assuming its behavior to be representative. Here, we investigate two commercially available TiO2 NPs that differ both in particle size and mineral form: P25 (Degussa, Germany) is a commonly studied preparation of 25 nm particles of anatase and rutile forms in roughly an 80/20 ratio, while CoRI C (Coatings Research Institute, Belgium) is a nanoparticulate paint additive composed of 100% anatase at 5-10 nm. One particular gap in our understanding of NP stability occurs at low temperatures, where suspended NPs may be subjected to a freeze / thaw cycle, which often occur at seasonal interfaces.The objectives of this work were to study the mobility of two different TiO2 NPs in model aqueous environments at 10 C to investigate the differences in commercial and commonly researched reference NPs. Both pristine and natural organic matter (NOM) coated NPs were employed. Furthermore, NPs were subjected to a freeze / thaw cycle to observe the impact of freezing on NP aggregation and deposition. Results indicate that while trends are consistent, the two types of NPs studied here exhibit different degrees of mobility in a column packed with quartz sand. For both NPs, transport is reduced as ionic strength increases from 1 100 mM, although the addition of up to 10 ppm NOM increases stability. The attachment efficiency of P25 was more influenced by the presence of NOM than CoRI C. Freezing suspensions of TiO2 NPs led to increased aggregation and reduced transport compared to samples run under the same water chemistries but not exposed to the freeze / thaw cycle. These results suggest that predictions of NP transport should take into account not only the NP material but also the morphology of the particles. Furthermore, variations in temperature and exposure to freezing conditions are likely to have a large impact on NP transport in the environment.

CSSS 32

Developing potential designer rules for aptamer libraries

V. Milam1, R. Sullivan, 303321, M. Adams1, R. Naik2. 1Georgia Institute of Technology, Georgia Institute of Technology, Atlanta, GA, 2Georgia Institute of Technology, ARFL, WPAFB, OH. Email: valeria.milam@mse.gatech.edu

Single-stranded oligonucleotide ligands called aptamers bind to non-nucleotide targets with a specificity and affinity that rival that of antibodies. Numerous DNA aptamers have been identified for biological targets such as soluble proteins; however nonbiological materials such as colloidal particles, however, have received far less attention as a potential target species for aptamer screening and implementation. Furthermore, aptamers are conventionally identified using an evolutionary screening process called "Systematic Evolution of Ligands by Exponential Enrichment" (SELEX) in which a pool of approximately 1016 random candidate sequences is continuously enriched with amplified copies of winning sequences or adsorbates from prior selection rounds.. Here, we employed a non-SELEX screening approach we call CompELS (Competition-Enhanced Ligand Selection) to quickly, yet reliably identify candidate aptamers against colloidal gold targets. Though no clear sequence segment patterns emerged among the CompELS-identified aptamer candidates, common secondary structural motifs and global patterns were identified among seemingly unrelated aptamer sequences using a combination of UNAFOLD and a modified version of CLUSTAL software analysis. By identifying secondary structure elements that may serve as target binding motifs, we aim to eventually replace purely random sequence libraries with more informed screening libraries possessing promising binding motifs.

CSSS 33

Combined Effects of Temperature and Compression/Dilation of an Air-Water Interface on Therapeutic Protein Aggregation

C. V. Wood1, V. I. Razinkov2, W. Qi2, E. M. Furst1, C. J. Roberts1. 1Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, 2Drug Product Development, Amgen, Thousand Oaks, CA. Email: caitlinw@udel.edu

Therapeutic monoclonal antibodies (mAbs) are the largest overall selling class of biologics and consist of many approved and prospective therapies that are in clinical trials. As proteins, one obstacle to mAb development is their propensity to degrade and aggregate. Protein aggregation can occur by a number of pathways that can depend on the identity of the protein as well as the solution environment and the nature of the stress. In bulk solution, monomer self-assembly has been extensively investigated and is hypothesized to occur through transient and relatively weak interactions that can be affected by changing solution pH, ionic strength, or ion type to alter electrostatic interactions between monomers. Aggregates can also form through a less-understood process that is initiated when proteins adsorb to bulk interfaces. Aggregation at interfaces results in protein films that putatively desorb into solution as particles when the interfaces are agitated and/or destroyed.This work evaluates the combined effects of temperature and compression/dilation of air-water interfaces on aggregation rates and particle formation for representative mAb formulation conditions for a model mAb. High-pressure liquid chromatography is used to monitor monomer loss over time, which is converted to a rate constant that can be fit to an Arrhenius rate equation. Turbidity and particle counting techniques are used to monitor conversion of protein to macroscopic and subvisible particles. Comparison of results from quiescent and agitated conditions indicates that surface-mediated aggregation continues to be important even at elevated temperatures. Aggregation rates and the size and structure of particulates can vary depending on the temperature and pH of the solution. The results will be presented and discussed in terms of applications in elucidating mechanisms of surface-mediated protein aggregation.

CSSS 34

Controlled Delivery of Signaling Molecules using Magnetic Microrobots

S. Das1, E. E. Hunter2, E. B. Steager2, V. Kumar2. 1Chemical and Biomolecular Engineering, University of Pennsylvania, philadelphia, PA, 2GRASP Laboratory, University of Pennsylvania, philadelphia, PA. Email: sambeeta@seas.upenn.edu

Magnetically-actuated microrobots have many potential applications in biological environments. These microrobots have found many uses in cellular environments since they can be remotely actuated and precisely manipulated in biochemical fluids. Most cellular phenomenon depend on biochemical signals. Therefore various techniques have been developed for encapsulation and release of drugs, nutrients or other cargo using microrobots. In this work, we present a light-controlled delivery system complexed with magnetic microrobots. We synthesize a photolabile linker which releases a cell-to-cell signaling molecule when exposed to light. This system is integrated with magnetic microrobots which can be steered to target locations in the cell culture. We demonstrate that the gene expression in engineered E. coli cells is successfully activated when the signaling molecule is cleaved. This proposed method can be used for wide ranging applications in the fields of engineering, biology and medicine, in applications where the ability to target and release molecules on demand to a particular location is very important.

CSSS 35

Investigating dehydration-induced physical strains of cellulose microfibrils in plant cell walls

S. Huang1, M. Makarem1, S. N. Kiemle2, Y. Zheng2, X. He1, D. Ye1, E. W. Gomez1, E. D. Gomez1, D. J. Cosgrove2, S. H. Kim1. 1Chemical Engineering, The Pennsylvania State University, University Park, PA, 2Biology, The Pennsylvania State University, University Park, PA. Email: szh200@psu.edu

The sum frequency generation (SFG) spectral features of cellulose are known to be sensitive to the nano-scale crystalline packing of cellulose chains and the meso-scale structural order of cellulose microfibrils in plant cell walls and biomass. This technique, along with microscopic imaging, was used to study the effect of dehydration on the physical status of cellulose microfibrils (CMFs) in primary cell walls (PCWs) using onion epidermal walls as a model system. The SFG spectra of cellulose in the dehydrated onion epidermal wall have broad peaks centered at ~2915 cm-1 and ~2964 cm-1 in the alkyl stretch region, while those in the never-dried or rehydrated walls have a relatively sharp peak at 2944 cm-1. Since no chemical change occurs upon simple air-drying of onion epidermal walls, the changes in the SFG spectral features must be associated with the collapse of the hydrated soft matrix networks of pectin in the intact cell wall into a glassy hard matrix in the dried cell wall. A similar behavior was observed even in the fully-hydrated state when the pectin network was cross-linked by exogenously added Ca2+ ions. These results suggested that the physical collapse of the pectin matrix, in which CMFs are interspersed, could induce local strain or distortion of CMFs. Although the modulus of cellulose crystals is known to be high, the force needed to bend CMFs is very small because the diameter of CMFs in PCWs is only ~3.5 nm. Analysis of x-ray diffraction (XRD) data of CMFs in dried PCWs reveals that the (200) spacing between cellulose chains in crystalline domains is larger than the crystallographic spacing of cellulose I obtained from tunicates. The poor packing of cellulose chains in the (200) crystallographic axis in dried PCWs may suggest that the modulus of CMFs would be lower than those of highly-crystalline cellulose I, thus inhomogeneous local bending or strain of CMFs in dried PCWs is likely during the collapse of pectin matrix.

CSSS 36

An ultra melt resistant hydrogel from food grade carbohydrates

B. Thompson1, T. Horozov2, S. D. Stoyanov3, V. N. Paunov2. 1Chemical and Biomolecular Engineering, University of Maryland, College Park, College Park, MD, 2School of of Mathematics and Physical Sciences (Chemistry), University of Hull, Hull, UNITED KINGDOM, 3Unilever R&D Vlaardingen, Vlaardingen, NETHERLANDS. Email: benthompson7791@gmail.com

We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agarMC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agarMC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agarMC hydrogel has enhanced mechanical properties over the temperature range 2585 C and a maximum storage modulus at 55 C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a solgel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agarMC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agarMC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 C its structure was retained without melting. The produced highly thermally stable hydrogel can be used in high temperature food structuring and an example is given where a slurry of hydrogel beads of this composition reduces caloric density of a bakery product by controlled amounts up to 25%.

CSSS 37

Optimization of Liposome-Hollow gold nanoparticle for mRNA delivery

A. Veeren1, M. J. Osborn2, S. Merkel3, J. Shin1, J. A. Zasadzinski1. 1Department of Chemical engineering and Material science, University of Minnesota, Minneapolis, MN, 2Department of Pediatrics, University of Minnesota, Minneapolis, MN, 3Stem Cell Institute, University of Minnesota, Minneapolis, MN. Email: aveeren@umn.edu

mRNA therapy has gathered great interest because of its potential role for the transient modification of immune cells for treatment of an array of diseases. However, the main obstacle preventing routine mRNA immune cell transfection is the lack of a high viability, high efficiency, high throughput delivery system. Due to its sensitivity towards catalytic hydrolysis, unprotected mRNA cannot be delivered by itself. We propose encapsulating mRNA in neutral liposomes decorated with cell internalizing peptides and hollow gold nanoshells (HGN). We use passive entrapment of lightly condensed mRNA in phospholipid-cholesterol bilayer liposomes incorporating polyethylene-glycol-lipid tethered TAT and HGN. Following TAT induced endocytosis, we can irradiate the cells with picosecond pulsed near infra-red light to induce vapor nanobubbles around the HGN that can rupture both the liposomes and the endosomes, thereby releasing the MRNA to the cell cytoplasm, where the mRNA can produce the proteins of interest. We will present our work toward the realization of this light triggered mRNA delivery system.

CSSS 38

Fundamental aspects and applications of star polymer adsorption at fluid interfaces

R. D. Tilton. Department of Chemical Engineering and Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA. Email: tilton@cmu.edu

Purpose: Nanoscale polymer brushes, including polymer-grafted nanoparticles, molecular bottlebrushes and star polymers, display interfacial characteristics that make them an interesting new class of surfactants for fluid or solid/liquid interfacial engineering applications. This presentation emphasizes fluid interfaces, where star polymers are noteworthy for their performance as highly efficient emulsifiers and foaming agents. It is well-established that emulsification and emulsion stabilization against coalescence and/or Ostwald ripening are sensitive to interfacial dilatational elasticity. Motivated by high efficiency emulsification and foaming, the purpose of this work is to determine how star polymer architecture and composition govern their adsorption from solution and resulting interfacial tension isotherms and dilatational moduli under both low amplitude and high amplitude deformations. Ultimately, correlations are sought that may be predictive for increasingly efficient emulsification or foaming.Materials and Methods: A variety of star polymers are synthesized by atom transfer radical polymerization. These include multi-arm poly(ethylene oxide) star polymers with a cross-linked core and star polymers with either 14 or 21 arms grafted from a functionalized beta-cyclodextrin core. Cyclodextrin-core star polymers that have homopolymer or diblock copolymer arms are under investigation. The arms consist of nonionic poly(diethylene glycol)methyl ether methacrylate (PMEO2MA) or the weak polycation poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) or block copolymers of the same. These are adsorbed from solution at air/water, cyclohexane/water or xylene/water interfaces. For the two oil/water interfaces, cyclohexane is a poor solvent and xylene is a good solvent for each polymer composition. Electrostatic effects are manipulated via the pH-dependent degree of ionization of PDMAEMA and by control of aqueous phase ionic strength. Interfacial tension isotherms are measured by pendant drop tensiometry. This is also used to measure dynamic dilatational moduli in low amplitude oscillatory dilatation measurements and quasi-static dilatational moduli during large amplitude interfacial compression.Results: Star polymer adsorption produces significant interfacial tension reduction from dilute solutions, but these interfacial pressure isotherms alone are not able to distinguish efficient emulsifiers (or foaming agents) from less efficient or even ineffective ones. Dynamic dilatational moduli determined from small amplitude oscillatory dilatation experiments show little dependence on frequency in the 0.05 to 1 Hz range and are primarily elastic in character. For most star polymers considered, these dynamic moduli are very similar to the quasi-static moduli determined from large amplitude monolayer compression experiments. Different star polymers, or the same star polymers under varying pH or ionic strength conditions, or the same star polymers initially dissolved in xylene or in water, are distinguished by the dependence of their dilatational modulus on the adsorbed monolayer interfacial pressure. This dependence is loosely referred to as a dilatational signature, and work is ongoing to test its usefulness to distinguish high efficiency from low efficiency emulsifiers or foaming agents. In some special cases, spontaneous emulsification is observed depending on the phase in which the star polymer is initially dispersed, and one of the star polymers is suspected to produce thermodynamically stable microemulsions. In the latter system, emulsions form spontaneously under quiescent conditions, and a highly stable emulsion produced by high shear homogenization eventually breaks into what may either be a true microemulsion or perhaps a kinetically stable nanoemulsion, without passing through a phase inversion condition. Work is ongoing to distinguish between these possibilities.Conclusions: Star polymer adsorption, interfacial tension reduction and dilatational moduli are controlled by the solvent quality of the non-aqueous phase for the star polymer arms as well as the aqueous phase pH and ionic strength in the case of polycationic star polymers. Star polymers may be differentiated by the dependence of their dilatational moduli on interfacial pressure, a characteristic that may distinguish high form low efficiency emulsifiers and foaming agents.

CSSS 39

Tears of Wine

P. Rathore, C. Xu, V. Sharma. Chemical Engineering, University of Illinois at Chicago, Chicago, IL. Email: pratho3@uic.edu

Tears of wine refer to the rows of wine-drops that spontaneously emerge within a glass of strong wine. Evaporation-driven Marangoni flows near the meniscus of water-alcohol mixtures drive liquid upward forming a thin liquid film, and a rim forms near the moving contact line. Eventually the rim undergoes an instability, thus forming drops, that roll back into the bulk reservoir as the so-called tears of wine. Most studies in literature argue the evaporation of more volatile, lower surface tension component (alcohol) results in a concentration-dependent surface tension gradient that drives the climbing flow within the thin film. Though it is well-known that evaporative cooling can create temperature gradients that could provide additional contribution to the climbing flows, the role of thermocapillary flows is less well-understood. Furthermore, the patterns, flows and instabilities that occur near the rim, and determine the size and periodicity of tears, are not well-studied. Using experiments and theory, we visualize and analyze the formation and growth of tears of wine. The sliding drops, released from the rim towards the bulk reservoir, show oscillations and a cascade of fascinating flows that are analyzed for the first time.

CSSS 40

Adsorption dynamics and equilibrium of PEO-PDMS block copolymers at oil/water interfaces

M. L. Davidson1, M. Gottlieb2, L. M. Walker1. 1Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, 2Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheeva, ISRAEL. Email: mdavids1@andrew.cmu.edu

Adsorption of block copolymer surfactants to air/water interfaces has been studied in detail for several decades, but little data exist on their adsorption to oil/water interfaces. We have characterized the dynamic and equilibrium adsorption behavior of several oil-soluble polyethylene oxide-b-polydimethylsiloxane surfactants to oil/water interfaces using a microtensiometer platform. This platform allows the accurate determination of the initial stages of adsorption with minimal convection, allowing for precise determination of the adsorption mechanism for given solution conditions. These surfactants are quite surface activesurface activity has been seen for solution concentrations as low as 10-8 mol/L. Adsorption dynamics are strongly influenced by the curvature of the interface (a tunable parameter of the microtensiometer platform), allowing us to vary adsorption timescales over a wide range. The influence of surfactant architecture (block size, block ratio) and solution properties (concentration, solvent viscosity) on adsorption dynamics and equilibrium will be discussed. Studies of surfactant desorption will provide insight in designing appropriate experiments for studying the interfacial mechanics of these interfaces.

CSSS 41

Competitive adsorption of mAbs and excipients at the air-water interface

A. Kanthe1, M. Krause2, S. Zheng2, B. Lin3, W. Bu3, J. Strzalka4, C. Maldarelli5, R. Tu1. 1Chemical Engineering, City University of New York, City College, New York, NY, 2Drug Product Science and Technology, Bristol-Myers Squibb, New Brunswick, NJ, 3Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL, 4Time-Resolved Research, X-Ray Science Division, Argonne National Laboratory, Chicago, IL, 5Levich Institute, City College of New York, City College, New York, NY. Email: kantheankit@gmail.com

The adsorption of biomacromolecules at the air-water interface is of crucial concern in the development of new processes for antibody-based pharmaceuticals. Air-water interfaces are generated during the production, processing and storage of therapeutic formulations by pressure driven shear stress or shaking.1-3 When an air-water interface is created, the antibodies will expose their hydrophobic residues to the gas phase leading to partial unfolding, interfacial aggregation, irreversible adsorption and recruitment of additional proteins from the solution phase.4 This leads to decreased yields in production as well as a shortened shelf life of the macromolecular therapeutic drugs. Furthermore, the adsorption phenomenon will result in the conformational degradation of the antibody, where the loss of secondary and tertiary structure can result in diminished activity and promote immunogenicity, inhibiting the efficacy of the biologic drugs.5 In order to solve this problem and enhance the physical stability of therapeutic monoclonal antibodies (mAb), the pharmaceutical industry uses a multicomponent formulation that includes surface active excipients.6 Excipients are thermodynamically favored over proteins for adsorption at the air-water interface.The first part of the talk focuses on understanding the nature of single component system. The reversible/irreversible adsorption for PS-80 and mAb (mAb-1 and mAb-2) in histidine buffer is monitored. Pendant bubble tensiometer is used to characterize the equilibrium and dynamic surface tension. Additionally, a double-capillary setup of the pendant drop tensiometer is used to exchange mAb solutions with histidine buffer. The second part focuses on the competitive adsorption of the mAb and excipient system using X-ray reflectivity. A box-refinement method based on the model independent approach is used to predict the structural information on an Angstrom scale. The surface activity of the mAbs is correlated to the hydrophobic patches present on the protein surface using a parameter termed Spatial Aggregation Propensity (SAP).71. Nidhi, K., Indrajeet, S., Khushboo, M., Gauri, K. & Sen, D. J. Hydrotropy: A promising tool for solubility enhancement: A review. Int. J. Drug Dev. Res. 3, 26-33 (2011).2. Maa, Y. F. & Hsu, C. C. Protein denaturation by combined effect of shear and air-liquid interface. Biotechnol. Bioeng. 54, 503-12 (1997).3. Henson, A. F., Mitchell, J. R. & Mussellwhite, P. R. The surface coagulation of proteins during shaking. J. Colloid Interface Sci. 32, 162-165 (1970).4. Mahler, H.-C., Senner, F., Maeder, K. & Mueller, R. Surface Activity of a Monoclonal Antibody. J. Pharm. Sci. 98, 4525-4533 (2009).5. Weiss, W. F., Young, T. M. & Roberts, C. J. Principles, approaches, and challenges for predicting protein aggregation rates and shelf life. J. Pharm. Sci. 98, 1246-1277 (2009).6. Kerwin, B. A. Polysorbates 20 and 80 Used in the Formulation of Protein Biotherapeutics:Structure and Degradation Pathways. J. Pharm. Sci. 97, 2924-2935 (2008).7. Chennamsetty, N., Voynov, V., Kayser, V., Helk, B. & Trout, B. L. Design of therapeutic proteins with enhanced stability. Proc. Natl. Acad. Sci. 106, 11937-11942 (2009).

CSSS 42

Measurement of surface tension and viscoelastic parameter values in ultra-thin liquid crystal films at the air/water interface

N. K. Thapa1, H. A. Alwusaydi1, A. E. Smart2, W. V. Meyer3, A. I. Belgovskiy4, J. A. Mann, Jr.5, E. K. Mann1. 1Physics, Kent State University, Kent, OH, 2Scattering Solutions, Inc., Costa Mesa, CA, 3Scattering Solutions, Inc., Kent State University, Cleveland, OH, 4Scattering Solutions, Inc., Cleveland, OH, 5Chemical Engineering, Case Western Reserve University, Cleveland, OH. Email: nthapa@kent.edu

Thermally excited capillary waves (ripplons) with an rms height ~1 nm exist on a fluid/liquid interface. The capillary wave dispersion equation relates surface properties, such as surface tension and surface viscoelasticity, to what can be measured using Surface Light Scattering Spectroscopy (SLSS) [1-3]. At a fixed wave vector, the Doppler spectrum of light scattered is sensitive to these surface properties. Historically, unambiguous determinations of some surface properties have been difficult. A superior optical set-up enables us to obtain clean signals for wave vectors much higher than previously possible. We can now access a regime where the dispersion relation is more sensitive to the surface viscoelastic parameters. We describe this enhanced technique and present measurements of viscoelastic properties determined for molecularly-thin 8CB (4-Octyl-4-biphenylcarbonitrile) liquid crystal films at the air/water interface. We report the change of viscoelastic parameter values over a temperature range where phase changes of the liquid crystal go from smectic through nematic to isotropic.References:[1] D. Langevin Light Scattering by Liquid Surfaces and Complementary Techniques (Surfactant Science) (CRC Press, 1991).[2] W.V. Meyer, et al Advances in surface light scattering instrumentation and analysis: non-invasively measuring of surface tension, viscosity, and other interfacial parameters, Appl. Opt. 40, 4113 (2001).[3] J.A. Mann, Jr et al., Surface fluctuation spectroscopy by surface light scattering spectroscopy, Appl. Opt. 40, 4092 (2001).

CSSS 43

Phase behavior and rheology of disperse colloid-polymer mixtures

J. Conrad. University of Houston, Houston, TX. Email: jcconrad@uh.edu

Mixtures of microscale particles and non-adsorbing polymers are employed to study the phase behavior and properties of attractive colloidal suspensions, which are widely used in materials shaping and forming processes, including three-dimensional printing and nanocomposite processing, and in technical applications as paints, coatings, inks, and drilling muds. In addition, these suspensions serve as simple physical models in which to explore aggregation within crowded, confined biological settings. Polymer constituents of high dispersity in size and molecular weight are inexpensive and hence widely used in industrial settings; likewise, the broad distribution of macromolecules found within cells leads to high size dispersity. Fundamentally, the effects of polymer size dispersity on the aggregation and flow properties of colloid-polymer mixtures are incompletely understood. Here, I will highlight our recent studies exploring the effects of polymer dispersity on the non-equilibrium phase behavior, microstructure, and rheology of depletion mixtures of colloids and polymers. The gelation transition from an equilibrium fluid to a non-equilibrium gel in quiescent conditions can be mostly understood using an effective polymer concentration that accounts for distributions in molecular weight. These mixtures, however, shear-thicken and exhibit positive first normal stress differences, which are somewhat unexpected for particulate suspensions with effective interparticle attractions.

CSSS 44

First normal stress differences of attractive model colloid + polymer mixtures

N. Park, J. C. Conrad. Chemical and Biomolecular Engineering, University of Houston, Houston, TX. Email: nykim@uh.edu

Non-zero normal stress differences often contribute significantly to the processability of materials. For instance, bulk physical phenomena in complex fluids such as rod climbing and dye swell are driven by a nonzero first normal stress difference N1. For shear-thickening suspensions of hard-sphere particles, the emerging understanding is that lubrication forces lead to negative N1 whereas frictional forces lead to positive N1. Polymers added to hard-sphere colloidal suspensions, however, can give rise to attractive interactions that alter the phase behavior of the particles. These attractions may be weak depletion attractions or stronger bridging attractions, depending on whether the polymers adsorb on the surface of the particles. How these different types of polymer-mediated attractions affect N1 is not well understood. Prior studies suggest that attractive interactions may eliminate shear thickening, but there is not yet a consensus on the effect of attractions on the sign of N1. It is also possible that polymer-mediated attractive colloids would follow the behavior of non-attractive suspensions in polymer media, which exhibit pronounced nonzero N1 due to the presence of the polymer. Here, we measured the rheology (viscosity and N1) of attractive colloidal suspensions with depletion and bridging attractions. Co-polymer particles of 2,2,2-trifluoroethyl methacrylate and tert-butyl methacrylate [T. E. Kodger et al., Sci. Rep., 5, 14635 (2015)] were suspended at volume fraction = 0.40 in a refractive index- and density-matched mixture of glycerol and water, with 20 mM NaCl added to screen electrostatic charges. To these suspensions, we added poly(acrylamide) or poly(acrylic acid) to induce depletion or bridging attractions, respectively. The shear-rate dependent viscosity and N1 were measured and analyzed for each set of samples with increasing concentration of polymer, corresponding to stronger attraction strengths. Significantly different rheology resulted by simply changing the polymer additive in suspensions with same particles, particle volume fraction, salt, and solvent. These results suggest that processability of suspensions may be tuned by changing the type of polymer additive used in formulations.

CSSS 45

Excess entropy scaling law in two-dimensional "attractive" colloidal fluids

X. MA1, J. LIU1, Y. Zhang2, P. Habdas3, A. G. Yodh1. 1Physics & Astronomy, University of Pennsylvania, Philadelphia, PA, 2Physics, Peking University, Beijing, CHINA, 3Physics, Saint Joseph's University, Philadelphia, PA. Email: xiaom@seas.upenn.edu

Using optical microscopy and video tracking techniques, we measure the structure and diffusion dynamics of colloidal particles in quasi-two-dimensional colloidal fluids with short-range attractive interactions. The attraction is induced by the rod-like surfactant (C12E6) micelles and can be tuned by temperature. We collect particle trajectories from different packing fractions and attraction strength. From the trajectory data, we calculate the pair correlation functions g(r) and the two-body excess entropy S2. The structure is found more ordered when attraction is stronger at fixed packing fraction. We then measure the mean square displacement and long-time diffusion coefficient D. The diffusion dynamics is found slower with stronger attraction. Finally, we show that the normalized diffusion coefficient follows the excess entropy scaling, D*=exp(cS2), with the prepactor c=0.85, for various attraction strengths and packing fractions. (Work is supported by NSF DMR16-07378, PENN MRSEC DMR17-20530, and NASA NNX08AO0G)

CSSS 46

Direct investigation of microstructure dynamics during drying of colloid-