MWN for the Study of Macromolecular Ferrofluids

Judy S. Riffle, Virginia Polytechnic Institute and State University, DMR 0602932

PDMS MW g mol-1 Wt % Magnetite DLS Dn (nm) Model Dn (nm)3,000 44 19 175,000 42 22 217,000 38 24 2410,000 41 23 26

PDMS-Magnetite nanostructures have been rationally designed to form neat ferrofluids that can be remotely manipulated with magnetic fields. We have a modeling tool for calculating the sizes of sterically-stabilized single-particle complexes to an accuracy within 10%. Using a modified DLVO theory for particle interactions, this tool also predicts the onset of colloidal instability in these magnetic suspensions.

Top figure: A representative TEM image shows a well-defined magnetite core. Bottom figure: Particle histograms of repeated magnetite syntheses show a high degree of reproducibility. Table: Comparison of number average diameters Dn from dynamic light scattering (DLS) with those predicted by the model, with no adjustable parameters, show excellent agreement.

Remote Shape Control of Macromolecular Ferrofluid Droplets Judy S. Riffle, Virginia Polytechnic Institute and State University, DMR 0602932

The Materials World Network for the Study of Macromolecular Ferrofluids addresses the chemistry, engineering and physics that govern remote control over the shapes and locations of magnetic droplets suspended in immiscible media. Top: Raquel Mejia-Ariza (left, VT student) and Annette Tyler (right, UWA student) collaborate at VT to understand the influence of interfacial tension on the shapes of magnetic PDMS droplets in uniform magnetic fields. Bottom: Droplet shape in uniform fields results from a balance between particle alignment induced by the field and interfacial energy.

1. S. Afkhami, Y. Renardy, M. Renardy, J.S. Riffle, T.G. St. Pierre, J. Fluid Mechanics, 610, 363-80 (2008). 2. O.T. Mefford, M.L. Vadala, M.R.J. Carroll, R. Mejia-Ariza, B.L. Caba, T.G. St. Pierre, R.C. Woodward, R.M. Davis, J.S. Riffle, Langmuir, 24(9), 5060-69 (2008).