Aem Lect11

Advanced Electronic Ceramics I (2004)

Zeta potential : Definition

http://www.zeta-meter.com/

Strongly bounded layer

Additional positive ions are still attracted by the negative colloid, but now they are repelled by the Stern layer as well as other positive ions that are trying to approach the colloid- dynamic equilibrium

results in diffuse layer

♦ Zeta potential : the potential at the shear plane♦ Why Zeta potential for the stable colloid? the interaction of the particles in polar liquids is

not governed by the surface potential but by zeta potential

Electric double layer= Stern layer + Diffuse Layer


Zeta potential: ξ♦ ξ : potential at the surface of shear♦ the surface of shear : the boundary between the

immobilized layer and the mobile fluid♦ ξ is not always coincident to Stern potential (ψδ)- besides the specifically adsorbed layer(Stern layer),

the more immobilized layer can be formed- however, usually ξ ≈ ψδ(it means the Stern surface is usually coincident to the surface of shear)

♦ why important?various motions such as Brownian motion andsedimentation which affect thestability of colloid are determined by this potential


Electrophoresis

Electrophoresis : Moving of charged particle in a dispersion under the electric filed

Fel = q E

Fvis = f v

at stationarystatev = q E / f

= q E /(6πηR)= zeE/(6πηR)

u = v / E

E : electric field (V/m)Fel : the force that an isolated ion experiences by E Fvis : opposing force due to the viscous mediumf : friction factor

from the Stokes law f = 6πηRR : is the radius of the particlev : velocity of the particlez : valence of the ione : electron chargeu : electrophoretic mobility


Electrophoresis

Hückel approximation

ξ = 3ηu/2ε= q / (6πεR)

κR < 0.1

R is small compared to κ-1

κ-1 is largeionic strength(I) smallnon-aqueous media

Helmholtz-Smoluchowskiapproximation

ξ = ηu/ε=q / (4πεR)

κR > 100

R is large compared to κ-1

κ-1 is smallhigh concentration of electrolytepolar aqueous solution


Electrophoresis


- The effective particle surface charge in a liquid-solid sample is measured by the application of a preset constant electric current applied across the suspension. By determining the rate at which particles migrate into or out of a sample cell (electrophoretic mobility), zeta potential measurement is obtained. This measurement is typically performed over a range of different conditions to optimize the influence of one or more variables.

- A rotating chamber eliminates the settling of coarse particles and minimizes thermal

current effects.

http://www.micromeritics.com/

Zeta Potential


Zeta Potential

Dark-field illumination

Www.zeta-meter.com


Experimental aspect of electrophoresis

1. Error coming from sedimentation can be corrected by comparing the result with that under no electric field

2. Convection - working at low current, effective thermostating3. Electro-osmotic effect- moving liquid relative to the stationary chamber

Stationary layer(no Electro-osmotic effect)


Laser Doppler Velocimetry

Laser Doppler Velocimetry (LDV).Moving particles in the measurement zone shift the frequency of scattered light proportional to their velocity.the particle image ⇒ the illumination of particles by intersecting laser beamsthe observer’s eye ⇒ the photomultiplierthe stopwatch ⇒ the correlator.

Advantage for LDV- Statistically better measurements - Seconds measurement time rather than 10-30 minutes

- Measurement of smaller particles, 5-10nm rather than a minimum of 200nm

- Measurement of zeta potential distributions - Improvement in measurement repeatability

due to a reduction in the Joule heating effect

http://www.silver-colloids.com/Tutorials/Intro/zetaintro.html


Laser illumination and video interface allows submicronic particle measurement.

1. The cell consists of two pairs of palladium electrodes fitted into perfectly symmetrical, high quality Suprasil Quartz chambers

2. Easy to clean: a kinematics mounting gives easy access to the measuring chamber

3. The mounting allows rapid and precise positioning of the cell after cleaning

4. Replaceable main electrodes 5. Sample temperature is permanently

measured in-situ by fast response micro-probe

http://www.lavallab.com/eng/zeta-eng/zeta-meter.htm

Microelectrophoresis


Zeta-potential : application

1. Sewage treatment2. Paints3. Printing Ink4. Monitor for flocculation5. Slip casting

Www.zeta-meter.com


Display


E-paper & E-ink

Micrograph of electronic ink, a bistable and printable microencaspulated electrophoretic display material created in MIT media lab and currently being developed at E Ink Corp.http://www.media.mit.edu/nanomedia/index.html http://www.eink.com/pdf/key_benefits.pdf

B Comiskey, JD Albert, H Yoshizawa, J Jacobson, Nature 394 (6690) 253-255 1998

Advanced Electronic Ceramics I (2004)J.A.Rogers, MRS Bulletin, 26(7), 530 (2001)

Figure Step for fabricating organic transistors and circuits. Microcontact printing (µCP) with a cylinderical stamp provides a fast, low-cost method to produce high-resolution source/drain electrodes and interconnects. SAM stands for self-assembled monolayer.

Principle & Fabrication

Advanced Electronic Ceramics I (2004)J.A.Rogers, MRS Bulletin, 26(7), 530 (2001)

Extended View and Example


Principle

http://www.eink.com/technology/index.htm

The balls(called as ‘gyricon’) are about the size of a dot made with a very fine pen. Inside each one is another, smaller sphere, half white and half black, suspended in oily silicon so that it can rotate freely. The black half of the inner sphere is positively charged, while the white half is negatively charged. When an electronic charge is applied to the sheet of e-paper (using a special printer attached to a computer, or a hand-held scanning device), the inner sphere rotates to show either its white half or black half, according to the print instruction. The result is a black-and-white image.


Very thin

http://www.eink.com/news/releases/pr60.html

E Ink Corporation of Cambridge, Mass. has introduced the world's thinnest active matrix display that is just 0.3 mm thick, or half the thickness of a credit card. The company is working with leading device makers to integrate these ultra-thin electronic ink displays into next generation portable devices by 2004-2005.


Benefits1. Paper-like readability2. Write using electronic stylus(can be stored and sent via email)3. Cheaper and more flexible than LCDs4. Low power

http://www.eink.com/solutions/appliances.htm


TiO2 nanotube

K.Subramanya et al., Nano Letters, 1, 727 (2001)

Layer-by-layer-colloid-templating(LbL-CT approach)

The surface charge reversal at the end of each deposition cycles

ξ bare Ni rods: -48 mVξ after PDADMAC: +40mVξ After PSS: -30mV

ξ After PDADMAC: +30mVξ After TALH: -25 mV

TALH: Titanium bis ammonium lactato dihydroxide

PDADMAC: poly diallyldimethylammonium chloride


TiO2 nanotube

K.Subramanya et al., Nano Letters, 1, 727 (2001)

Technology

Aem Lect11