1. Zeta potential : Definition
♦ 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
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
Strongly bounded layer
Electric double layer
= Stern layer + Diffuse Layer
http://www.zeta-meter.com/
Advanced Electronic Ceramics I (2004)
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 and
sedimentation which affect the
stability of colloid are
determined by this potential
Advanced Electronic Ceramics I (2004)
2. Electrophoresis
Electrophoresis : Moving of charged particle in a dispersion
under the electric filed
E : electric field (V/m)
Fel = q E
Fel : the force that an isolated ion experiences by E
Fvis : opposing force due to the viscous medium
Fvis = f v
f : friction factor
from the Stokes law f = 6πηR
at stationary
R : is the radius of the particle
state
v : velocity of the particle
v=qE/f
z : valence of the ion
= q E /(6πηR)
e : electron charge
= zeE/(6πηR)
u : electrophoretic mobility
u=v/E
Advanced Electronic Ceramics I (2004)
Electrophoresis
Hückel Helmholtz-Smoluchowski
approximation approximation
ξ = 3ηu/2ε ξ = ηu/ε
= q / (6πεR) =q / (4πεR)
κR < 0.1 κR > 100
R is small compared to κ-1 R is large compared to κ-1
κ-1 is large κ-1 is small
ionic strength(I) small high concentration of electrolyte
non-aqueous media polar aqueous solution
Advanced Electronic Ceramics I (2004)
3. Electrophoresis
Advanced Electronic Ceramics I (2004)
Zeta Potential
- 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/
Advanced Electronic Ceramics I (2004)
4. Zeta Potential
Dark-field illumination
Www.zeta-meter.com
Advanced Electronic Ceramics I (2004)
Experimental aspect of electrophoresis
Stationary layer
(no Electro-osmotic
effect)
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 thermostating
3. Electro-osmotic effect
- moving liquid relative to the stationary chamber
Advanced Electronic Ceramics I (2004)
5. 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 beams
the observer’s eye ⇒ the photomultiplier
the 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
Advanced Electronic Ceramics I (2004)
Microelectrophoresis
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
Advanced Electronic Ceramics I (2004)
7. 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)
Principle & Fabrication
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.
J.A.Rogers, MRS Bulletin, 26(7), 530 (2001)
Advanced Electronic Ceramics I (2004)
8. Extended View and Example
J.A.Rogers, MRS Bulletin, 26(7), 530 (2001)
Advanced Electronic Ceramics I (2004)
Principle
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.
http://www.eink.com/technology/index.htm
Advanced Electronic Ceramics I (2004)
9. Very thin
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.
http://www.eink.com/news/releases/pr60.html
Advanced Electronic Ceramics I (2004)
Benefits
1. Paper-like readability
2. Write using electronic stylus(can be stored and sent via email)
3. Cheaper and more flexible than LCDs
4. Low power
http://www.eink.com/solutions/appliances.htm
Advanced Electronic Ceramics I (2004)
10. TiO2 nanotube
Layer-by-layer-colloid-templating
(LbL-CT approach)
The surface charge reversal at the
end of each deposition cycles
ξ bare Ni rods: -48 mV
ξ after PDADMAC: +40mV
ξ After PSS: -30mV
ξ After PDADMAC: +30mV
ξ After TALH: -25 mV
TALH: Titanium bis ammonium
lactato dihydroxide
PDADMAC: poly
diallyldimethylammonium chloride
K.Subramanya et al., Nano Letters, 1, 727 (2001)
Advanced Electronic Ceramics I (2004)
TiO2 nanotube
K.Subramanya et al., Nano Letters, 1,
727 (2001)
Advanced Electronic Ceramics I (2004)
