Transcript Zeta potential measurement - Plymouth State University

Zeta potential measurement
Introduction
• Zeta potential is the charge that is located at the
slipping point of a particle in a medium.
• Zeta potential is used mostly in Colloidal
chemistry.
• If the magnitude of zeta potential is > 30mV then
it is in stable suspension
• pH has a major effect on the system
• Zeta potential can not be calculated directly.
• However using Electro kinetic effects zeta
potential can be measured
Zeta Potential system(general)
• He/Ne laser, goes to a beam splitter which
then sends the beam to a fixed mirror and a
modulator.
• Then the beams head into the sample with an
electrode on both ends.
• Then a photomultiplier picks up the signal and
sends it to a computer.
Electro Kinetic Effects
• Electro kinetic potential is caused by the
interfacial double layer within a solution.
• The double layer has a stern layer and a
diffuse layer.
• Using an electric field either electrophoresis
or electro osmosis will cause the particles to
move
Electrophoresis
• Under an applied electric field the movement
of charged particles in relation to the liquid its
suspended in is measured
• The velocity of the movement depends on the
strength of the field, dielectric constant,
viscocity, and zeta potential
• Using Henry’s law zeta potential can be
measured
Electrophoresis (Cont.)
• Measurement of electrophoretic movement
• Laser Doppler Velocimetry(LDV)
Electro Osmosis
• Movement of charged particles relative to a
stationary charged surface
• Similar to electrophoresis an electric field is
applied and the charged particles begin to
move.
• A reverse flow is used to counter the flow of
the liquid system when the field is applied
Electro Osmosis (Cont.)
• One problem is that there is only two places
where there is truly the electro osmosis effect
• M3 measurment-Using LDV
• Slow Field Reversal (SFR)
• Fast Field Reversal (FFR)
Zeta Potential uses
• Zeta potential can be used as a means to tell
how stable a colloid being analyzed is.
• Zeta potential is key to understanding
dispersion and aggregation processes in water
purification, ceramic slip casting and the
formation of inks, paints and cosmetics.
• Often the only way to charecterize double
layer properties
Benefits
• A good way to find the
characteristics of the double
layer in a colloidal mixture.
• This also allows you to see
how stable the colloid being
analyzed is.
Limitations
• Zeta Potential can not be
directly measured.
• When finding the Zeta
Potential the size of the
double layer must be very
thin.
Works Cited
• Zeta Potential Overview, Brookhaven Instruments, 1, 2009
• Lyklema, J. Fundamentals of Interface and Colloid Science,
vol.2, page.3.208, 1995
• The Zeta Potential, Colloidal Dynamics, 4, 1999
• Zeta Potential Introduction, Nicomp 380 ZLS, 101, 2006
• IUPAC Technical Support. Measurement and Interpretation of
Electrokinetic Phenomena, vol.77, pp.1753-1805.2005
• Zeta Potential theory, pp.16.1-16.12.2005
• http://www.silver-colloids.com/Tutorials/Intro/pcs1.html