advertisement

Electrokinetics of colloids

100 %
0 %
advertisement
Information about Electrokinetics of colloids
Education

Published on March 24, 2009

Author: amitmgupta31

Source: authorstream.com

advertisement

Slide 1: Electro-kinetics of Colloids Slide 2: DEFINITION OF A COLLOID Ostwald: “die Welt der vernachlässigten Dimensionen” Chem E 455: Surface and Colloid Science Laboratory: Autumn and Spring Quarters Slide 3: LYOPHOBIC COLLOIDS Slide 4: INSTABILITY OF LYOPHOBIC COLLOIDS Slide 5: LONG-RANGE VAN DER WAALS ATTRACTION s0 a Slide 6: ELECTROSTATIC REPULSION RETARDS AGGREGATION van der Waals attraction Slide 7: ELECTRICAL CHARGE AT AQUEOUS INTERFACES Slide 8: ELECTRICAL DOUBLE LAYER Slide 9: THE GUOY-CHAPMAN DOUBLE LAYER Slide 10: Poisson equation (describes variation of potential in a spatial charge distribution) Boltzmann equation (describes variation of ion concentration in an electric field) Slide 11: For a single, symmetric (z-z) electrolyte… for low potentials |z?0| = 25 mV, sinh y ˜ y, and “Debye-Hückel approximation” Slide 12: ION CONCENTRATION PROFILES “Double layer thickness” Slide 13: EFFECT OF ELECTROLYTE CONCENTRATION ON DOUBLE LAYER THICKNESS Slide 14: REFINEMENTS OF DOUBLE LAYER MODEL Slide 16: STERN MODEL (1924) ? ?? ?0 ?(x) Surface potential Stern potential Stern layer Stern layer thickness Slide 17: STRONG SPECIFIC ADSORPTION IN THE STERN LAYER Slide 18: ELECTROSTATIC REPULSION DEPENDS ON…. The Stern potential, ?? The thickness of the diffuse double layer, ?-1 Slide 19: Forces between particles (surfaces) s When (?/kT) ? 10, ? “stability” Derjaguin Landau Verwey Overbeek Slide 20: Controlling DLVO interactions Slide 21: Controlling electrolyte valence and concentration For z =2, divide all C’s by 64; for z =3, divide all C’s by 729 Slide 22: a = 0.1mm; T=298K; A212=10-19J; k-1=33Å; e=78.5 Controlling effective Stern potential, yd Slide 23: HOW CAN WE MEASURE THE STERN POTENTIAL? Slide 24: ELECTROKINETIC EFFECTS Electro-osmosis V (electro-osmotic velocity) Slide 25: ELECTROPHORESIS Vp = electrophoretic velocity Relevant to colloidal dispersions Slide 26: I. Externally imposed EMF produces motion 1. Liquid moves; solid is stationary 2. Solid moves; liquid is stationary II. Externally imposed motion produces EMF 1. Liquid forced to move past solid 2. Solid forced to move through liquid THE ELECTROKINETIC EFFECTS Slide 27: At steady state: ?E = streaming potential i = streaming current Slide 28: I. Externally imposed EMF produces motion 1. Liquid moves; solid is stationary 2. Solid moves; liquid is stationary II. Externally imposed motion produces EMF 1. Liquid forced to move past solid 2. Solid forced to move through liquid THE ELECTROKINETIC EFFECTS Slide 29: “Dorn Effect” Slide 30: Electro-osmosis Slide 31: Integrating once: Slide 32: Measurement of electro-osmotic velocity Typically, V ˜ a few mm/min Slide 33: INTERPRETATION OF THE ZETA POTENTIAL Slide 34: ELECTROPHORESIS Vp = electrophoretic velocity Slide 35: MEASURING ? BY MICRO-ELECROPHORESIS Electrophoretic mobility Slide 36: The measurement of electrophoretic mobility Rank Brothers Mark II Microelectrophoresis System FLOW CELL + Slide 37: and vx = 0 at y = 0.2113w and 0.7887w Slide 38: RELATING MEASURED uE TO ZETA POTENTIAL When double layer is thin relative to particle radius: ?a > 300 a ?-1 When double layer is thick relative to particle radius: ?a < 0.1 Slide 39: Spherical particles; 1-1 electrolyte Hückel Smoluchowski Slide 40: Polyvalent electrolytes C(?a) ?a Slide 41: Some ion properties* * Moelwyn-Hughes, E.A., Physical Chemistry, 2nd Ed., p. 859, Pergamon Pr., Oxford, 1961. Slide 42: Approximate solution for symmetric (z-z) electrolytes* *O’Brien, R.W., and Hunter, R.J., Can. J. Chem., 59, 1878 (1981). Good to order (?a)-1 Slide 43: Aqueous KNO3 solutions, 25°C Slide 44: Pen Kem Model 501 Lazer Zee Meter™ Slide 45: ZETA POTENTIAL AS A QC VARIABLE FOR WASTEWATER TREATMENT Slide 46: MORE MODERN METHODS FOR MEASURING ELECTROPHORESIS Based on light scattering techniques Slide 47: Quasi-elastic light scattering (QELS) Doppler shift in frequency (line broadening) of scattered light due to particle motion A = instrument constant D = particle diffusivity Q = magnitude of the scattering vector Measure ?w ? D ? particle size But ?w ˜ 103 Hz and w0 ˜ 1016 Hz Slide 48: Heterodyning Slide 49: Electrophoretic quasi-elastic light scattering Shifted autocorrelation function Slide 50: Photon Correlation Spectroscopy (PCS) Intensity pair autocorrelation function homodyning Electrophoretic PCS Slide 51: Laser Doppler Electrophoresis (LDE) + _

Add a comment

Related presentations

Related pages

CHE Seminar Series: Interparticle Forces, Hydrodynamics ...

CHE Seminar Series: Interparticle Forces, Hydrodynamics and Electrokinetics of Nontraditional Colloids: the Case of Carbon Nanotubes and Janus Particles
Read more

AC Electrokinetics: Colloids and Nanoparticles, 2003, 324 ...

AC Electrokinetics: Colloids and Nanoparticles, 2003, 324 pages, Hywel Morgan, Nicolas G. Green, 0863802559, 9780863802553, Research Studies Press, 2003
Read more

Electrokinetics - Polymer Colloids - Chapter 8

This chapter deals with electrokinetics. It describes a flat electrical double layer in terms of a negatively charged surface with small, positive ...
Read more

AC electrokinetics: colloids and nanoparticles - Enlighten ...

Morgan, H., and Green, N.G. (2003) AC electrokinetics: colloids and nanoparticles. Series: Microtechnologies and microsystems series.
Read more

Electrokinetics on superhydrophobic surfaces - IOPscience

Electrokinetics on superhydrophobic surfaces. ... the mobilities of colloids on a ... that might affect the electrokinetics in the following for ...
Read more

Electrokinetics on superhydrophobic surfaces

Electrokinetics on superhydrophobic surfaces Periklis Papadopoulos1, Xu Deng1,2, Doris Vollmer1 and ... the mobilities of colloids on a negatively
Read more

Electrokinetic phenomena - Wikipedia, the free encyclopedia

Electrokinetic phenomena are a family of several different effects that occur in heterogeneous fluids, or in porous bodies filled with fluid, or in a fast ...
Read more

AC Electrokinetics: Colloids and Nanoparticles ...

Hywel Morgan - AC Electrokinetics: Colloids and Nanoparticles (Microtechnologies and Microsystems) jetzt kaufen. ISBN: 9780863802553, Fremdsprachige ...
Read more

Colloids in external electric and magnetic fields ...

EPJ. a; b; d; e; ap; st; h; plus; c; ds; pv; nbp; ti; qt; am; n; woc; ... Electrokinetics is studied for colloids in confinement, where the confining walls ...
Read more

AC Electrokinetic: Colloids and Nanoparticles

AC Electrokinetic: Colloids and Nanoparticles on ResearchGate, the professional network for scientists.
Read more