1. Electrokinetic Theory Study of moving charged particles and their interactions with electric fields. 4 general types of phenomenon Electrophoresis applying a field moves a charged particle Sedimentation potential opposite effect: moving particles create the field

2. Electro-osmosis movement of a liquid (containing aqueous ions) with respect to a charged surface in a field. Streaming Potential opposite effect: the moving liquid now creates the field

3. What can we measure? Mobility (u): how fast the particle moves (v) in an applied field, E. u=v/E Need to relate this to properties of the colloidal particles: charge, surface potential, and size. For a point particle q=ze For a colloid though, a large particle does not act like a point particle, so we must consider the surface potential.

4. Zeta Potential Potential at the surface of shear between charged surface and the liquid layer We assume that  and the Stern Potential   are approximately the same static moving

5. No longer are we concerned with a simple surface either: we assume that the charged particles are spheres  R s small Huckel limit  R s large Helmholtz- Smoluchowski limit

6. Huckel Limit (  R S small) (see Hiemenz and Rajagopalan) Want a relationship between q and  A general expression for the electric field is given by Coulomb’s law:  Since... Huckel Equation valid for  R S < 0.1 s ss ss R4 q )R1(R4 q )/1R(4 q R4 q       

7. Helmholtz-Smoluchowski Equation (  R S large)

8. Helmholtz- Smoluchowski Equation valid for  R S > 100

9. Henry’s Equation

10. Assumptions spherical particles low field conditions (D-H approximation) non-conducting particles double layer undistorted by flow (relaxation effect) + E + -

12. Surface Charge and Zeta Potential Recall from our discussion of the Huckel limit that... Again… spherical particles low field limit

13. Experimental Techniques Particle Electrophoresis

14. Electro-osmotic effects can also cause difficulties in interpretation.