ABSTRACT
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
II. The Electrical Double Layer around a Colloid Particle . . . . . . . . . . . . . . . . . . . . . . 44
III. Electrokinetic Phenomena and the Zeta Potential . . . . . . . . . . . . . . . . . . . . . . . . . . 48
IV. Electrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A. Physical Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
B. Experimental Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
1. Microelectrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2. Electrophoretic Light Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
V. Sedimentation Potential (Dorn Effect) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
VI. Dielectrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
VII. Low-Frequency Dielectric Dispersion of Suspensions . . . . . . . . . . . . . . . . . . . . . . . 62
A. Physical Bases for the Dielectric Relaxation in
Suspensions of Colloidal Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
B. The Measurement of the Dielectric Constant of Suspensions . . . . . . . . . . . . . . . 64
VIII. Electroacoustic Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
IX. Electrokinetics of Nonrigid Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
X. Dynamic Stern Layer and Electrokinetic Phenomena . . . . . . . . . . . . . . . . . . . . . . . . 72
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Everybody involved in the use, design, or investigation of colloidal particles dispersed in aqueous
solution is aware of the importance of the surface charge acquired by the particles. Many properties
of the suspension are in fact dramatically controlled by the large surface-to-volume ratio of the par-
ticles and by the additional phenomenon of charging of the interface. With respect to the first issue,
recall that while a spherical particle 1 cm in diameter has a surface-to-volume ratio of 600 m21, the
figure increases by as much as a factor of 104 if the same particle was subdivided into 1-mm particles. But it is the second issue mentioned (the existence of the charged interface) that is the core of
this chapter. Figure 3.1 shows approximately the stability ratio of charged spheres 100 nm in diam-
eter suspended in 1 mmol/l KCl solutions. This quantity is the ratio of the number of collisions between particles to the number of collisions resulting in coagulation, and it measures how
effective is the surface charge to avoid aggregation in the suspension. Note the dramatic effect
of the surface charge on the colloidal stability of the system: it increases by orders of magnitude
even for the relatively modest charges accessible to the colloidal particles.
