On the other hand, the systems normally used, as de-An experimental investigation of the electrokinetic transport of scribed in the literature, cannot simply be considered as negative and positive polystyrene beads in alcohol-water mixtures colloidal model systems. In this sense, monodisperse spheriis described. The electrophoretic phenomenological coefficient has cal polystyrene latexes have proved to be very useful model been measured, and a nonlinear dependence on the alcohol concensystems for testing the most recent electrokinetic theories tration has been found. The liquid properties (density, viscosity, (13,14). As most of the theories deal with spherically and dielectric constant) and the z-potential have been shown to shaped particles of identical size, the introduction of monoplay a significant role in the internal structure of the electrophodisperse latexes appeared to offer excellent chances for the retic coefficient (l 21 ) for the negative polystyrene/(ethanol or 1experimental verification of these theories. However, in the propanol) -water mixture. This behavior is quite different for positive polystyrene. A typical hydrophobic character of the positive last years, growing evidence of an anomalous electrokinetic polystyrene contrast with the double hydrophobic-hydrophilic behavior of this system has appeared in the literature (15character of the negative one. ᭧ 1998 Academic Press 22). It has been found that electrophoretic mobility curves Key Words: electrokinetic coefficients; polystyrene; liquid pass through a maximum as a function of increasing ionic mixtures.
strength, opposite to that expected. Various explanations for this maximum have been proposed (16)(17)(18). One based upon the existence of an additional surface conductance