STREAMING CURRENT OF POLYSTYRENE POROUS PLUGS - SOLVENT COMPOSITION EFFECT

The main purpose of this work is to research the solvent composition e ffect on the streaming current of porous plug formed by monodisperse p olystyrene microspheres. Polystyrene was selected as the disperse mate rial because monodisperse, spherical polystyrene latexes have proved t o be useful model systems, whose surface charge density can be conveni ently controlled. A polystyrene latex was prepared by emulsifier-free emulsion polymerization, having a particle size of 1.2 mu m and a surf ace charge density of -34.0 +/- 1.0 mC/m(2). Binary mixtures of ethano l-and l-propanol-water were used to understand the effect of the liqui d phase composition on the streaming current of polystyrene porous plu gs. For the ethanol- and l-propanol-water mixtures the streaming curre nt depends nonlinearly on the molar alcohol fraction, This nonlinear d ependence can be explained by the variation of the viscosity and diele ctric permittivity of the liquid with solvent composition. The zeta-po tential plays also an important role in the explanation of the above d ependence, especially with binary mixtures low in alcohol where a mini mum in the zeta-potential appears. The electrokinetic results obtained in this work suggest that the basically hydrophobic polystyrene surfa ce is modified by the presence of hydrophilic sites. Adsorption of alc ohol molecules on the charged hydrophilic sites leads to desorption of counterions from the inner part of the electrical double layer. (C) 1 998 Academic Press.