FIELD DEPENDENCE OF PARTICLE ELECTROPHORETIC MOBILITY IN NONPOLAR LIQUIDS

Contrary to earlier thought, recent studies have shown that particle electrophoretic mobility in nonpolar liquids is dependent on field strength at high fields. This study provides independent confirmation using a cross-flow electrofiltration technique and explores possible explanations for the phenomena. Experimental work was conducted using kaolin/Mi1-H-5606A petroleum oil systems with various concentrations of ionic additive. Electrophoretic mobility at different field strengths and additive concentrations were determined. It was found that mobility is independent of field strength at low and high fields but varies with field strength at intermediate fields. This dependence is explained on the basis of the relaxation effect and partial detachment of the diffuse double layer from the particle. In the field dependent region the mobility change with respect to field Increases with increasing surface charge and electrical double layer thickness. At high fields the double layer completely detaches and mobility behaves independently of field strength. Prior exposure of the particle to high fields appeared to temporarily increase mobility. This may be the result of selective deposition of low mobility particles and Increased particle charge due to field charge exchange or contact charging. Under the conditions of this study double layer detachment appeared to be the major source of field dependent behavior.