8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.89Concentration dependent electrophoretic mobility ofcharged colloids at low ionic strength measured withlaser-Doppler and acoustic electrophoresisRob Kortschot, 1 Albert Philipse, 1 and Ben Erné 11 Utrecht University, Van ’t Hoff Laboratorium for Physical and Colloid Chemistry,Padualaan 8, 3583CH, Utrecht, NetherlandsElectrophoresis is often used to determine the charge of colloids from measurements of the electrophoreticmobility. Usually, the analysis assumes that the particles do not influence each other’smotion as long as the colloidal concentration is low. However, at low ionic strength, the dynamicsof charged colloids is virtually always strongly concentration dependent, as indicated by sedimentationvelocity measurements [1]. In such cases, determination of the charge of colloids fromelectrophoretic mobility is no longer straightforward, as colloidal interactions must be taken intoaccount. We measured the electrophoretic mobility of a well-characterized model system of TPMcoatedsilica particles in ethanol [2] as a function of concentration and ionic strength with twoindependent techniques: laser-Doppler and acoustic electrophoresis. Laser-Doppler electrophoresisdirectly detects particle motion in an external electric field directly using light scattering, butit is limited to low concentrations to prevent multiple scattering. Acoustic electrophoresis employssound to move the colloids and indirectly measures the mobility from the resulting electricalcurrent, which can be done at high concentrations. The strengths and limitations of the two techniqueswill be discussed and conclusions will be drawn about the electrophoretic mobility at lowionic strength.[1] D. M. E. Thies-Weesie, A. P. Philipse, G. Nagele, B. Mandl and R. Klein, J. Colloid; InterfaceSci. 176 (1995) 43-54[2] A. P. Philipse and A. Vrij, J. Colloid ; Interface Sci. 128 (1989) 121-13689