6533b854fe1ef96bd12ae8ea

RESEARCH PRODUCT

Optical tweezing electrophoresis of isolated, highly charged colloidal spheres

subject

description

Abstract We report on a novel optical tweezing experiment measuring the electrophoretic mobility μ of highly charged spherical particles suspended in water at volume fractions Φ≤2×10 −7 . At deionised conditions μ =2.5×10 −8 m 2 V −1 s −1 , it decreases further upon increasing the salt concentration c . We compare our data to measurements at larger Φ, where generally much larger μ and a qualitatively different dependence on the salt concentration are observed. To characterise the dependence on Φ we performed measurements at no added salt. There the mobility increases in the unordered state but stays constant at μ =6.8×10 −8 m 2 V −1 s −1 as the system develops fluid order. In the ordered regime the salt concentration dependence becomes very pronounced for c ≤10 −5 M. None of the presently observed trends can be understood in terms of the standard electrokinetic model.