Dielectrophoresis of Janus particles under high frequency ac-electric fields.

Janus polystyrene particles with gold and dielectric multilayer coatings on one hemisphere are shown to drastically alter the dielectrophoresis (DEP) behavior of homogeneous precursor particles under ac-electric fields. Alkanethiol coatings on the gold-coated hemisphere can effectively modify the DEP crossover frequency (ωc) with a negative (n) to positive (p) (p→n) DEP transition as increasing ac-frequency, in contrast to p→n DEP transition observed with precursor particles. All measured n→p DEP crossover frequencies with dependence on particle size, alkanethiol thickness, and medium conductivity are collapsed to yield a scaling with the resistance-capacitance (RC) time of the alkanethiol layer capacitance and the conductive medium resistance. [ABSTRACT FROM AUTHOR]