Measurements of the electrokinetic forces on dielectric microparticles in nematic liquid crystals using optical trapping

Abstract

We have studied the dynamics of dielectric microparticles dispersed in a nematic liquid crystal (NLC) in the presence of an external AC electric field. Investigations were performed using optical trapping technique in the cell with in-plane electrodes. It was shown that the main driving force in the bulk of the material has electrophoretic nature. It was demonstrated that the microparticle behavior strongly depends on the distance with respect to the electrode and is influenced by the dielectrophoretic force. The model, which enables estimation of the electrokinetic forces, is proposed. The forces are found from the balance with the optical trapping force. The microparticle surface charge q≈2.1×10−17 C, linear electrophoretic mobilities μ∥≈10−11 m2/(V⋅s),μ⊥≈7×10−12 m2/(V⋅s), and the NLC viscosity η≈(21.2±4.7)×10−3 Pa⋅s at T=40 °C are evaluated.