Brownian motors in the photoalignment of liquid crystals

In the photoalignment of liquid crystals with dissolved dyes or in the pres ence of dye doped alignment layers, light can cause reorientation of the li quid crystal director against a restoring elastic torque essentially withou t the transfer of angular momentum. We show that this phenomenon originates in an orientational ratchet mechanism, where, under photoexcitation, the d ye molecules act as rotors of a Brownian motor. (C) 2000 Elsevier Science L td. All rights reserved.