ELECTRICALLY-INDUCED FLOWS IN FERROELECTRIC LIQUID-CRYSTAL FILMS

We review six different physical mechanisms that lead to alternating e lectric field induced flows in ferroelectric liquid crystals. Linear e lectromechanical effects are mainly caused by director rotation induce d flows and by electroclinic induced variation of the layer spacing. T ransient vibrations occur at fast field reversal due to ''inverse elec troclinic'' which attracts the plates before the collective director r otation is activated. During full rotation of the director around a co ne the pressure varies yielding vertical vibrations with higher harmon ic components. Periodic fields also induce ''pumping'' effects. A pump ing can be caused either by a flow parallel to the plates, or by an in crease of the sample thickness. The unidirectional flow reflects the c hirality of the system, whereas the increase of the sample thickness c annot be connected to the chirality.