WEAKLY NONLINEAR-ANALYSIS OF ELECTROCONVECTION IN A SUSPENDED FLUID FILM

It has been experimentally observed that weal;ly conducting suspended films of smectic liquid crystals undergo electroconvection when subjec ted to a large enough potential difference. The resulting counterrotat ing vortices form a very simple connection pattern and exhibit a varie ty of interesting nonlinear effects. The linear stability problem for this system has recently been solved. The convection mechanism, which involves charge separation at the for surfaces of the film, is applica ble to any sufficiently two-dimensional fluid. In this paper, we deriv e an amplitude equation which describes the weakly nonlinear regime, b y starting from the basic electrohydrodynamic equations. This regime h as been the subject of several recent experimental studies. The lowest order amplitude equation we derive is of the Ginzburg-Landau form. an d describes a forward bifurcation. as is observed experimentally. The coefficients of the amplitude equation are calculated and compared wit h the values independently deduced from the linear stability calculati on.