Patterns of electroconvection in the nematic liquid crystal N4

Electroconvection using the liquid crystal N4 is studied as a function of two control parameters: the applied frequency and the applied voltage. As a function of voltage, there is a rich series of bifurcations that takes the system from stationary rolls to chaos. As a function of the frequency, the initial pattern changes from stationary oblique rolls at low frequencies to stationary normal rolls at higher frequencies. There is also a change in the secondary bifurcations. In particular, we observe that the bimodal-varicose instability is replaced by the skewed-varicose instability as the applied frequency is increased. Comparisons with theoretical predictions are made.