Electroconvection in nematic liquid crystals: comparison between experimental results and the hydrodynamic model

We describe experimental observations illustrating the extraordinary sensitivity of pattern formation in electroconvection in nematic liquid crystals to changes in magnitude and sign of dynamic transport coefficients triggered by weak fluctuations from a lower temperature nematic-smectic A phase transition. These results are compared to predictions of a hydrodynamic model (HM). We find two patterns at onset not predicted by HM: a rectangular pattern of short normal rolls, and, at lower temperatures, localized patterns coexisting with the subcritical state.