Forma, Vol. 15 (No. 3), pp. 321-328, 2000
Original Paper

Regular Dendritic Patterns in Liquid Crystals Induced by Non-Local Time-Periodic Forcing

Tibor Tóth-Katona, Tamás Börzsönyi, László Gránásy and Ágnes Buka

Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, P.O.B.49, Hungary

(Received April 13, 2000; Accepted May 13, 2000)

Keywords: Pattern Formation, Phase Transitions, Viscous Fingering, Liquid Crystals

Abstract. We explore both experimentally and numerically (by phase-field model) the possibility of controlling the side-branching process by a homogeneous time-periodic forcing on dendrites observed at the nematic-smectic B liquid crystal (LC) interface. We apply either pressure oscillations or a modulated AC voltage. The pressure oscillations generate a periodic change of the phase transition temperature via the Clausius-Clapeyron relation. The modulated electric current causes a temperature oscillation in the sample. We show that both methods can be used for controlling the side-branching process in a range of the relevant parameters. Our experiments performed on viscous fingering demonstrate that dendritic side-branching can be also induced and/or regularized at the nematic—air interface in a radial Hele-Shaw cell by modulated electric field that influences the surface free energy, and the effective viscosity of the nematic LC in the plane of observation.

[Full text] (PDF 932 KB)