Noise-induced Electrohydrodynamic Patterns in Nematic Liquid Crystals

Abstract

We report on noise-induced patterns and threshold characteristics for the ac-driven electrohydrodynamic system in nematic liquid crystals. The wave number-dependence of the threshold for the stochastic system was experimentally investigated with controlling intensity rate of noise. The results are discussed in comparison with the previous experimental and theoretical ones. Moreover, unexpected patterns as well as pre-transitional ones are presented.

Noise Effects on Threshold of Electrohydrodynamic Convection in Nematic Liquid Crystals

“…This means that the deterministic frequency f s (i.e., the wave number k WD ) is an important factor for this behavior of V c . 7,13) This result shows a good qualitative agreement with previous studies 12,21) only for a (low) fixed f s (e.g., 30 Hz in ref. 12).…”

“…5,6) In particular, the present ac-driven electrohydrodynamic system in liquid crystals has been intensively studied from this point of view. [7][8][9][10][11][12][13] In the system, a nematic liquid crystal sandwiched between two electrodes is subjected to an external electric field. If the field is pure deterministic, one finds a rich variety of stationary and nonstationary patterns.…”

“…Up to now, several groups have extensively investigated the threshold shift for the onset of electroconvection by considering the intensity and correlation time of the noise. [7][8][9][10][11][12][13]20) Previous experimental results are as follows: (i) The superposition of the stochastic noise (V N ) increases the deterministic threshold voltage (V c ) for WDs. This means that the noise plays a role in stabilizing the initially stationary state of the system.…”

“…(ii) For a relatively small intensity of the noise, there is a linear relation between V 2 c and V 2 N . [7][8][9][10]13) The slope of the linear relation is affected by the correlation time of the noise ( N ). For certain correlation times comparable to the characteristic time of the system ( 0 ), the slope becomes flat (i.e., no effect of the stochastic noise is induced).…”

“…11,12) (v) Very recently, the wave number dependence of the threshold V c and noise-dominated patterns for the first instability have been reported. 13) In theoretical studies, on the other hand, the observed linear relation was successfully explained, although the physical approaches used were quite different. [7][8][9][10]20) Moreover, the relation was also reported in other systems such as a magnetic (or electric) field-induced Freedericksz transition, which deals with a spatially homogeneous instability in order to avoid the wave number dependence of the noise.…”