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Spatiotemporal chaos in electroconvection of a homeotropically aligned nematic liquid crystal Sheng-Qi Zhou and Guenter Ahlers
 

Summary: Spatiotemporal chaos in electroconvection of a homeotropically aligned nematic liquid crystal
Sheng-Qi Zhou and Guenter Ahlers
Department of Physics and iQCD, University of California, Santa Barbara, California 93106, USA
Received 27 April 2006; published 19 October 2006
We present patterns of electroconvection EC for the homeotropically aligned nematic liquid crystal
MBBA. A voltage V= 2V0 sin 2 ft was applied. With increasing V0, the bend Freedericksz transition at VF
was followed by the onset of EC at Vc VF. We found four distinct pattern types. First, a primary supercritical
Hopf bifurcation to traveling waves TW's of convection rolls occurred. The structure factor S k of this state
reflected the azimuthal anisotropy of the underlying Freedericksz state. For f fL 75 Hz there was a super-
position of two oblique-roll modes pattern I . These patterns were chaotic in space and time. For larger f the
patterns consisted of chaotic TW normal rolls pattern II . Here the chaos was attributable to the motion of
dislocations and domain walls between left- and right-traveling waves. A secondary bifurcation yielded pattern
III; it had no dominant TW frequency but had broadband chaotic dynamics dominated by the motion of
dislocations. This pattern type had been referred to by others as a "chevron pattern;" its structure factor still
revealed azimuthal anisotropy. Finally, at somewhat larger V2
/Vc
2
-1 a highly disordered pattern IV with
defect dynamics was found. This state had been studied before by Kai and co-workers and was referred to by
them as "phase turbulence." It had a structure factor that was within our resolution invariant under rotation.

  

Source: Ahlers, Guenter - Department of Physics, University of California at Santa Barbara

 

Collections: Physics