Order reconstruction patterns in nematic liquid crystal wells

Abstract

We numerically study structural transitions inside shallow sub-micrometre scale wells with square cross section, filled with nematic liquid crystal material. We model the wells within the Landau-de Gennes theory. We obtain two qualitatively different states: (i) the diagonal state with defects for relatively large wells with lateral dimension greater than a critical threshold and (ii) a new, two-dimensional star-like biaxial order reconstruction pattern called the well order-reconstruction structure (WORS), for wells smaller than the critical threshold. The WORS is defined by an uniaxial cross connecting the four vertices of the square cross section. We numerically compute the critical threshold in terms of the bare biaxial correlation length and study its dependence on the temperature and on the anchoring strength on the lateral well surfaces.

Unusual photoanisotropic alignment in amorphous azobenzene polymers

“…Uniaxial hedgehog arrangement has been previously observed in the case of liquid crystals in capillaries. 5 As a similar phenomenon has been observed in bacteriorhodopsin, the question that naturally arises is whether this is common to other molecules with photoinduced trans-cis isomerization cycles? As human vision depends on trans-cis isomerizations of the retinal in the eye, it may be possible that polarized light vision at the peak wavelength of eye sensitivity at 570 nm may depend on a different arrangement of the chromophores than is commonly believed.…”

“…The trans–cis isomerization cycles must proceed through other ways than the proposed inversion and rotation cycles. Uniaxial hedgehog arrangement has been previously observed in the case of liquid crystals in capillaries …”

The Well Order Reconstruction Solution for three-dimensional wells, in the Landau–de Gennes theory

“…Further, we numerically study the effect of surface anchoring on the lateral surfaces on the stability of the WORS, in contrast to the analysis which is restricted to Dirichlet conditions on the lateral surfaces. The WORS ceases to exist as we weaken the tangential boundary conditions on the lateral surfaces; this is expected from [10] since the tangent conditions naturally induce the symmetry of the WORS in severe confinement. Our numerical results yield quantitative estimates for the existence of the WORS as a function of the anchoring strength on the lateral surfaces and these estimates can be of value in further work.…”

Liquid Crystals as Phase Change Materials for Thermal Stabilization

“…Next, we expressed the free energy density as a sum of the condensation nematic term , elastic term , external field term , and surface term [12,13]:…”

“…Our main goal was to identify different mechanisms to control and manipulate the phase change temperature. In general, the presence of nanoparticles (NPs), external electric fields, and other perturbations gives rise to elastic distortions [12][13][14][15][16] that can result in the temperature shift of the phase transition.…”