Surface Azimuthal Anchoring Energy between the Grating Surface and Nematic Liquid Crystal Layer Studied by Finite Element Method

Abstract

It has been pointed out that Berreman's topological alignment model is applicable to a fairly shallow grating surface, but not for gratings with deep groove profiles. The reason for Berreman's model breakdown was presumed to be the absence of a second derivative in the algebra of elastic theory. In this paper, the saturation tendency of surface azimuthal anchoring energy as a function of the grating height as decribed by numerical simulation on the basis of finite element method (FEM). A good agreement between FEM and experimental results was also demonstrated.

Surface Azimuthal Anchoring Energy Between the Grating Surface and Nematic Liquid Crystal Layer Studied by Using a Geometric Model

“…For each value of the grating pitch, W φ /k m increases almost linearly with increasing H 2 . In other words, the results are consistent with those obtained by FEM simulations in [13,14], and hence the basic validity of the proposed model is confirmed.…”

“…To satisfy this requirement, the present study proposes a simple geometric model for predicting the azimuthal anchoring energy of nematic liquid crystals on a sinusoidal relief grating surface as a function of the grating height and the grating pitch. It is shown that the results obtained using the proposed model are in good agreement not only with the experimental data [13], but also with those obtained from the Berreman's model and finite element method (FEM) simulations [13,14], respectively. In addition, it is shown that the surface azimuthal anchoring energy of the nematic liquid crystal considered in the present study (4-n-pentyl-4'-cyanobiphenyl (5CB) [15] with the chemical formula C 18 H 19 N) increases as the grating height increases and the grating pitch reduces.…”

“…For comparison purposes, the azimuthal anchoring energy was also evaluated using the Berreman's model and FEM simulations, respectively. According to Berreman's model [11,13,14], the azimuthal anchoring energy can be estimated as…”

28.3: Novel Grating Alignment of LCs for Multi‐Domain Structures

“…In particular, the anchoring energy of the novel grating alignment has exceeded to more than 10 -4 J/m 2 , whereas the conventional grating alignment does not reach 10 -4 J/m 2 . As indicated in the previous paper [12], it is difficult for the conventional grating alignment that exceeds the anchoring energy by more than 10 -4 J/m 2 when a photolithography process in a mass production must be utilized. However, our technology have succeeded to go beyond the past limit and demonstrated the significance for practical uses.…”

“…According to this model, the director of LC molecules aligns along with a groove to minimize the free energy associated with elastic deformation of LC molecules. However, the major drawback in the conventional grating alignment is the difficulty in obtaining higher anchoring energy, even if the groove had a fine pitch with higher aspect ratio [12]. Thus, the conventional method is insufficient for the reliability required for LC devices due to the weak anchoring energy.…”