In situ laser-imprinted surface realignment of a nematic liquid crystal

Abstract

We present a new method for the in-plane realignment of nematic liquid crystals in already fully assembled cells with uni-directionally rubbed polyimide as an aligning layer. We use nematic liquid crystals (NLCs) with a relatively high nematic-isotropic transition temperature and we focus the IR laser beam of the laser tweezers selectively onto one or the other of the inner interfaces. The heat generated by the IR absorption locally melts the liquid crystal and creates an isotropic island with well-defined molecular anchoring at the nematic-isotropic interface. By scanning the laser beam along a pre-defined line, the moving isotropic-nematic interface leaves behind a well oriented LC domain, with LC molecules aligned at 45° to the rubbing direction. If we in addition move the sample with respect to this scanning line, we would be able to selectively realign micro-domains of the liquid crystal with respect to the original alignment induced by the PI rubbing. The realignment can be performed independently on each LC-glass interface, thereby producing predefined domains with customized and controllable alignment within an otherwise uniformly aligned cell.

Structural, Optical and Dynamic Properties of Thin Smectic Films

“…It should be noted that both these potentials V i and V ij describe the interactions of the ith layer with confining surfaces and the pair interactions between ith and jth molecules, respectively. Here (...) i is the statistical-mechanical average with respect to the one-particle distribution function of the ith layer [7,38]…”

“…where z i is the dimensionless distance through the smectic film, V 0 is the force potentials which is responsible for the molecule-molecule interaction, W 0 is the parameter corresponding to "enhanced" pair interactions in the bounding layers, and the constant α implicitly characterizes molecular packing across smectic layers [38]. Physically, these approaches indicate that we replace V 0 by W 0 within the first and last layers, whereas for all interior layers 1 < i < N the interaction coefficient V 0 has not been changed.…”

“…Taking into account this fact, in the theoretical investigations the initial thickness of the film was chosen as being equal to N = 25 [7,11,12,17,[19][20][21]. According to the McMillan's theory [38], the first-order bulk AI transition occurs for α ≥ 0.98, so, the choosing of α = 1.05 is acceptable. When choosing the value of W 0 /V 0 , one is usually guided by the fact that the partially fluorinated free-standing smectic films composed of the H10F5MOPP molecules are stable above the θ AI (bulk).…”

“…In the number of theoretical investigations [7,11,12,17,[19][20][21] the strong surface-enhanced pair interactions with W 0 = 5 V 0 has been chosen. Taking into account that the partially fluorinated compound H10F5MOPP has bulk SmA-I transition temperature T AI (bulk) ∼ 358 K, (θ AI (bulk) ∼ 0.675) and for α = 1.05, according to the McMillan's theory [38], the value of k B T AI (bulk)/0.2202V 0 = 1.021, one can estimate that the value of V 0 is equal to ∼ 2.2 × 10 −20 J. Please note that values of the dimensionless temperature θ = 3k B T V 0 often vary between 0.60 (∼ 318.2 K) and 0.80 (∼ 424.3 K) [7,11,12,17].…”

Broadband Spectral Domain Interferometry for Optical Characterization of Nematic Liquid Crystals

“…ordinary, axis) and a high nematic-to-isotropic phase transition temperature (T c = 387 K). However, although the mixture is referenced in some publications, little information is available and it originates from the manufacturer [18,19]. To determine the advantage of MLC2132 for the above-mentioned applications, an in-depth characterization of its anisotropic optical properties is needed.…”