Simple and direct measurements of pretilt angles in hybrid-aligned nematic liquid-crystal cells

Abstract

We have developed a general approach to perform direct measurements of the pretilt angles from 0° to 75° in hybrid-aligned nematic (HAN) liquid-crystal cells whose cell gaps can also be accurately determined with the help of known pretilt angles. In this paper, we have used a Zeeman laser system to measure the angular-dependence phase retardation of the HAN cells and MATLAB mathematical software to carry out theoretical calculations and fit the measured data to derive the pretilt angles. In general, pretilt angles adjacent to opposite substrates of a HAN cell are different. Our measured pretilt angles of the HAN cell were in good agreement with the measured pretilt angles of two accompanying homogenous cells whose alignment methods were the same as applied to opposite substrates of the HAN cell, respectively. The advantage of direct measurement is easily applicable to measure the pretilt angles of aged HAN cells.

Nematic Structures under Conical Anchoring at Various Director Tilt Angles Specified by Polymethacrylate Compositions

“…The director tilt angles on substrates were found by matching the experimental transmittance curve and theoretical dependence obtained from the phase delay calculated in the approximation of linear variation of the director tilt over the layer thickness. The phase delay is calculated as [ 46 ]: where and are the tilt director angles at the substrates, d is LC layer thickness, is the light incidence angle, . and are the refractive indices for light at the wavelength nm polarized parallel and perpendicular to the director, correspondingly.…”

Electrically Induced Structural Transformations of a Chiral Nematic under Tangential-Conical Boundary Conditions

“…The director tilt angles set with polymethacrylate mixtures were determined by the light transmittance dependence of nematic LC cells on the incidence angle [19,30]. Such dependence was recorded with the optical setup consisting of a He-Ne laser (λ = 632.8 nm), polarizer, rotating platform with LC cell, analyzer and photo-detector.…”