Abstract
Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.
Highlights
MethodsWe investigated the well-known nematic liquid crystals (LCs) 4-metoxybenzylidene-4'-butylaniline (MBBA) [22]and 4-n-pentyl-4'-cyanobiphenyl (5CB) [23] (both from Merck, Darmstadt, Germany) with the phase transition sequences Cr-22°C-N-47°C-I and Cr-21.5°C-N-35°C-I, respectively
The study of structural ordering of liquid crystals (LCs) is of great importance for both the development of physics of condensed matter and application
We investigated the domain structures occurring in the nematic liquid crystals deposited onto the surface of a polycarbonate film obtained with the use of solvents with different solvations
Summary
We investigated the well-known nematic LCs 4-metoxybenzylidene-4'-butylaniline (MBBA) [22]and 4-n-pentyl-4'-cyanobiphenyl (5CB) [23] (both from Merck, Darmstadt, Germany) with the phase transition sequences Cr-22°C-N-47°C-I and Cr-21.5°C-N-35°C-I, respectively. Rigid chain polymer polycarbonate (PC) was used as an orienting surface. Whose groups are coupled with carbonate groups in a polymer chain. We applied Poly (Bisphenol A carbonate) with average molecular weight M ~45000 from Sigma-Aldrich Co. LLC (St. Louis, MO, USA). Polycarbonate grains were dissolved in the solvents with different solvations in PC: dichloromethane (CH2Cl2), chloroform (CHCl3), or pyridine (C5H5N) in concentration of 2%. We applied the dichloromethane stabilized with ~20 ppm of amylene, chloroform stabilized with ~150 ppm of amylene and pyridine, 99% PS from Panreac Quimica S.L.U (Barcelona, Spain). The polymer solutions were deposited onto a smooth clean glass surface by centrifugation or flowing. At the solvent evaporation for several seconds with average evaporating rate 40%/min, a PC film formed on the glass surface. The film thickness was from 100 nm using centrifugation to few microns when applying the method of flowing. The thickness of film was measured using a device Filmetric F50-UVX
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