Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions

Abstract

Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch.

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

“…Apparently, the effect is due to the quite weak polar energy of conical anchoring W 0 ∼ 10 −6 J/m 2 . As a result, both the value of N 0 and the size of the droplet should affect the formed structure similar to the case of CLC in the flat layer with tangential-conical boundary conditions, where the orientational structure depends not only on the ratio of layer thickness to the intrinsic helix pitch but also the CLC layer thickness [52]. The composite material under study can be interesting for the development of CLC dispersed systems in which the layer structure uniformity is an important factor, for instance, for optical lasing [53].…”

“…The nematic mixture LN-396 (Belarusian State Technological University, Minsk, Belarus) doped with the left-handed chiral additive cholesteryl acetate (Sigma Aldrich, St. Louis, MO, USA) was used as a cholesteric. The concentration of cholesteryl acetate was 1.5%, that corresponds to p 0 = 9.7 µm [52]. The cholesteric was dispersed in thermoplastic poly(isobutyl methacrylate) (PiBMA) (Sigma Aldrich, St. Louis, MO, USA) having the glass transition temperature T g = 65 • C. The samples were made by solvent-induced phase separation technique [1].…”

Electrically induced transformations of defects in cholesteric layer with tangential-conical boundary conditions

“…Recently, we have studied the cholesteric structures with tangential-conical boundary conditions ( Fig. 1), in which the conical anchoring at one of the substrates was specified by the polymer film 38 . In this case, the twisted defect-free structure or the structure with defect walls is formed in the cell at the values of d/p less than 0.28 (d ≅ 6.5 μm).…”

“…At d∕p ≥ 0.60 the periodic structure with the period approximately equal to the double helix pitch is formed. The twisted structure with the of d/p has a twisted structure with the virtual defects which look like the elongated loops or the pairs of lines whose ends are located at the lateral edges of the LC layer when the sample is observed using a polarising microscope 38 . The optical textures of CLC layer with d = 22 μm and d/p = 0.57 are presented in Fig.…”

“…The director orientation far from defect loop was calculated by free energy minimisation procedure. Near the defect loop the values of the polar and azimuthal angles of the director were analytically extrapolated based on the experimentally measured values of ϕ d (h), where h is a distance from the centre of the defect line 38 . For obtained orientational structures the dependences of the extinction bands position observed in polarised white light on the β angle (angle between rubbing direction R and analyser) were calculated ( Fig.…”