Abstract
Dependence of the director tilt angle of nematic liquid crystal (LC) under conical anchoring from the two-component polymer mixture composition has been studied. We varied the ratio of poly(isobutyl methacrylate) (PiBMA), which specifies a conical anchoring for the nematic liquid crystal LN-396, and poly(methylmethacrylate) (PMMA) assigning a tangential alignment for the same nematic. An oblique incidence light technique to determine a tilt angle has been used. It has been shown that the tilt angle increases from to when PiBMA:PMMA ratio changes in the range 30:70 to 100:0. The specific optical textures viewed under the polarizing microscope and proper orientational structures have been considered for various compositions of the polymer films. An electric field action on the formed orientational structures has been investigated. The obtained results are promising for the application in various electro-optical LC devices with a conical anchoring in which the director tilt angle is a crucial parameter: a controlled diffraction gratings, an electrically operated achromatic rotators of linear light polarization, etc.
Highlights
Liquid crystals (LC) have the long-range order of molecules that determines the anisotropy of their properties [1]
We study the dependence of the director tilt angle, the formed orientational structures of nematic, and their response to an electric field from the polymers mixture composition
Three LC cell types have been studied: (i) both substrates were covered with the rubbed films of poly(isobutyl methacrylate) (PiBMA):PMMA mixture; (ii) one substrate was covered with the rubbed Polyvinyl alcohol (PVA) film and the other was covered with the unrubbed film of PiBMA:PMMA mixture; (iii) one substrate was covered with the rubbed PVA film and the other was covered with the unrubbed film of PiBMA:PMMA mixture doped with 20% LN-396
Summary
Liquid crystals (LC) have the long-range order of molecules that determines the anisotropy of their properties [1]. Electric, magnetic, and other LC characteristics depend on the director field distribution n (the unit vector directed along the preferred orientation of LC molecules), which, in turn, is determined by boundary conditions, material LC parameters, and a cell size [2] Boundary conditions assign both an initial LC orientation and its response to the external influences [3]. LC structures under tangential (θ0 angle between the director and substrate plane is 0◦) (Figure 1a) or homeotropic (θ0 ∼= 90◦) (Figure 1b) boundary conditions are widely applied in the displays, electrically controlled wave plates, polarization rotators, phase spatial light modulators, and et al It should be noted that usually the boundary conditions with strictly θ0 = 0◦ or θ0 = 90◦ angle are not used in such devices, and the director has a pre-tilt angle (about a few degrees). In most cases, when assigning the director tilt angle, the homogeneous azimuthal orientation is formed due to the rubbing of both LC cell substrates
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