Controlling the alignment of liquid crystals by nanoparticle-doped and UV-treated polyimide alignment films

Role of Surface Hydrophobicity in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment Systems

“…13,14,17 It has been found that the monomers tend to locate around the cell surface, 20 where polymer films were also found. 18,19 However, control of the pretilt angle of LCs has also been investigated by modifying chemical properties of the alignment layer surfaces, for example, the introduction of long linear alkyl side chains or other nonpolar groups to the polymer alignment layers, 21,22 the mechanical rubbing of polymers by varying rubbing conditions, 1,2,8,23 the alignment layer treatments with UV exposure or O 2 plasma, 7,21 and doping 24,25 or composition adjustment 26,27 in the alignment layer. All of these studies demonstrated a consistent tendency between the pretilt angle and the surface energy of the alignment layer.…”

Role of Monomer Alkyl Chain Length in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment System

“…According to the semiempirical Friedel–Creagh–Kmetz (FCK) rule, LC molecules exhibit homeotropic alignment on low energy surfaces and homogeneous alignment on high energy surfaces. Many studies have confirmed that the pretilt angle shifts along with surface hydrophobicity based on this rule. ,,,, These two theories do not necessarily conflict with each other; however, the first one only describes possible behavior during polymerization reaction, yet the other one can also well describe the pretilt angle controlled by other methods.…”

“…Many studies have confirmed that the pretilt angle shifts along with surface hydrophobicity based on this rule. 11,14,20,26,27 These two theories do not necessarily conflict with each other; however, the first one only describes possible behavior during polymerization reaction, yet the other one can also well describe the pretilt angle controlled by other methods.…”

“…In general, pretilt angle results from the interaction between LC molecules and alignment film surface, which is subject to surface chemical properties, molecular structure of LC, surface morphology, and so on. There are several methods that have been developed for tuning LC pretilt angle in the cell, including using polymer alignment layer with long alkyl side chains or nonpolar groups, − tuning rubbing conditions, , application of surface modification, − or utilization of composite and new material alignment film. − Among numerous techniques, polymer-stabilized LC is one of the most promising methods. − To control the pretilt angle, monomers are doped into the LC solution. Polymerization is triggered while LC molecules are subjected to electric field, which guides the molecules into uniform alignment.…”