Polarized XANES studies on the rubbed polyimide for liquid crystal alignment; new applicability to the tribology of the polymer systems

Liquid crystal alignment by rubbed polymer surfaces: a microscopic bond orientation model

“…These studies also showed the preferential near-surface alignment of polyimide chain segments along the rubbing direction [17] and the decay of the alignment from the surface toward the bulk of the film. NEXAFS studies also gave clear evidence for a preferential outof-plane tilt of phenyl rings at polyimide surfaces [15,16,18,19]. This tilt was linked with the pretilt angle of the LC on the surface.…”

“…In this model the LC rods are envisioned to align parallel to the polymer chain segments in the crystalline regions. Surface sensitive studies have also been carried out using the near edge X-ray absorption fine structure (NEXAFS) technique [15][16][17][18][19]. These studies also showed the preferential near-surface alignment of polyimide chain segments along the rubbing direction [17] and the decay of the alignment from the surface toward the bulk of the film.…”

Mapping molecular conformation and orientation of polyimide surfaces for homeotropic liquid crystal alignment by nonlinear optical spectroscopy

“…Presently, LC alignment is most commonly achieved by mechanical rubbing of polymercoated substrates [1,2]. The rubbed polyimide (PI) surface aligns an LC monolayer adsorbed on it via short-range interaction, which in turn aligns an LC bulk via LC molecular correlation [3][4][5][6][7][8][9]. This scheme however has some unwanted features in the manufacturing process and alternative methods capable of aligning LC films have been investigated.…”

“…Thus they provide information about surface structure and composition of a polymer. Applications of the techniques to rubbed surfaces of polyvinyl alcohol (PVA) [18] and some PIs [27][28][29] have shown that the surface polymer chains are well aligned along the rubbing direction [12][13][14][15][16][17], and so are the LC molecules adsorbed on them [3][4][5][6][7][8][9]30,31].…”

Dependence of threshold behavior upon surface distribution of polymer chains in a twisted nematic liquid crystal

“…Then the anisotropic distribution of PI chains is responsible for the LC alignment. Surface molecular distribution of PI film treated by rubbing or photoexposure has been revealed through prominent experiments by several scientists [5][6][7][8][9][10][11][12][13]. Despite such experimental results, LC anchoring properties on rubbed surfaces that were considering surface distribution of PI molecules was reported by Baharat R. Acharya et al [14].…”