title: Mapping molecular conformation and orientation of polyimide surfaces for homeotropic liquid crystal alignment by nonlinear optical spectroscopy.
abstract: Surface-specific sum-frequency vibrational spectroscopy and second-harmonic generation were used to study the structures of polyimide (PI) surfaces for homeotropic liquid crystal (LC) alignment and the molecular orientation of LC adsobates on these surfaces. The imide ring was perpendicular to the surface with one of CO bonds protruding out of the surface and the other pointing into the bulk rather than flat on the surface. The ester CO bond in the side chain was sticking out of the surface with a tilt angle of about 45 degrees -55 degrees from the surface normal, indicating that the rigid side chain core was, more or less, along the surface normal. The part of alkyl chain on the top of the side chain followed the orientation of the side chain core and protruded out of the surface with some gauche defects. The cyano biphenyl LC molecules were adsorbed on the PI preferentially with the terminal cyano group facing the PI surface.
authors.affiliation: Yokoyama Nano-structured LC Project, ERATO, Japan Science & Technology Agency, 5-9-9 Tokodai, Tsukuba,Ibaraki-ken 300-2635, Japan. oh-e@nanolc.jst.go.jp
authors.forename: Masahito
authors.initials: M
authors.lastname: Oh-E
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yokoyama
authors.forename: Doseok
authors.initials: D
authors.lastname: Kim
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D007094:Imides / Q000737:chemistry*; D015233:Models, Statistical; D008962:Models, Theoretical; D008968:Molecular Conformation; D011108:Polymers; D013696:Temperature
chemical_list: D007094:Imides; D011108:Polymers; C422409:liquid crystal polymer