title: Rubbing-induced anisotropy of long alkyl side chains at polyimide surfaces.
abstract: Molecular organization at polyimide surfaces used as alignment layers in liquid crystal displays was investigated using vibrational sum frequency generation (SFG) spectroscopy. We focus on the orientation of the long alkyl side groups at the polymer surface using polarization-selected SFG spectra of the CH(3)- and CH(2)-stretch modes of the side chain. Mechanical rubbing and baking, an accepted industrial procedure used to produce pretilt of the liquid crystal, was found to induce pronounced azimuthal anisotropy in the orientational distribution of the alkyl side chains. Orientational analysis of the SFG vibrational spectra in terms of the azimuthal and tilt angles (in and out of plane, respectively) of the alkyl side chains shows their preferential tilt along the rubbing direction, with the azimuthal distribution narrower for stronger rubbed polymer samples.
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
authors.forename: Himali D
authors.initials: HD
authors.lastname: Jayathilake
authors.forename: Min Hua
authors.initials: MH
authors.lastname: Zhu
authors.forename: Charles
authors.initials: C
authors.lastname: Rosenblatt
authors.forename: Andrey N
authors.initials: AN
authors.lastname: Bordenyuk
authors.forename: Champika
authors.initials: C
authors.lastname: Weeraman
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Benderskii