Understanding of Induced Liquid Crystal Alignment by A Rubbed Polymer Surface

1. Z=z X g x H2 Understanding of Induced Liquid Crystal Alignment by A Rubbed Polymer Surface Y. Ron Shen, Univ. California, BerkeleyDMR-0341688 Polyvinyl cinnamate (PVCi) is an important polymer for electronic industry. Rubbed or uv-irradiated PVCi surface can induce alignment of molecules or liquid crystal films. Surface-specific sum-frequency vibrational spectroscopy allows microscopic study of surface modification by rubbing or irradiation. Soft rubbing: Align protruded Ci planes || to surface normal and  to rubbing  Align LC  to rubbing Hard fubbing: Align both main chains and protruding Ci planes || to rubbing  Align LC  to rubbing

2. Understanding of Induced Liquid Crystal Alignment by A Rubbed Polymer Surface Y. Ron Shen, Univ. California, BerkeleyDMR-0341688 • Polyvinyl cinnamate is a well-known photoresist, but has recently been shown to be an effective polymer template for liquid crystal (LC) alignment by either rubbing or uv irradiation. The latter is particular interesting for the LC industry because it could revolutionize the fabrication process of LC displays. However, the mechanisms for the alignment is not yet understood for lack of probes to monitor the surface structural changes induced by rubbing or irradiation. We apply the surface-specific sum-frequency spectroscopic technique developed in our lab to the study of this problem. Our first measurements on rubbed PVCi focus on the spectral changes of the breathing mode of the cinnamate(Ci) rings on the side chains induced by rubbing. From the intensity variation of the mode with respect to rubbing and beam geometry, the orientation of the cinnamate rings can be readily deduced. The Ci rings in turn align the LC molecules deposited on the rubbed PVCi via phenyl ring interactions between Ci and LC molecules. The spectral results presented here show that softly rubbed PVCi induces LC alignment perpendicular to the rubbing direction, and strongly rubbed PVCi induces LC alignment parallel to rubbing.

3. Outreach/Education Y. Ron Shen, Univ. California, BerkeleyDMR-0341688 Participants in this project experience interdisciplinary research training in modern spectroscopy and soft condensed matter physics preparing them for diverse careers. Thai Truong, a recent PhD student on the project, has accepted a postdoctoral position at the Bio-Imaging Center of the California Institute of Technology. Na Ji, a student working partly on the project, completed her PhD recently, and has received postdoctoral offers from prestigious bioscience groups at Harvard, Berkeley, and the new Howard Hughes Medical Institute at Janelia Farm, Virginia. An exchange student from Taiwan, Eric Chen, received his PhD and has accepted a staff position with the third largest LC display manufacturer in the world. A visitor from University of Calabria, Italy, Dr. Pasquale Pagliusi, has established a long-term collaboration with our group. A Berkeley undergraduate student, Michael Frei, worked for two semesters in the lab to gain experience on research.