Ultrafast to Slow Liquid Crystal Dynamics: Experiments and Theory

1. Ultrafast to Slow Liquid Crystal Dynamics: Experiments and Theory Michael D. Fayer, Stanford University,DMR-0088942 The dynamics of six nematogens in the isotropic phaseand three nematic phase liquid crystals were studied with optical heterodyne detected optical Kerr effectexperiments from hundreds of femtoseconds to microseconds. These are the first detailed experimentscovering the full range of times scales in the isotropic phase. The data (upper panel) show two power lawsand a final exponential decay. Only the exponentialdecay has been studied previously and explained withthe Landau-de Gennes theory. A mode coupling theory was developed that reproduces the entire timerange (red dashed curve through data). The lowerpanel shows the first experiments to examine the orientational dynamics of liquid crystals in the nematic phase from very fast times to long times. Note the very different functional form of the dynamics in the isotropic and nematic phases. Dynamics of liquid crystals are being compared to supercooled liquids, and recently experiments have begun on discotic liquid crystals. Over 6 decades in time and over 3 decades in amplitude. J. Chem. Phys. 124, 014902(8) (2006) J. Chem. Phys. 124, 044906(7) (2006)

2. Ultrafast to Slow Liquid Crystal Dynamics: Experiments and Theory Michael D. Fayer, Stanford University,DMR-0088942 Outreach: The PI is participating in an NSF sponsored program to bring high school science teachers into the research laboratory over the summer. Laura Robeck teaches physics and math at Carlmont High, Sequoia Union High School District in Belmont, California. Laura is spending the summer in the Fayer labs. She has become involved in Education: Three graduate students (Hu Cang, Kendall Fruchey, and Ji Li) contributed to this work. All three of these students are exceedingly talented. They have developed skills in complex experimental system design and implementation, and computer programming for control of experiments and for mathematical modeling of physical phenomena. Of most importance, they learn to combine skills to attack scientific problems. Hu Cang has recently begun a post doc at the University of California at Berkeley in the area of biophysics. Jie Li just began a job with Nanometrics, a company that specializes in analytical spectroscopic instrumentation for the semiconductor industry. Kendall Fruchey is continuing his graduate studies in the Fayer labs at Stanford. all aspects of the research program. Laura is preparing samples, using, ultrafast IR lasers, and computer analysis of data in her research on nanoscopic water in molecular environments.