Dynamics of simple and ordered liquids

The ultra fast dynamics of a simple and a complex liquid system have been explored through the use of a sub-picosecond Transient grating Optical Kerr effect experiment. These experiments provide access to information on the reorientational dynamics of the systems. The simple liquid is compared to a complex liquid that possesses some extended orientational order. The complex liquid is a liquid crystal in the isotropic phase.;The simple liquid system investigated consists of neat biphenyl and biphenyl in n-heptane solutions. An ultrafast component (100 femtoseconds) associated with librational damping/dephasing is observed. In addition two reorientational components are observed. These are associated with a slow tumbling motion around the short axes of the molecules and the faster internal rotation around the central C-C bond and/or spinning of the whole molecule around the long axis.;The complex liquid is the liquid crystal methoxy benzylidene butyl aniline(MBBA) in the isotropic phase. Liquid crystals maintain some orientational order in the pretransitional region just above the clearing temperature. Measurements of orientational relaxation over 6 decades in time (femtoseconds to nanoseconds) and 10 decades of amplitude are reported for the liquid crystal methoxy benzylidene butyl aniline (MBBA). The measurements were made using the Transient Grating Optical Kerr Effect method. The faster dynamics (picoseconds to nanoseconds) display a power law decay that is temperature independent up to 43...