Isotropic-Smectic A transition in Liquid-Crystal-Aerosil Dispersions We investigated quenched disorder effects on 12CB liquid crystal upon dispersion of silica nano particles. The LC-aerosil dispersions form a gel if aerosil density exceeds the gelation threshold [1, 2]. On the onset of LC phase, the field anneals a random disorder introduced by aerosil up to a certain density beyond which, disordering effects dominate and there is no longer any influence from the external magnetic field. Even small amounts of aerosil lock in the LC configuration which exhibits a P2 (CosÈ) dependence upon dispersion rotation in the field. The aerosil induced static disorder, is linearly related to the silica density. DNMR Studies of Orientational Order of Banana Shaped Liquid Crystal We examined the thermotropic behavior of banana shaped liquid crystal VPA 103 in the bulk phase and under a cylindrical confinement provided by anodized alumina membranes having 200nm diameters pores. We determined the molecular arrangement of the banana molecules and thermotropic behavior of the bulk phase, as well as of the banana LC molecules under confinement. We also studied the spin-spin relaxation rates in several phases as a function of decreasing temperature, beginning from the isotropic phase. In the bulk system, there is an unusual powder pattern is suggestive of the Nb phase. The biaxiality order parameter is of the order of 0.11 and increased molecular biaxiality of VPA 103 might be responsible for the phase biaxiality. We will also discuss the possible impact of dipole moment on the phase biaxiality. Apart from pre-transitional motion prior to the onset of uniaxial nematic (Nu) phase while cooling, OO increases by about 200% as compared to the order parameter observed at the first appearance of Nu phase at I-Nu transition, while decreasing the temperature from isotropic phase. We will also discuss the studies of mixtures of uniaxial and biaxial molecules. References:  Tao Jin and Daniele Finotello Phys Rev E 69, 041704 (2004)  Germano S. Iannacchione, Sungil Park, Carl W. Garland, Robert J. Birgeneau and Robert L. Leheny Phys. Rev. E 67,011709 (2003)
|School:||Kent State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/08(E), Dissertation Abstracts International|
|Keywords:||Aerosil, Nmr, Vpa103|
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