Surface-induced order and diffusion in 5CB liquid crystal confined to porous glass. |
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Authors: | M Vilfan T Apih A Gregorovic B Zalar G Lahajnar S Zumer G Hinze R B?hmer G Althoff |
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Institution: | J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia. mika.vilfan@ijs.si |
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Abstract: | Liquid crystals confined into small cavities are known to have a weak orientational order even above the nematic-isotropic transition temperature. The surface-induced order and molecular dynamics in this temperature range are studied with the aid of deuteron NMR spectra, spin relaxation times T(1) and T(2,) proton dipolar-correlation effect, and direct measurements of the effective diffusion coefficient for the liquid crystal 5CB confined to controlled-pore glasses. Our results show that an arrangement of molecules parallel to the wall is induced by local molecular interactions between the liquid crystal and solid, resulting in a weak and temperature independent surface order parameter, S(0) approximately 0.02 +/- 0.01. There is no indication of a significant slowing-down of molecular diffusion at the wall, neither rotational nor translational. In cavities of nanometer size, where the nematic order evolves gradually upon cooling, a broadening of the NMR linewidths due to dynamic effects should be taken into account. |
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