A Gregorovic | PubMed Health

PubMed2000

Interlayer molecular exchange in an anticlinically ordered chiral liquid crystal

The interlayer molecular exchange has been determined in the antiferroelectric smectic-C(*)(A) phase of alphad(2) deuterated 4-(1-methylheptyloxycarbonyl)phenyl4(')-octyloxybiphenyl-4-carboxylat e via quadrupolar deuteron NMR self-diffusion in the spatially varying electric field gradient produced by the anticlinic smectic layer structure. The interlayer self-diffusion coefficient is here by two orders of magnitude smaller than in synclinically ordered smectic phases. The results support the entropic suppression model of the origin of anticlinic smectic ordering. The applied technique could possibly allow for a new insight into the local structure of the intermediate "clock" phases.

Journal Article↗

PubMedDate not supplied

Surface-induced order and diffusion in 5CB liquid crystal confined to porous glass.

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.

Diffusion↗