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

• Published in: Magnetic resonance imaging 2001-04, Vol.19 (3), p.433-438
• Main Authors: Vilfan, M., Apih, T., G regorovič, A., Zalar, B., Lahajnar, G., Žumer, S., Hinze, G., Böhmer, R., Althoff, G.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Diffusion; Glass - chemistry; Investigative techniques, diagnostic techniques (general aspects); Liquid crystal; Magnetic Resonance Spectroscopy - methods; Medical sciences; Miscellaneous. Technology; NMR; Polymers - chemistry; Porosity; Porous glass; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Rheology; Surface-induced order; Temperature
• ISSN: 0730-725X; 1873-5894
• DOI: 10.1016/S0730-725X(01)00262-4

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 ∼ 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.