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.
Vilfan
M
M
J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia. mika.vilfan@ijs.si
Apih
T
T
Gregorovic
A
A
Zalar
B
B
Lahajnar
G
G
Zumer
S
S
Hinze
G
G
Böhmer
R
R
Althoff
G
G
D004058:Diffusion; D005898:Glass / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011108:Polymers / Q000737:chemistry*; D016062:Porosity; D012212:Rheology; D013696:Temperature
D011108:Polymers; C422409:liquid crystal polymer