Measurement of orientational order and mobility of a nematic liquid crystal in random nanometer confinement

Confinement of a nematogen in submicrometer cavities can produce substantial effects on the nematic-isotropic phase transition and on order and orientation of the nematic phase. We combine the methods of C13- and H-NMR1 and broadband dielectric spectroscopy to probe liquid crystalline order and molecular mobility. We find that the dynamics of mesogenic molecules (5CB) in the free volume of nanoporous sol-gel glass (5 nm pore diameter) is as fast as in the free bulk phase. In addition, a boundary layer of molecules with reduced mobility covers the pore walls. Isotropic-nematic transition as well as crystallization of the confined nematogen are considerably suppressed. In order to extract the temperature dependence of the nematic order parameter from NMR data, a mathematical model is applied which describes the combined influences of orientational order and diffusional averaging in randomly oriented pores on NMR spectra of the nematogens.