Deuteron NMR study of liquid crystals confined in aerogel matrices

The temperature dependence of the deuteron NMR line shape was studied in pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB) liquid crystals confined in porous silica aerogel matrices with two different pore size distributions. The average pore sizes 〈${\mathit{R}}_{\mathit{c}}$〉 of the two aerogel matrices were 0.8 and 0.2 μm, respectively. The deuteron NMR lines of 5CB and 8CB confined liquid crystals are in the isotropic regime broader than in the corresponding bulk phases. This observation shows that the interaction with the aerogel internal surface induces nematic order far above the bulk isotropic-nematic transition temperature. The nematic-isotropic (N-I) transition for both confined liquid crystals is continuous. No hysteresis was observed. A simple Landau-type model is used to describe these observations.