RANDOMLY CONSTRAINED ORIENTATIONAL ORDER IN POROUS-GLASS

Magnetic resonance and calorimetric studies of 4'-n-pentyl-4-cyanobiphenyl confined to Vycor glass, a random network of pores with average diameter approximately 70 angstrom, are reported. Under such severely constrained conditions, the nematic-to-isotropic transition is replaced by a continuous evolution of orientational order in the pores. Our findings are explained by a Landau type of model where the liquid crystal is confined to independent pore segments, suggesting that the glassylike orientational order is to a large extent locally determined.