LIQUID-CRYSTALLINE BEHAVIOR OF OCTYLCYANOBIPHENYL CONFINED TO SUBMICRON-SIZE RANDOMLY CONNECTED POROUS GLASSES

We report a study of the orientational order via deuterium NMR and hig h resolution sc calorimetry on octylcyanobiphenyl (8CB) confined to ra ndomly oriented and interconnected macroporous (1000 Angstrom mean por e size) and microporous (100 Angstrom mean pore size) glasses. In the macroporous glass, the nematic to isotropic (N-I) phase transition ret ains the bulklike weakly first order nature. The nematic phase is char acterized by an NMR powder pattern spectra, as expected fora director distribution with no preferred spatial direction, and it coexists with an isotropiclike component. The orientational order is slightly suppr essed from the bulk's and there is no sudden increase in orientational order due to the onset of the smectic phase suggesting a weaker coupl ing between nematic and smectic order parameters. Further, due to the confining size, the smectic-A to nematic transition is considerably su ppressed and broadened. In the microporous glass, the orientational or der behavior is reminiscent of that in Vycor glass. No phase transitio ns are detected, rather, there is a continuous evolution of local orie ntational order. Interporous and intraporous interactions are importan t.