PARANEMATIC-NEMATIC PHASE-TRANSITION OF A LIQUID-CRYSTAL CONFINED TO A CONTROLLED POROUS-GLASS

A deuteron NMR study of a pentylcyanobiphenil (5CB) liquid crystal con fined in controlled pore glass (CPG) matrices of different pore diamet ers 2R between 7 nm and 400 nm has been performed. The paranematic-nem atic (P-N) phase transition seems to be gradual in pores with 2R less than or equal to 24 nm and discontinuous in larger pores. Possible rea sons for the observed temperature shift Delta T and qualitative change of the phase transition are analyzed using a simple phenomenological approach. The theoretical analysis suggests that both surface interact ion and elastic distortions significantly influence the Delta T = Delt a T(R) dependence obtained in CPG samples.