INFLUENCE OF NONMESOGENIC IMPURITIES ON A NEMATIC TO ISOTROPIC-PHASE TRANSITION

Non-mesomorphic solutes depress the normal nematic-isotropic transitio n temperature in liquid crystals. When non-mesomorphic solutes are add ed to a nematic liquid crystal, the nematic-isotropic transition tempe rature is depressed and a two phase region is formed due to the presen ce of impurities of the solutes. The present paper explains the format ion of this two phase region by the Landau-de Gennes phenomenological theory, which agrees fairly well with the experimental observations. W e also note that this two phase region indicates the tricritical behav iour of the nematic-isotropic phase transition and the phase diagram n ear the tricritical point is also obtained.