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In Ref. (1), a phenomenological theory of pressure effects of nematic liquid crystals is given and used successfully in the interpretation of a large amount of experimental data. On this basis, in this paper, problems related to the free energy Go(P, T) of the isotropic phase are discussed, experiments of S(V T), P(V, T), In T ∼ In V(S fixed), etc. are explained, predictions including the relations S(V. T), KT(P), etc. are presented. Here, S is the order parameter, KT the isothermal compressibility. Related theories and experiments of pressure effects in the literature are discussed and compared. Results in this paper strengthen further the basic assumptions of the theory given in Ref. (1).

There exists a variety of important new phenomena and plenty of experimental data on the pressure effects of liquid crystals. Yet, no systematic phenomenological or microscopic theory is available. In this paper, the ordinary Landau-deGennes theory is generalized so that the free energy becomes G = Go(P, T) + a/2 [T - T*(P)]S2 - B(P)/3 S3 + C(P)/4 S4, T*(P) = To + bP - eP2. All the known pressure experiments of nematic PAA (where B and C are independent of P) are explained in one stroke and all parameters are determined. New results including reentrant I phase (I represents isotropic phase), and the independence of Tc - T* and T* - Tc on P, etc., are predicted. Simple methods of experimental confirmation are proposed. Similar discussions on the cases of MBBA, EBBA, etc. are also given. Our theory differs from that of Lin-Keyes-Daniels but agrees better with experiments. Results related to GO(P, T) will be reported in a separate paper.