Equilibrium phase behavior of nematic mixtures

Abstract

A phenomenological model for predicting phase diagrams of a binary nematic mixture containing side chain liquid crystalline polymers and/or low molar mass liquid crystals has been proposed by combining Flory–Huggins free energy of isotropic mixing and Maier–Saupe free energy for nematic ordering of the nematogens. Two orientational order parameters, s1 and s2, of the two components in the mixtures having two different clearing temperatures are taken into consideration in the calculation. The Flory–Huggins interaction parameter, χ, and the nematic interaction parameter of the Maier–Saupe theory, ν11 and ν22, are assumed to be functions of inverse absolute temperature. Further the cross-nematic interaction is assumed to be proportional to the square root of the product of the nematic interaction parameters of the two mesogens, i.e., ν12=c (ν11⋅ν22)1/2. The theory predicts a variety of phase diagrams depending on a single parameter, c, which is a measure of a relative strength of interaction between two dissimilar mesogens to that in the same species. The predicted phase diagrams have been tested rigorously with experimental phase diagrams of various nematic mixtures reported by others as well as by us.

Phase separation kinetics in mixtures of flexible polymers and low molecular weight liquid crystals

“…The theoretical results have partly been confirmed by corresponding experimental observations 29,32,33) . One of the key arguments is that there are two spinodal curves in the phase diagram of a PDLC 34,35) , following an important finding by Dorgan 36) in the analysis of SD of an LC solution composed of liquid crystalline polymers and isotropic low molecular weight solvents.…”

“…The anisotropic potential at position i resulting from LC-LC interaction is expressed as 47) , phase behaviors in mixtures containing LCs [27][28][29] , Freedericksz transitions 52) and even the nonlinear rheological behavior of LCs 53) . In our MC simulation, the NI transition temperature is T NI L 310 K for e LL = 270 k (k is the Boltzmann constant).…”

“…During the phase separation process in a rod-coil mixture, the concentration fluctuation associated with a conserved order parameter must be coupled with the orientation fluctuation associated with a nonconserved order parameter, which is essential for a mixture containing mesogenic units, but has not been paid much attention to until recently [37][38][39][40] . All of the preceding theoretical treatments [23][24][25][26][27][28][29][34][35][36][37][38][39][40] were performed applying the mean-field formalism. As emphasized by Binder et al 3,4) , the phase behavior in polymer blends might deviate from the predictions based on the mean-field theory to a large extent.…”

Phase equilibria and phase separation dynamics in a polymer composite containing a main‐chain liquid crystalline polymer

“…[18][19][20] Phase Diagrams of Polymer/Polymer Mixtures That is to say decreasing attractive interaction between the con-stituent molecules or increasing polymer molecular weight, the UCST is moves upward, while the LCST is depressed, forming an immiscibility gap between the UCST and LCST. A similar trend can be expected for a LCP/polymer pair, except that the nematic isotropic transition of the LC constituent is expected to affect the binary phase diagram.…”

“…The nematic spinodal curve is the demarcation line between the nematic metastable and the nematic unstable regions. 17,19,20 As labeled in the phase diagram, the nematic metastable region is bound by the pure nematic and the nematic spinodal line.…”