Model phase diagrams of binary nematic mixtures. A comparative study between linear and crosslinked polymers

Model calculations of phase diagrams of side chain liquid crystal polymers (SCLCP) and low molecular weight liquid crystals (LMWLC) are presented. The polymer is assumed to have grafted side chain units characterized by a nem atic-isotropic transition temperature T-NI 2, and the LMWLC presents also a similar transition at a temperature T-NI 1. The model calculations can acc ommodate for the cases where the latter two temperatures are comparable or widely different. For the sake of illustration, the case T-NI 1 = 60 degree s C and T-NI 2 = 80 degrees C is adopted here. The main point of interest h ere is to perform a comparative study of the equilibrium phase diagrams of SCLCP made either of linear free chains or crosslinked chains forming a sin gle network. To our knowledge this is the first comparative study of the ph ase behavior of binary nematic mixtures involving linear and crosslinked po lymer matrices which permits to clearly identify the effects of crosslinks present in the polymer matrix. The crosslinks attribute elasticity to the p olymer constituent which induces important distortions in the phase diagram . To highlight these distortions, examples of hypothetical binary nematic m ixtures are chosen involving both Linear and crosslinked polymers with side chain mesogen units. The quadrupole interaction parameter between the two nematogens is related to individual parameters via a geometric average nu(1 2)(2) = kappa nu(11)nu(22) with a coupling parameter kappa. Different value s of this parameter are considered and the impact of coupling strength on t he phase diagram is discussed for crosslinked and linear polymers.