Phase equilibria and dynamics of thermally-induced and polymerization-induced phase separations in main-chain liquid crystalline polymer mixtures

Dynamics of thermal-induced phase separations and the temporal evolution of the growth of liquid crystalline polymer (LCP) domain size in binary mixtures comprising of a main-chain liquid crystalline polymer (MCLCP) and a flexible polymer have been studied by solving the coupled time dependent Ginzburg-Landau (TDGL, Model C) equations for the conserved compositional order parameter and the non-conserved orientational order parameter. The two coupled TDGL equations have been solved numerically by incorporating the combined Flory-Huggins (FH) theory for isotropic mixing, the Maier-Saupe (MS) theory for nematic ordering and the Flory theory for chain stiffening.; The time evolutions of liquid crystalline polymer domains and structure factors have been simulated on the basis of an explicit central difference method based on a two-dimensional square lattice (128 x 128) with a periodic boundary condition by conducting the temperature quenches into various regions such as liquid-liquid coexistence region, nematic-liquid coexistence region, unstable nematic-liquid region and metastable nematic-liquid region. The time evolution of the scattering patterns has been obtained by taking the two-dimensional fast Fourier transformation (2D FFT) of the compositional domain structures.; The competition of liquid-liquid phase separation and nematic ordering of liquid crystalline polymer has been tested by simulating the T quench experiments into various regions, such as nematic-liquid coexistence region and unstable nematic region. Of particular interest is the observed plateau (or inflection) region in the growth dynamic curve, which may be attributed to the breakdown of the interconnected domains caused by the nematic ordering.; The dynamics of polymerization-induced phase separation (PIPS) and morphology development in an MCLCP/polymer mixture have been investigated by incorporating polycondensation kinetics into the coupled time-dependent Ginzburg Landau (TDGL, Model C) equations. The competition between polymerization kinetics and phase separation has been studied by solving the coupled TDGL equations for both compositional and orientation order parameter. The simulation reveals that both morphological and scattering patterns for the orientational order parameter initially lag behind those of the compositional order parameter. The simulated morphology consists of the LCP droplets dispersed in a matrix of polymer. Of particular interest is the observation of an abrupt change in growth curve associated with the onset of nematic ordering.