Thermodynamics, transition dynamics, and texturing in polymer-dispersed liquid crystals with mesogens exhibiting a direct isotropic/smectic-A transition

摘要

Experimental and modeling/simulation studies of phase equilibrium and growthmorphologies of novel polymer-dispersed liquid crystal (PDLC) mixtures of PS(polystyrene) and liquid crystals that exhibit a direct isotropic/smectic-A(lamellar) mesophase transition were performed for PS/10CB (decyl-cyanobiphenyl) and PS/12CB (dodecyl-cyanobiphenyl). Partial phase diagrams weredetermined using polarized optical microscopy (POM) and differential scanningcalorimetry (DSC) for different compositions of both materials, determiningboth phase separation (liquid/liquid demixing) and phase ordering(isotropic/smectic-A transition) temperatures. The Flory-Huggins theory ofisotropic mixing and Maier-Saupe-McMillan theory for smectic-A liquidcrystalline ordering were used to computationally determine phase diagrams forboth systems, showing good agreement with the experimental results. In additionto thermodynamic observations, growth morphology relations were found dependingon phase transition sequence, quench rate, and material composition. Threestages of liquid crystal-rich domain growth morphology were observed: sphericalmacroscale domain growth ("stage I"), highly anisotropic domain growth ("stageII"), and sub-micron spheroid domain growth ("stage III"). Nano-scale structureof spheroidal and spherocylindrical morphologies were then determined viatwo-dimensional simulation of a high-order Landau-de Gennes model. Morphologiesobserved during stage II growth are typical of di- rect isotropic/smectic-Aphase transitions, such as highly anisotropic "batonnets" and filaments. Thesemorphologies, which are found to be persistent in direct isotropic/smectic-APDLCs, could provide new functionality and applications for these functionalmaterials.