Factors affecting the phase separation of liquid crystals from acrylate-based polymer matrices.

摘要

This dissertation studies the impact of three fundamental factors that affect the phase separation of liquid crystals in polymer dispersed liquid crystals. The first part of this study involves the determination of the effect of increasing polymer molecular weight on the solubility of the LC 4'-octyl-4-biphenyl carbonitrile, or 8CB, in poly(methyl methacrylate), or PMMA. Phase diagrams show what appears to be an upper limit to the effect of polymer molecular weight, a result quantified by extraction of the Flory-Huggins interaction parameter from fits of the microscopy data to the Flory-Huggins theory for polymer solutions. The solubility limit data also show a limit to the effect of polymer molecular weight, and when compared to solubility limit data from previous studies that use different polymer matrices, the data supports the independence of the solubility limit from polymer composition. The second part of this work changes the emphasis of the study from the effect of polymer molecular weight to fluorination of the polymer matrix. Monomers of 2,2,2-trifluoro ethyl methacrylate, TFEMA, and methyl methacrylate, MMA, are polymerized by atom transfer radical polymerization, or ATRP, to form copolymers with 8, 19, 25, 44, and 70% TFEMA content. As the TFEMA content of the copolymer increases, a corresponding increase in the region of immiscibility of 8CB is observed. In order to quantify the effect of increasing TFEMA content, the Flory-Huggins interaction parameters for each blend are determined from the fitting procedure used in the previous section. The final part of this thesis employs time-resolved light scattering to study the phase separation kinetics of the LC blend E7 from a polymer matrix formed by polymerization-induced phase separation, or PIPS. The light scattering experiments start with syrups that consist of two different E7 fractions, 40 and 50% by mass. The scattering profiles for the lowest cure beam intensity exhibit behavior that supports phase separation by a spinodal decomposition mechanism. Higher cure beam intensities exhibit complex growth of the LC domains due to competition between the rapid quenching of the blends and cross-linking of the polymer matrix.