Thermal and morphological studies of liquid crystalline materials dispersed in a polymer matrix

Abstract

Polymer dispersed liquid crystal (PDLC) films have been prepared by a combination of solvent-induced phase separation and thermal-induced phase separation techniques, for three mesogenic materials: 4-(undecyloxy) ben-zoic acid (UDBA), 4-(decyloxy) benzoic acid (DBA) and 4-(dodecyloxy) benzoic acid (DDBA) in poly(methyl methacrylate) (PMMA) as polymer matrix and tetrahydrofuran (THF) as common solvent. Differential scanning calorimetry and polarising optical microscopy are used for thermal and morphological investigations of prepared PDLCs, and findings are explained with the help of a suitable phase diagram. It is found that isotropic liquid-ne-matic transition temperature (TIN) for these mesogens in the PMMA matrix decreases by about 2.8-5.6C as compared with the pure mesogens. Methods based on the solubility parameter and the fraction of liquid crystal (LC) in LC-rich domains inside the PMMA matrix at different concentrations have been adopted to achieve an optimised condition for uniform dispersion of the film over a larger area. Remarkable changes in the droplet morphology of the mesogens confined in PMMA matrix as compared with their bulk counterparts have also been observed. Bipolar droplets and Maltese-type crosses are observed by POM for 75 and 30 wt% UDBA in the PMMA matrix. © 2011 Taylor & Francis.