Phase diagrams and morphology of polymer dispersed liquid crystals based on nematic-liquid-crystal-monofunctional-acrylate mixtures

Phase diagrams of unpolymerized and UV-polymerized 2-ethyl hexyl acrylate ( EHA) mixtures with the liquid crystal E7 are established using optical micr oscopy and differential scanning calorimetry. Both diagrams show upper crit ical solution temperature behavior. From 50 to 90 wt % liquid crystal (LC), the (I + I) phase located between the (N + I) and (I) phases was clearly s hown. The nematic phase inside the droplets exhibits a twisted radial struc ture indicating that homeotropic anchoring occurs at the polymer interface. The experimental phase diagrams were successfully analyzed using a model b ased on the Flory-Huggins theory of isotropic mixing supplemented with the Maier-Saupe theory of nematic order. The LC solubility limit in the polymer matrix and the fractional amount of LC contained in the droplets were dedu ced from the calorimetric measurements. For the specific composition EHA/E7 (50:50), the scattering and morphological properties of the films were stu died as a function of time elapsed after UV exposure. Drastic changes in th e size, shape, spatial distribution, and number density of nematic droplets were observed and analyzed in terms of coalescence/diffusion phenomena.