Liquid Crystal Influenced Self-assembly in Mesogenic Polymer and Liquid Crystal Blends
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Liquid Crystal Influenced Self-assembly in Mesogenic Polymer and Liquid Crystal Blends Lanfang Li, Carmen Otilia Catanescu, Liang-Chy Chien Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio ABSTRACT In this work, we found that by performing photo-polymerization of the mesogenic monomer RM257 in liquid crystals, well organized polymer walls were formed through out the cell by self-assembly of the polymer within the anisotropic host – the liquid crystal. The polymerization conditions, which were parameterized as UV intensity, photo-reactivity (characterized by photo initiator concentration), curing temperature, monomer concentration and mesophase of the liquid crystal host, were systematically varied. Different liquid crystal host also raised some difference in polymer network. We believe this kind of morphology comes from spinodal decomposition and the anisotropic elastic property of the liquid crystal host. It is found that for RM257 and low molecular weight nematic liquid crystals a monomer concentration of 5% is sufficient to use liquid crystal hosts to work as templates for well structured polymer walls. Keywords: phase separation, polymer liquid crystal composite, morphology, photo-induced polymerization INTRODUCTION Ever since J. W. Doane and his coworkers studied liquid crystals (LC) and polymer composites[1], a lot of work has been done in this area, and most attention was put into the use of this kind of materials for electro-optical devices. The morphology of polymers formed this way were also intensively studied [2,3], because it was reported that the morphology of the polymer will affect the electro-optical performance of polymer-liquid crystal composites, commonly described as Polymer Dispersed Liquid Crystals (PDLC), and Polymer Stabilized Liquid Crystals (PSLC) . Mesogenic monomer in liquid crystal host has also been studied [4,5]. Mostly often reported polymer morphologies were droplets or interconnected networks [6,7], while in this work, we found that well organized polymer walls were formed through out the whole sample (in the shape of a thin film). It is understood that polymer morphology largely results from phase separation during polymerization, and it was reported that many parameters, such as types of matrix and LC, and concentrations of the components, influence the phase-separation process [8]. Thus, to understand why we obtained those well organized polymer walls the relationship between polymer morphology and photo-polymerization conditions were investigated by carefully controlling parameters such as UV intensity, concentration of components, curing temperature and the mesophase of the liquid crystal host. EXPERIMENTAL Sample preparation Mesogenic diacrylate monomer RM257 was completely dissolved in liquid crystals 8CB, BDH 13739, TL213, E31, BL006, and MLC6815, respectively, by ultrasonification in
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dichlomethane followed by vacuum evaporation of the solvent for 2 days. Photoinitiator IRG 651, which works with long wavelength UV irradiati
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