Thermal study of photopolymerization reaction in polyacrylate/liquid crystal blends

International audience ; PDLCs composite materials (Polymer Dispersed Liquid Crystal) were elaborated by polymerization induced phase separation under UV-light. Binary systems composed of Tripropyleneglycol diacrylate (TPGDA) monomer and a liquid crystal mixture (E7) were used as starting materials in the process of polymerization/crosslinking leading to a phase separation between polymer and liquid crystal. The time behaviour of the optical transmission of these films was experimentally studied during the period of exposure to UV-light in the absence of external applied fields. The transmission versus time curves of in-situ UV-cured TPGDA/E7 films reveal three regions: A first domain corresponding to a transparent film of the initial TPGDA/E7 mixture before exposure to UV light, a second time domain where the sample exhibits a fast relaxation process just after the beginning of the UV irradiation of the monomer/LC blend and a unusual third domain, characterised by an enhancement of the film transparency at longer relaxation times. This process depends on the conditions of sample preparation and film thickness. In this study, a temperature of a sample has been controlled after, during and before the application of UV light. ; Des matériaux composites PDLCs (Polymer Dispersed Liquid Crystal) ont été élaborés par séparation de phase induite par polymérisation sous lumière UV. Des systèmes binaires composés de monomère Tripropylèneglycol diacrylate (TPGDA) et d'un mélange de cristaux liquides (E7) ont été utilisés comme matériaux de départ dans le processus de polymérisation/réticulation conduisant à une séparation de phase entre le polymère et le cristal liquide. Le comportement temporel de la transmission optique de ces films a été étudié expérimentalement pendant la période d'exposition à la lumière UV en l'absence de champs externes appliqués. Les courbes de transmission en fonction du temps des films TPGDA/E7 durcis aux UV in-situ révèlent trois domaines : Un premier domaine correspondant à un film transparent ...