Smart windows with permanent memory effect

Dissertação para obtenção do Grau de Mestre em Engenharia Química e Bioquímica

In this work PDLC films were made with liquid crystal E7 marketed by MERCK®. Two monomers and one oligomer were used, the monomer PE4A (Pentaerythritol tetraacrylate), the monomer TMT (Trimethylolpropane trimethacrylate) and the oligomer AP [Poly(propylene glycol) acrylate]. The PDLC's were obtained by PIPS method and produced by thermal polymerization using a polymerization initiator AIBN. A co-polymerization was studied using different proportions of PE4A and AP. Electro-optical studies were made in order to determine the permanent memory effect of the PDLCs. Best results are for PE4A/AP co-polymerization of 50/50 and 60% of liquid crystal which results in obtained 100% of permanent memory effect. Different techniques were carried out to characterize the PDLCs: Scanning Electron Microscopy in order to study the morphology of the polymer network, Polarized Light Microscopy which allowed to observe the distribution of the liquid crystal molecules in the polymer network before and after the application of an electric field and, with a temperature ramp at 1ºC/min, allows determine the clarification temperature of the PDLC, Differential Scanning Calorimetry to determine the Tg of monomers/oligomers and polymers, the nematic-isotropic temperature of the liquid crystal E7 and of the liquid crystal in the polymer network and viscosity measurements in order to understand if the viscosity can influence polymerization rate and the final matrix structure. Scale-up was development in self-made cells using conductive glasses with polyimide alignment layer. In order to erase the permanent memory effect obtained in the studied PDLCs, a device using Joule heating was tested.

Fundação para a Ciência e Tecnologia - projeto PTDC/CTM-POL/122845/2010