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In the field of the liquid crystals in device applications, the polymer dispersed liquid crystal (PDLC) with permanent memory effect can become feasible in technological applications. Although studies of the liquid crystals in technological applications were extensively reviewed in the literature, not so much has been reported on the permanent memory effect (PME) in PDLCs. PDLCs can change transmittance from a totally opaque state to a totally transparent state during the application of an external electric field. Typically, the opaque appearance returns to the PDLC when the electric field is switched OFF. However, in this work PDLCs have been produced that use the electric field to create a highly transparent state but the transparent state remains even when the electric field is switched OFF giving rise to a permanent alignment state of LC molecules. This property is called a permanent memory effect (PME). For optimizing this effect a series of linear polyethylene glycol di(meth)acrylate and multi-arm polyethylene glycol with linear chains arms extending radially from a central core with reactive (meth)acrylate end groups were synthesized and characterized. The resulting pre-polymers and also some commercial ones were then tested in preparation of PDLCs. The 70 % of PME and the reproducibility even after multiple repetitions of the heating and electric field cycles application make the poly(ethyleneglycol) dimethacrylate of molecular weight 875 g mol-1 the most appropriate pre-polymer in preparation of PDLCs with PME. This effect is also dependent on the thermal polymerization which produces a polymer ball morphology type in the polymer matrix. In addition, PME is also highly dependent on the alignment layer type coating the glass PDLC cell (homogeneous alignment). With the high transparent state permanently displayed at room temperature through PME (70 %), an efficient procedure to allow the PDLC to acquire its opaque state has been achieved. A method of removing the PME has been outlined by Joule effect with the application of the electric current to the conductive layer (ITO) of the glass PDLC cell. This procedure makes the experimental setup to destroy the LC alignment structure simpler and more practical than by radiation heat. Conventional PDLCs need continuity of energy supply for keeping the ON state, which can be a very limiting aspect for many applications. However, PDLCs with PME besides having lower power consumption can be used in digital memory devices based on write-read-erase cycles. For this, a prototype has been assembled as proof of the concept to be used in the digital process of recording information with the binary language.

Dissertation to obtain the degree of master in Bioorganic Polymer dispersed liquid crystal (PDLC) films consist, commonly, on nematic liquid crystal domains dispersed in a polymeric matrix. These composites can be switched electrically from an opaque scattering state to a highly transparent state by an applied electric field. The molecular structure of the polymerisable monomers that can be incorporated as polymeric matrix plays an important role in the performance of PDLCs. Therefore, the aims of this work were to design and synthesise several new monomers that could be polymerised photochemically and thermally to be incorporated as polymeric matrices in PDLCs and investigate the influence of the molecular structure on the performance of these devices. Several monomers were synthesised in order to achieve better miscibility between the liquid crystal and the monomers during preparation of PDLC films. For this purpose, the monomers were synthesised so as to mimic some structural elements of the E7 liquid crystal molecules. Thus, several aromatic mono- and dimethacrylates with and without a linear chain spacer with five methylene units, as well as vinylic monomers were successfully synthesised. Mild and solvent freeprocedures were developed with reaction times as short as 1 to 5 min, using microwave irradiation. The structures of all isolated monomers were supported by 1H NMR, 13C NMR and FTIR spectroscopy, elemental analysis and melting point. Of all the synthesised monomers, the monomers that included in their structure aromatic rings bearing a cyano group and/or a linear chain spacer with five methylene units were fully characterised due to their higher molecular structure affinity with the E7 liquid crystal molecules. In order to evaluate the effect of these groups, these monomers were compared with those of similar structure but without the respective groups. Thus, DSC and POM with temperature ramps were used for the thermal characterisation of the monomers. The structural morphologies of the polymeric matrices were characterised by SEM. The monomers were also copolymerised with glycidyl methacrylate and the molecular weights of the resulting polymers were evaluated by GPC. The electro-optical properties of the PDLC films were determined by measuring the voltage dependence on the transmitted light. Fundação para a Ciência e Tecnologia - Project PTDC/CTM/69145/2006