New Polymeric films for Smart Windows with Permanent Memory Effect

• Autor(a) principal: Mouquinho, Ana Isabel Machado
• Data de Publicação: 2019
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/84951
• topic: Liquid crystal; PDLC; poly(ethyleneglycol); permanent memory effect; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

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.