Joule-Heating Effect for Erasing Information in PDLCs Devices with Memory

• Autor(a) principal: Malta, José Francisco Rodrigues
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/19336
• topic: PDLC; Liquid crystal; Joule heating-effect; Permanent memory effect; Capacitance; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

The main objective of this work is trying to find the best way to erase written infor-mation in PDLC devices with memory by Joule-heating effect, and how this can be applied on a smart window system. Then, a mixture composed by 70% liquid crystal E7 by Merck and 30% oligomer PEGDMA875 was used in several cells with different properties. First of all, DSC studies were done for E7, oligomer and mixture E7/oligomer to deter-mine their thermal properties. Then, six different cells with different alignment types were test-ed in an electro-optical (EO) study. It was verified that the Permanent Memory Effect (PME) is only present in cells which glasses have planar alignment. AFM and SEM analysis were done on glasses to determine how the planar alignment can affect the mixture polymer/liquid crystal and thus the PDLC performance. On rubbed glass-es some stretch marks were detected where the mixture follows their preferred direction. For these cells, capacitance studies with temperature were done for three types of dielectrics inside: with no dielectric (empty), with liquid crystal, and with polymer. Afterwards, the same study was also done for cells with PDLC but this time with a transmittance measuring along the tem-perature. The capacitance and transmittance curves can give the information about the clarifica-tion temperature (Tc). This will be the temperature where the opaque-transparent transition can be observed. It was also verified that after EO study the capacitance values increases and when the written information is erased they return to previous values. After known each Tc, the devices were heated by Joule-Heating Effect with different levels of current, measuring the capacitance variation. This study was done first for the cells before EO study (with no written information) to find which current intensities can reach the Tc and then for the cells after EO study (with written information). Only a group of current intensi-ties can completely erase the written information. This can be verified when, during heating, the Tc is reached, and if the capacitances values in the end of the heating are equal to values before EO study.