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The additive effects in matrix dispersed liquid crystals
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Orientador(es)
Resumo(s)
The main objective of this work was to optimize the structure of a matrix that will
support a nematic mixture of liquid crystals, known as 𝐸𝐸7 from Merck, in order to produce a matrix dispersed liquid crystal device with good electro-optical responses.
The composites are based on monomers, such as tri(ethylene glycol) dimethacrylate
and poly(ethylene glycol) dimethacrylate with typical molecular weight of 875 𝑔𝑔. 𝑚𝑚𝑚𝑚𝑚𝑚−1 with two different types of polymerization, a thermal polymerization
with initiation by α,α’-azoisobutyronitrile and a photochemical polymerization with
initiation by p-xyleneN,N diethyldithiocarbamate.
To do that, some additives have been used as a way to format the shape and the size
of the liquid crystal microdroplets and to avoid its coalescence and, therefore,
optimizing the performance of the device as being able to electro-optical application.
Octanoic acid, ethylene glycol, triton X-100, cetyl trimethyl ammonium bromide and
sodium dodecyl sulfate have been used as additives to the systems.
Different aspects were investigated, such as the study of the dynamics of the transition
ON/OFF state using a high-frequency alternate voltage and the attempt to minimize
and maximize the liquid crystal anchorage breaking to the polymer matrix observed
when tension is applied. The polymer morphology and the composites synthesized
were analyzed by polarized optical microscopy and scanning electron microscopy and those results were related with the electro-optical response curves of the composites in study.
The best results were obtained with the system containing the triton X-100 as an
additive, thus this system was analyzed with additional studies of differential scanning
calorimetry, dielectric relaxation spectroscopy and a scanning temperature through polarized optical microscopy.
Descrição
Dissertation presented at Faculdade de Ciências e Tecnologia from Universidade Nova de Lisboa to obtain the degree of Master in Chemical and Biochemical Engineering