Dielectric spectroscopy and polarizing microscopy in liquid crystal thin film researchWednesday (28.09.2016) 12:30 - 12:45 Part of:
The aim of this work is to present the polarizing microscopy and dielectric spectroscopy as complementary methods to study properties (mainly dynamics and phase changes) of thin films of ferroelectric liquid crystals (FLC). This class of materials is very interesting from practical and scientific points of view due to their potential application in a new generation of liquid crystal displays (LCDs), so-called ferroelectric liquid crystal displays (FLCDs). FLCDs are promising an improvement to a number of technical parameters such as broader colour palette, lower energy consumption, shorter switching time, and others. Ferroelectric liquid crystals as thin layers on polymer-covered glass surfaces, as it is in FLCDs, were under research. The two methods mentioned above are very important in this field of applied science.
Optical microscopy method requires a transparent or semi-transparent sample. In case of thin samples of liquid crystals, optical microscopy becomes an interesting research tool due to the low light absorption by such a sample. Among other optical methods, polarizing optical microscopy is one of the more interesting thanks to its ability to identify various phases (also mesophases) and crystallites of different orientation. For example, crystallization processes can be observed under different conditions, such as rates of temperature or value of electric field applied to a sample. Additionally, the transition temperature between phases can be determined. To do this liquid crystalline samples were placed in so-called ITO (Indium Tin Oxide) electrooptic cell with thin polymer layers.
Another method well-suited to thin samples is the dielectric spectroscopy. This method gives out information on the internal dynamics of a variety of materials. In thin layers, effects related to the interaction between a material and the surfaces are important, and dielectric spectroscopy is a convenient tool for studying these effects. Liquid crystalline materials were studied in the gold coated glass cells and information about the molecular dynamics was obtained.
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