Electro-optical properties of polymer-dispersed liquid crystal prepared by monodisperse poly(methyl methacrylate)/fluorinated liquid crystal microcapsules

The effect on the electrical characteristics of poly (methyl methacrylate) (PMMA) and poly (methyl methacrylate – co – butyl acrylate) (PMMABA) containing liquid crystal (E8) as dispersed material, is investigated in terms of electro optical and dielectric relaxation spectroscopy (DRS) technique. This polymer dispersed liquid crystal (PDLC) composite film is sandwiched between two glass slides with a transparent conductive substrate such as indium tin oxide (ITO). The resulting assembly forms an electro-sensitive material that can be switched from a OFF state to a ON state by the application of an external electric field or thermal ramp. In the present investigation PMMA / E8, PMMABA / E8 and PMMA+PMMABA / E8 composite films of 30/70 wt / wt % were prepared by Solution Induced Phase Separation (SIPS) method. Morphological study showed that homogeneous LC phase is embedded in a spongy – like polymer matrix. Electro optical behavior was determined under the condition of an externally applied AC electric field (0-200Vp-p, 50-1000Hz). DRS has been carried out in the frequency range from 20 Hz to 20 MHz and over the temperature range from 24°C to 75°C.The interfacial charge layer effect and qualitative evaluation of distribution of relaxation time is characterized by Cole-Cole model.

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Polymer Dispersed Cholesteric Liquid Crystals With a Toroidal Director Configuration under an Electric Field

Polymers ◽

10.3390/polym13050732 ◽

2021 ◽

Vol 13 (5) ◽

pp. 732

Author(s):

Anna P. Gardymova ◽

Mikhail N. Krakhalev ◽

Victor Ya. Zyryanov ◽

Alexandra A. Gruzdenko ◽

Andrey A. Alekseev ◽

...

Keyword(s):

Optical Properties ◽

Liquid Crystal ◽

Electric Field ◽

Point Defects ◽

Structural Response ◽

Optical Filters ◽

Response Curves ◽

Polymer Dispersed Liquid Crystal ◽

Dichroic Dye ◽

Polymer Dispersed

The electro-optical properties of polymer dispersed liquid crystal (PDLC) films are highly dependent on the features of the contained liquid crystal (LC) droplets. Cholesteric LC droplets with homeotropic boundaries can form several topologically different orientational structures, including ones with single and more point defects, layer-like, and axisymmetric twisted toroidal structures. These structures are very sensitive to an applied electric field. In this work, we have demonstrated experimentally and by computer simulations that twisted toroidal droplets reveal strong structural response to the electric field. In turn, this leads to vivid changes in the optical texture in crossed polarizers. The response of droplets of different sizes were found to be equivalent in terms of dimensionless parameters. In addition, the explanation of this phenomenon showed a comparison of theoretical and experimental structural response curves aids to determine the shape of the droplet. Finally, we demonstrated that the addition of a dichroic dye allows such films to be used as optical filters with adjustable color even without polarizers.

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