Author: Vinay Joshi

Publisher:

Published: 2018

Total Pages: 213

ISBN-13:

The recent discovery of high-temperature mesophase, also known as the twist-bend nematic phase in liquid crystal dimers (or bimesogens) has triggered interest due to its unique structure-property relationship. Bimesogens consisting of two mesogenic units separated by odd-membered flexible alkyl chain possess a bent molecular formation which results in a low bend elastic constant (K3) and also facilitates flexoelectro-optic response that can be exploited for innovative technological development in the field of displays and other electro-optic devices. In this dissertation, the dynamics of bimesogen-doped chiral nematic liquid crystal (N*LC) during is studied to understand the influence of low K3 as the rod-like LCs undergo Freedericksz transition from bend to splay. The tilt degeneracy in LCs occurring during bend-to-splay deformation of N*LCs switch, the effect is manifested as the optical bounce in the dynamic electro-optic response. The bimesogens, having short flexible spacers tend to enhance the optical bounce in N*LCs and results in a long response time for homeotropic-twist transition. To enable a fast response time, N*LCs are polymer stabilized with surface-localized protrusions that lowers the backflow during electro-optic response and thereby suppresses the optical bounce by 78% and reduces the response time by >90%. In the second part, to further explore the omnipresent property of bimesogenic nematic materials, a fast flexoelectro-optic response in bimesogen-doped N*LCs with an out-of-plane swing in vertical standing helix was proposed and systematic studied with a series of bimesogens reveal the correlation between the flexoelectrically-driven swinging amplitude of the helices in N*LCs and the flexible spacer length in the bimesogens. The giant flexoelectrically-switched tilt leads to a helix-tilt angle up to 53℗ʻ. The experimentally measured maximum flexoelastic ratio (e/K) of polymer stabilized N*LCs was 2.758 CN-1m-1. Moreover, the LC device exhibits sub-millisecond response time (0.43 ms), low electric-field ramping hysteresis and high optical contrast (500:1) between field-on and field-off state. These observations are of considerable scientific and technological importance and will open up new forays into field-sequential-color devices that provide an energy-efficient solution to current color-filter-based display technology.In the third part, a wide spectra color-reflective device based on polymer-sustained conical helix (PSCH) is explored and demonstrated. Apart from the selective reflection of light, the device also demonstrates light-scattering focal conic texture in off-state and transparent homeotropic state at a high electric field. The memory effect produced by a granular polymer network not only mirrors the conical helix but also facilitates a long-range pitch modulation in a cholesteric during the increasing and decreasing of the electric field. A wide color gamut with high spectral purity and uniform structural colors across the entire electrode area is achieved with the PSCH.The last part of dissertation describes the development of a multiplanar volumetric 3D device with time-multiplexed series of 2-D images using a sequential switching stack of reverse-mode polymer stabilized cholesteric texture (R-PSCT) films and digitally synchronized with 2-D image projection. R-PSCT films tend to lose optical clarity in off-state after few switching cycles due to deformation in the polymer network. To investigate the electro-mechanical characteristics of R-PSCT, a systematic study is performed by varying the concentrations of two different reactive mesogens: RM6 and RM257. The optimum composition of reactive monomer for R-PSCT was found to be 80% RM6+20% RM6 that yields the optical contrast of ~ 7, turn-on time 1.1 ms, turn-off time 1.8 ms and wide viewing angle with a cone of 120℗ʻ.