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Ph.D.: University of Illinois at Urbana-Champaign, 1981
Liquid Crystals Physics
The high-resolution x-ray scattering group headed by Dr. Kumar studies structure of new and novel liquid crystals (LC), LC phase transitions, and flow properties. His groups has applied x-ray reflectivity to the study of surfaces and novel non-rubbed alignement layers. His group also dabbles in small angle neutron scattering and heat capacity measurements. He has an ongoing applied effort on polymer dispersed ferroelectric smectic LC displays. In recent years, there have been several efforts to synthesize the long sought-after, achiral ferroelectric smectic phase. They have attempted to use modulations of chemical and physical properties of molecular structure to destroy the inversion symmtery to obtain such a phase. X-ray measurements on samples synthesized by several groups have been subject of high-precision structural investigations by Dr. Kumar's group. It is now becoming obvious that some of the systems investigated hold promise of yielding such phases, most notably triester compounds developed by research groups at Kent State and Case Western Reserve Universities. Ring compounds incorporating chromophores synthesized at North Carolina State University are found to exhibit a long lived metastable longitudinal ferroelectric phase after corona poling.
The anisotropy in x-ray coherence lengths inherent in x-ray experiments has also been exploited in determining the surface roughness anisotropy on spin-coated polyvinylmethoxy-cinnamate and Langmuir-Blodgett films of poly-di-acetylene acid films. Layers of these materials are being used, in Europe and in Ohio, to prepare alignment films which do not require buffing. It has been found that when they are polymerized by linearly polarized UV light, they align liquid crystals just as buffed surfaces do. X-ray reflectivity investigations have revealed that the exposure to polarized UV light causes their surfaces to become rough to different extent in different directions. This casues surface morphology which qualitatively resembles to that of rubbed surfaces indicating that perhaps the physical rather than chemical interactions determine surface anchoring potential. Dr. Kumar is inventor of polymer dispersed ferroelectric smectic liquid crystals (PDFSLC) display technique which he is currently developing for high-information display. PDFSLCs have been demonstrated to be at least three orders of magnitude faster than nematic based displays commonly used today in portable computers. Additonally, they possess bistability and grey scale. Contrast ratio and viewing angle of ferroelectric LC devices are much superior to all other LC displays.
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