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Mesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films

Sharpnack, Lewis Lee
http://rave.ohiolink.edu/etdc/view?acc_num=kent1499949477885501

Abstract Details

2017, PHD, Kent State University, College of Arts and Sciences / Department of Physics.
This dissertation research describes three related projects. The first was an investigation of two de Vries smectic liquid crystal phases that exhibit lower thermal dependence of the smectic layer spacing than the corresponding conventional smectic phases and are well suited for use in electrooptical devices. The second project studied newly synthesized mesogens. This included investigations of several liquid crystalline semiconducting mesogens and a multitude of candidate de Vries smectic mesogens. The third was an investigation of a new non-contact alignment layer of Arsenic Sulfide (As2S3) to anchor the liquid director and use in electrooptical device. In additional to preliminary characterization methodologies such as polarizing optical microscopy and differential scanning calorimetry, two experimental techniques, X-ray diffraction (XRD) and X-ray reflectivity (XRR), were employed. The X-ray studies were conducted using the in-house spectrometers at Kent State University and the synchrotron X-ray source at the Brookhaven National Laboratory. XRR is used to investigate the structure of potential alignment layers. The results provide important insight into the challenges that need to be overcome to develop this alignment material into a viable commercial product. XRD is used to study the structural properties of several members of two new homologous series of liquid crystal compounds. The study of de Vries materials advances our understanding of the role of various molecular moieties on their phase behavior and, most importantly, their relatively temperature independent layer spacing in the Smectic A (SmA) and Smectic C (SmC) phases. This nearly constant layer spacing is critical for developing new fast ferroelectric and electroclinic effect based displays. The Stevenson research group at Queens University synthesized a multitude of new mesogens incorporating a siloxane tail at one end. This moiety is believed to enhance nano-segregation of the molecules and help form de Vries smectic A and C phases. The results indicate that some of the new mesogens exhibit low layer shrinkage that is indicative of the de Vries behavior. The effects of chain lengths and various moieties on the phase behavior is described in detail. These experiments identified several chiral mesogens as viable candidates for use in ferroelectric displays that are currently the subject of further investigations. Many of the non-chiral molecules studied exhibited de Vries or nearly de Vries layer shrinkage, however, these systems would require the addition of a chiral dopant to be used in ferroelectric applications. Three of the chiral siloxane based mesogens displayed ideal de Vries behavior. The smectic layer spacing changed by 1% or less of the total layer thickness for Si3OK11BPO*, Si3OK11BzPO*, and adpc042. These molecules are presently being investigated for device applications and modified with various terminal groups to enhance the miscibility of nano-particle dopants. Structural studies of novel triphenlyene based organic semiconductors mesogens synthesized by the Twieg group were performed. A desirable trait of organic semiconductors is for the ¿-electron orbitals to overlap and requires that carbon rings in adjacent molecules be parallel. Results of X-ray studies of a series of triphenylene molecules showed a hexagonal columnar (ColHex) phase. The diffraction patterns revealed that the lateral intermolecular distance was ~ 3.5 Å, consistent with the stacking of the triphenelene rings. The high-temperature ColHex phase of these materials at nearly 200 °C may also prove useful for high temperature applications. Films of As2S3 have recently been shown to align liquid crystals. This alignment technique, when fully developed, will eliminate the need for traditional mechanically buffed polymer films deposited on substrates, currently used in liquid crystal displays. Their surface roughness was determined in the two planar directions using x-ray reflectivity profiles to facilitate a comparison with other alignment layers that generate liquid crystal alignment primarily because of their anisotropic surface morphology. Our results reveal that As2S3 films develop anisotropic features under irradiation with polarized blue light that are consistent with the changes that occur in other alignment layers when they are “treated” either with mechanical buffing of polymer films or exposure to linearly polarized UV light. These studies also reveal the development of an extensive oxide layer and the ablation of the film under ambient conditions owing to the absorption of oxygen and moisture. This represents a significant barrier to their commercial applications.
Satyendra Kumar, PhD (Advisor)
Elizabeth Mann, PhD (Committee Member)
Hamza Balci, PhD (Committee Member)
Michael Fisch, PhD (Committee Member)
Scott Bunge, PhD (Committee Member)
218 p.
Chemistry; Materials Science; Physics
Reflectivity, liquid crystal, de Vries, ferroelectric, smectic, electrooptic device, display, x-ray diffraction, x-ray reflectivity

Recommended Citations

Citations

  • Sharpnack, L. L. (2017). Mesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1499949477885501

    APA Style (7th edition)

  • Sharpnack, Lewis. Mesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films . 2017. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1499949477885501.

    MLA Style (8th edition)

  • Sharpnack, Lewis. "Mesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films ." Doctoral dissertation, Kent State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1499949477885501

    Chicago Manual of Style (17th edition)

kent1499949477885501
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This open access ETD is published by Kent State University and OhioLINK.