PHD, Kent State University, 2023, College of Arts and Sciences / Department of Chemistry and Biochemistry

Liquid crystals are known as the fourth state of matter, and it is found between two condensed phases solids and liquids. Liquid crystals were first discovered in 1888 by an Austrian botanist and the term “Liquid crystals” was termed in 1904 by a German physicist. In the long run wide varieties of liquid crystals are known. In this thesis the classes of discotic and calamitic liquid crystals are covered. They have potential applications as supercapacitors and organic semiconductors. The chapters of this thesis are divided into following topics: 1. Tetrafluoro-tetraalkoxy triphenylene discotic compounds. There is a misbelief amongst researchers that long flexible tails on the periphery of a rigid aromatic core are a prerequisite for formation of discotic liquid crystals (DLCs). In this study we have synthesized triphenylene based liquid crystals which have significantly shorter tails on the periphery of the core and still the mesophase is retained. These molecules defy the classical understanding about discotic liquid crystals. 2. Influence of fluorination on the mesogenicity of 6,7,10,11-tetramethoxytriphenylene compounds. Amongst the short tailed DLCs, 1,2,3,4-tetrafluoro-6,7,10,11-tetramethoxy triphenylene has the shortest tails that can retain the mesophase. In this study, we try to learn about the influence of the extent and position of fluorination on the compounds mesogenicity. 3. Chloro-fluoro triphenylene discotic compounds. In this study we have synthesized triphenylene molecules with only fluorine and chlorine substituents, yet we were able to find mesophases in many of these compounds. These compounds belong to the class of strictly tail free compounds with columnar mesophases. 4. No-tail but larger aromatic core discotic compounds. Since we have a few different sets of short tail or no-tail DLCs based on the triphenylene core, we aim to find this behavior in compounds with a larger aromatic core. In this study, we have been able to synthesize s (open full item for complete abstract)

Committee: Robert Twieg (Advisor) Subjects: Chemistry; Organic Chemistry

PHD, Kent State University, 2019, College of Arts and Sciences / Department of Physics

Nematic liquid crystals are widely used for light management applications due to their anisotropic properties. The guest-host system is formed by combining a nematic liquid crystal “host” with a dichroic “guest” molecule. This mixture exhibits new and useful properties. We can either control the transmission of the light or characterize a new configuration for electrically controlled random laser action. The first project is focused on the dynamic scattering mode in nematic liquid crystals which is considered for various applications to control the transmission of light: notably, their use in therapeutic eyewear. This technology would be useful in the treatment of certain ophthalmic conditions, for example amblyopia and strabismus. Specifically, using this technology to controllably and measurably degrade vision in the stronger eye can lead to improved muscle strength and control in the weaker eye. Using a guest-host nematic mixture we have constructed devices that can be switched between a transparent, “off” state to a scattering state having adjustable cloudiness and/or opacity. The second project is related to the observation of electric field induced random lasing in a dye doped liquid crystal system. There is a continued interest in lasing in dye doped liquid crystals (DDLCs) based on prospects for building compact, all organic, tunable mirrorless lasers, with potential applications ranging from miniature spectroscopic and medical tools to large area holographic laser displays. We investigated a configuration that can provide a “reverse mode” operation of guest host based RLs.

Committee: James T Gleeson Dr (Advisor); Bahman Taheri Dr (Committee Member); Micheal Tubergen Dr (Committee Member); Samuel Sprunt Dr (Committee Member); Edgar Kooijman Dr (Committee Member) Subjects: Materials Science; Physical Chemistry; Physics

PHD, Kent State University, 2018, College of Arts and Sciences / Chemical Physics

Commending topological defects of liquid crystals (LCs) facilitates many configurational simulations and experimental manipulations of active soft matter for electro-optical (EO), optical and photonic applications. In this dissertation, investigation of topological defects in cholesteric liquid crystals (CLCs) enables better visualizing and control unique self-assembly, dielectric and optical properties of CLCs and leads to the development of a fast switching active retarder film based on a CLC with uniform lying helix (ULH) texture, a bistable light diffractive CLC films based on metastable bubble domain (BD) texture, and an in-plane-switching (IPS) LC device based on two-dimensional graphene electrode. We first demonstrate a giant flexoelectro-optic effect (FOE) in a CLC with ULH texture. The electric-field-induced helical axis (HA) rotation of a ULH structure due to flexoelectric coupling is accomplished by the surface-localized polymer network stabilization. A 40 times enhancement in flexoelastic coefficient compared to a conventional CLC materials is achieved by using the CLC based on CB7CB bimesogen. The giant FOE of a polymer-stabilized ULH (PS-ULH) enables the development of an active retarder having high optical contrast and sub-millisecond response time. The second part of dissertation is to investigate topology-mediated optical and electro-optical properties of CLCs with BD texture (CLC-BD) providing unique bistability between the light transmission and light scattering states. The CLC-BD device requires electric field only during switching between transparent and opaque states creating great potential applications as active diffusers and smart windows. An opto-mechanical modulation is demonstrated with a light-sensitive chiral azo-benzene dye doping in a CLC-BD device. To close, the augmentation of EO behavior in a nematic IPS device with graphene transparent electrode is demonstrated. We command the EO switching on photo-lithographically-pat (open full item for complete abstract)

Committee: Liang-Chy Chien Dr. (Advisor) Subjects: Engineering; Optics; Physics

PHD, Kent State University, 2012, College of Arts and Sciences / Department of Physics

Liquid crystal devices are possible because of their large optical birefringence and dielectric anisotropy. They have become a part of modern life with the ubiquitous liquid crystal displays dominating the display industry. However, the need to enhance their physical properties is ever increasing and our research tried to provide as much information as possible to fill this void. In our recent studies, we showed by integrating non-liquid crystalline materials such as specialty particles or well-engineered polymers into a specific liquid crystal host, we could enhance the physical properties of the liquid crystal displays and devices. At the same time, it's possible to change how we perceive and use various types liquid crystals and related devices. In the dissertation, first, we present our work focusing on producing enhanced LC-polymer composites where we integrated custom-made polymer materials into unmodified 5CB to produce fast switching, high transparent LC-polymer composites. We developed high transmittance stressed liquid crystals (HTSLC) optimized for their ultra fast operation in the visible and NIR spectral range. The transmittance that is corrected for front and back surface reflections, of the device is more than 95% at 600nm and 99% in the near IR spectral range. The HTSLC produce large phase shifts. For example, an 18-micron thick HTSLC device can produce more than 1-micron phase shift in 1milli second. HTSLC devices have many potential optical applications for display, adaptable lenses and related electro-optic devices. In the dissertation, as second part, we present our work focusing on enhancing the physical properties of liquid crystals by integrating ferroelectric nano-particles into 5CB, where we achieve minimum of 2deg C and maximum of 4deg C increase in the clearing point of unmodified single component liquid crystal. In addition, we also present how to enhance the dielectric anisotropy and order parameter of the LC and present the results (open full item for complete abstract)

Committee: John West L (Advisor); David Allender (Advisor); Qi-Huo Wei (Committee Member); Elizabeth Mann (Committee Member); Alexander Seed (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering; Experiments; Materials Science; Optics; Physics

PHD, Kent State University, 2009, College of Arts and Sciences / Department of Physics

In part because of its anticipated application for faster and lower power-consuming electro-optic devices, the biaxial phase of nematic liquid crystals, characterized by two optic axes, has long been sought after. We have investigated the existence of thermotropic nematic biaxiality in a relatively new system, liquid crystalline tetrapodes, through dynamic light scattering. Liquid crystalline tetrapodes are formed by the attachment of four mesogenic molecules to a single silicon or germanium atom through flexible siloxane chains. Our results, obtained in various scattering geometries and tested against available theory, strongly support the existence of a biaxial nematic phase. The temperature dependent slowing down of the biaxial order parameter fluctuations indicates that the uni – biaxial transition is weakly first order in a 4-ring tetrapode and second order in a 3-ring homolog. The temperature dependence of the relaxation rates of the biaxial order parameter mode and of the scattered intensity associated with biaxial optic axis fluctuations is explained by a Landau-deGennes model of the free energy. In particular, we have confirmed that the intensity exhibits the expected scaling with the uniaxial and biaxial order parameter magnitudes, for several distinct geometries, in the biaxial phase.Another relatively new class of nematics is the lyotropic chromonic liquid crystals (LCLCs) formed from concentrated mixtures of disc-like dye molecules in water. Because of their potential applications in dye based polarizing and compensating films and in biological sensing, and because of recent analogies drawn between LCLCs and the liquid crystalline phases of DNA solutions, LCLCs are interesting systems to study. Using dynamic light scattering on well aligned samples, we have explored particularly the temperature dependence of the elastic constants and orientational viscosities of nematic Disodium cromoglycate LCLCs. These parameters show a significant anisotropy. In part (open full item for complete abstract)

Committee: Samuel Sprunt PhD (Advisor) Subjects: Physics

PHD, Kent State University, 2005, College of Arts and Sciences / Department of Physics

Dynamical properties of the nematic and isotropic phase of several relatively new bent-core liquid crystals, as contrasted to conventional straight-core (“calamitic”) liquid crystals, have been systematically studied by dynamic light scattering. Objective: Comparison of properties of bent-core nematics with straight-core nematics and search for a biaxial nematic phase due to the bent-core shape Observations: Nematic phases are rather uncommon in bent-core compounds because nematic structure occurs only if the molecules can rotate relatively freely around their long axis, the condition apparently met in only a fraction of bent-core materials synthesized so far. The obtained results show that the elasticity to viscosity ratio for uniaxial bent-core nematics is typically two orders of magnitude lower than for straight-core nematics, due evidently to the large viscosity associated with optic axis distortions in the bent-core case. This result is independent of the normal mode of the director fluctuations probed. In one compound polarized light scattering data reveal fluctuations associated with the biaxial order parameter, occurring as a pretransitional effect on approach to the biaxial smectic-C phase. However, results on a homeotropically-aligned sample of another compound provide preliminary light scattering evidence for nematic biaxiality. Objective: To determine nature of isotropic to nematic phase transition and to measure dielectric fluctuations in the isotropic phase near the transition. Observations: The orientational order parameter fluctuations in the isotropic phase have been studied for the first time in bent-core compounds. Analogous to classic light scattering experiments performed on calamitic liquid crystals, fluctuations in nematic order in bent-core compounds exhibit a mean-field-like critical slowing down on approach to the isotropic-nematic transition from above. The fluctuations are intrinsically several orders of magnitude slower than for typical (open full item for complete abstract)

Committee: Samuel Sprunt (Advisor) Subjects:

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

Discotic liquid crystals are typically described as consisting of a rigid molecular core surrounded by long flexible tails. This work explores a group of tail-free discotic liquid crystals, which possess a liquid crystalline mesophase despite completely lacking tails. These compounds are based on 1,2,3,4-tetrafluorotriphenylene with additional electronegative substituents, and form hexagonal columnar mesophases. We describe their behavior using a combination of thermal analysis, X-ray scattering, charge mobility measurements and molecular dynamics simulations.

Committee: Brett Ellman (Advisor); Robert Twieg (Committee Member); Arkaprabha Konar (Committee Member); Samuel Sprunt (Committee Member); John Portman (Committee Member) Subjects: Physics

MFIS, Kent State University, 2022, College of the Arts / School of Fashion

The aim of this study is to better understand how the construction of hamstring sleeve compression garments can be improved for collegiate track and field athletes with a focus on women athletes in particular. The production of the hamstring garments were produced on a Stoll ADF-3 industrial knitting machine in order to reduce waste and produce the garment more sustainably. Different compression garments were created and analyzed to determine if one can design a sustainable three-dimensional hamstring sleeve that does not limit an athlete's mobility and can alleviate pain. Liquid crystals were applied to the garments to examine how they can provide a visualization of the wearer's hamstring injury. Surveys were used to recruit and gather consensus on athletes' interest and usage of hamstring compression garments and to determine their hamstring health and past injuries in relation to hamstring strains. Kent State University track and field athletes were recruited to test the functionality of the three-dimensional knitted hamstring sleeves to provide critical feedback on overall functionality.

Committee: Linda Ohrn (Committee Co-Chair) Subjects: Design

PHD, Kent State University, 2020, College of Arts and Sciences / Chemical Physics

Spatially variant molecular orientations are central to the functionalities of various liquid crystal applications such as Pancharatnam lens, gratings, command of active matter, and programmable stimulus-responsive morphing of liquid crystal polymers. In this dissertation, I will present a photopatterning technique which allows for high resolution and high throughput patterning of arbitrary molecular orientations by using plasmonic metamasks. Unlike traditional photomasks, the plasmonic metamasks would generate structured light with spatially variant patterns of both intensity and polarization orientations. By projecting such structured light onto photoactive thin films of azo-dyes, orientation patterns can be imprinted in the azo-dyes and then transfer to the bulk of the liquid crystals. By using this photopatterning technique, transmissive/reflective liquid crystal lenses are designed and fabricated. Design principles and advantages of liquid crystal flat optical elements are detailed discussed.

Committee: Qi-Huo Wei (Committee Chair); Oleg Lavrentovich (Committee Member); Elizabeth Mann (Committee Member); Lu Lu (Committee Member); Hamza Balci (Committee Member); Songping Huang (Committee Member) Subjects: Optics

PHD, Kent State University, 2017, College of Arts and Sciences / Department of Physics

This research described in this dissertation comprises three experimental topics and includes the development of an appropriate theoretical framework to understand the various observations in each. In the first part, we present results from angle-resolved second-harmonic light scattering measurements on three different classes of thermotropic nematic liquid crystals: polar and non-polar rodlike compounds, and a bent-core compound. We analyze the data in terms of the “flexoelectric” polarization induced by distortions of the nematic director field around topological defects known as inversion walls, which are analogous to Neel walls in magnetic spin systems and which often exhibit a closed loop morphology in nematic systems. The second part of this dissertation explores the possible existence of a helical polarization field in the nematic twist-bend (NTB) phase of dimeric liquid crystals, utilizing a similar nonlinear light scattering approach. The NTB phase is characterized by a heliconical winding of the local molecular long axis (director) with a remarkably short, nanoscale pitch. According to theoretical conjecture, a helical electric polarization field accompanies this director modulation, but, due to the short pitch, presents a significant challenge for experimental detection. Our study focuses on topological defects, classified as parabolic focal conics, in two achiral, NTB-forming liquid crystals. These defects generate distortions of the polarization field on sufficiently long (micron) lengths to enable a confirmation of the existence of polar structure. We analyze our results with a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a bilinear coupling between the two. The last part of the dissertation focuses on the layer dynamics of thin, free-standing membranes of a smectic-A liquid crystal, with a particular consideration of the surface (interfacial) paramete (open full item for complete abstract)

Committee: Samuel Sprunt (Advisor); James Gleeson (Committee Member); Elizabeth Mann (Committee Member); Antal Jakli (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science; Optics; Physics

PHD, Kent State University, 2015, College of Arts and Sciences / Chemical Physics

Disclination lines play a decisive role in determining the equilibrium structures of topologically constrained liquid crystal systems including cholesteric blue phases, twist grain boundary phases and liquid crystal colloids. The extra energy associated with disclinations is key to stabilizing one particular director structure over another, yet our knowledge of disclination energetics is limited as are characterization methods. In this work, we detail our approach which has focused onbuilding versatile one-of-a-kind instruments for studying liquid crystal systems. This work details the development and use of two novel instruments: an automated maskless photoalignment pattern generator (maskless system) and ad ynamic-cell system that allows for the automated mechanical adjustment of the liquid crystal cell thickness, twist angle and temperature. Both instruments were extensively refined and characterized for maximum performance. In addition, both instruments were designed as versatile platformsfor new research. In this work, we used the maskless system to create novel surface alignments and Pancharatnam-phase devices, and we employed the dynamic-cell system for the generation and characterization of reverse-twist-domain defect loops.

Committee: Hiroshi Yokoyama (Advisor); Philip Bos (Committee Member); Antal Jakli (Committee Member); Elizabeth Mann (Committee Member); Michael Tubergen (Committee Member) Subjects: Chemistry; Physical Chemistry; Physics

PHD, Kent State University, 2012, College of Arts and Sciences / Chemical Physics

This dissertation reports five specific experiments involving in liquid crystal and polymer composites. Before progressing onto the five experimental chapters, the first two introductory chapters cover the fundamentals of liquid crystals, such as liquid crystal phases, order, optics, electrical properties, and applications, as well as a background on liquid crystal polymer composites. First, nematic liquid crystal droplets, doped with liquid crystal monomers, adopted a twisted radial configuration. These droplets were suspended in silicone oil and were subjected to applied electric fields as well as temperature changes before and after polymerization. Second, a nematic liquid crystal exhibited a frozen polarization when a polymer network was present inside the liquid crystal bulk and a strong DC field was applied to the liquid crystal during polymerization. Polymer concentration and DC field strength during curing were varied in order to find the relationship between these variables and polarization effect. Finally, a dielectric study was conducted on these polymer stabilized liquid crystal samples before and after curing. Third, a polymer network was introduced inside a vertical alignment (VA) mode liquid crystal display to reduce the turn-off switching time. The turn-off time as well as contrast ratio was observed in polymer stabilized VA mode displays as the polymer concentration and rubbings along substrate alignment layer were varied. Light scattering studies on these displays and an independent study on reverse mode polymer stabilized liquid crystal displays were also performed and discussed. Fourth, a polymer-stabilized reflective cholesteric liquid crystal displays were created. These displays, consisting of a nematic liquid crystal with chiral dopants and monomers, were light reflecting at zero field, and the liquid crystal helical director was stabilized by the polymer network. When a field was applied and increased, the reflection band shifted from the in (open full item for complete abstract)

Committee: Deng-ke Yang PhD (Advisor); Qi-huo Wei PhD (Committee Member); Liang-Chy Chien PhD (Committee Member); Eugene Gartland PhD (Committee Member); Alexander Seed PhD (Committee Member) Subjects: Chemistry; Materials Science; Physics; Polymers

PHD, Kent State University, 2011, College of Arts and Sciences / Department of Physics

This dissertation addresses three experimental questions. First, the pretransitional behavior of lyotropic chromonic liquid crystals (LCLCs) is investigated in order to gain further insight into the aggregation mechanism and structure. In order to study the pretransitional behavior of LCLCs in the isotropic phase, a high magnetic field is applied perpendicular to the light propagation direction, which induces birefringence in the material; this is called the Cotton-Mouton effect. The aggregates align with the field, which makes it possible to study how the aggregates form in the isotropic phase. The results of this study indicate that multiple optical effects can be induced, which supports the possibility of a complex aggregate structure. The second part of this dissertation explores the possibility of a biaxial nematic phase (Nb). The geometry of the liquid crystal mesogen is important and it is thought that banana-shaped liquid crystals will have an Nb phase. However, contradicting reports on different bent-core materials have not determined whether this phase exists in them. Optical techniques usually rely on a sample cell rubbing treatment to homeotropically align the main director, n, but optical misidentification of Nb could occur if the material is in a tilted uniaxial phase, which appears the same as a homeotropically-aligned biaxial phase. Using a high magnetic field to completely align n and measuring the magnetic field-induced optical phase difference perpendicular to n gives a conclusive way to determine whether a material has non-zero biaxial order. None of the materials studied appear to have an Nb phase. The last part of this dissertation examines director fluctuations in calamitic and bent-core liquid crystals using dynamic imaging analysis. Dynamic image analysis is a relatively new technique where a measurement of nematic phase fluctuations is made in direct space. These measurements are done using a polarizing microscope, heat stage and CCD camera (open full item for complete abstract)

Committee: James Gleeson PhD (Advisor); Samuel Sprunt PhD (Advisor); David Allender PhD (Committee Member); Robert Twieg PhD (Committee Member); Jonathan Selinger PhD (Other) Subjects: Physics

PHD, Kent State University, 2009, College of Arts and Sciences / Chemical Physics

Modern electro-optical applications require low cost, fast operation speed and low weight. Liquid crystals (LCs) are providing all these features, but there are problems still unsolved and there are phenomena still unexplored. In the Dissertation we explored new approaches for electro-optical applications of LCs. We described new designs of LC-based devices as well as shed some light on relatively new phenomena, such as negative refraction and electrically-controlled dynamics of colloidal particles in LCs. The main results obtained in this work are as follows: 1) Electrically tunable amphoteric (negative and positive) refraction was observed in nematic LC. The very existence of negative refraction in LC has been proven. Applications of the demonstrated phenomenon may include, e.g., beam steering devices. 2) Applicability of SmA materials for birefringent prisms useful in digital beam steerers and dual-frequency nematic for fast achromatic polarization rotator based on 45-degree twisted nematic cells has been demonstrated. 3) Applicability of dual-frequency nematic for LC-based lens with a hole-patterned electrode structure, which focal length can be tuned by the electric field from negative to positive values, has been demonstrated. Such a design can be used to achieve fast optical communication between multiple channels, for example, in microlens arrays, in beam steering or scanning devices or for fast non-mechanical zooming in miniature cameras. 4) Behavior of colloidal particles dispersed in a nematic LC and surrounded by hyperbolic-type defects has been explored. We observed a number of interesting effects, such as levitation of particles in the bulk, selective movement of particles toward the opposite substrates according to the orientation of satellite defects and bidirectional motion controlled by electrically-induced backflow. The observed phenomena open the possibility for electrically-driven particles manipulation in LCs. This may result in many practi (open full item for complete abstract)

Committee: Oleg Lavrentovich (Advisor) Subjects: Materials Science; Optics; Physics

PHD, Kent State University, 2008, College of Arts and Sciences / Chemical Physics

Liquid crystal phases composed of bent core molecules have been a fascinating topic in soft matter physics over the last decade. These materials which can form spontaneous polarizations (ferroelectricity) and chiral symmetry breaking with non-chiral molecules incited much interest in the scientific community. Since these early days, much research has been done on the characterization of these phases and their physical properties. In this work, we studied some of these properties by measuring the structural and viscous behavior using small amounts of material. The non-Newtonian flow characteristics of several bent core liquid crystals are characterized using a nanoliter viscometer. We show that many of these phases have viscoelastic behaviors which are fundamentally different from those observed in classical rod like liquid crystals. Finally, we studied the elasticity and dynamics of freestanding filaments which are stable structures in some bent core smectic phases. Characterization of their elasticity by resonance measurements and other techniques are in agreement with models designed to explain their microscopic smectic structures. We show that their viscosity, filament structure and stability, and microscopic structures can be understood by considering the role of steric interactions between molecules and the frustration thereof.

Committee: Antal Jakli PhD (Advisor); Peter Palffy-Muhoray PhD (Committee Member); Eugene Gartland Jr. PhD (Committee Member); Jonathan Selinger PhD (Committee Member); Samuel Sprunt PhD (Committee Member) Subjects: Physics

Doctor of Philosophy, Case Western Reserve University, 1994, Macromolecular Science

In Chapter I, the applications of Nuclear Magnetic Resonance (NMR) spectroscopy to solid polymers are reviewed. In Chapter II, a side-chain polymer liquid crystal (PLC) based on the 4-hydroxy-4′-methoxy-α-methylstilbene mesogen attached through a flexible spacer of eight methylenic units to a poly(methyl acrylate) backbone is studied via solid-state 13C NMR spectroscopy. Molecular dynamics in the MHz frequency regime are characterized as a function of temperature by the spin-lattice relaxation time constant T1. Rotational correlation times (τ c) and activation energies (E a) are calculated for motions at various local sites in the glass and nematic states. Rapid spinning of the methyl carbons occurs on the fast side of the T1 minimum and the motional activation energy does not change at the phase transition. The activation energies of all three sites in the mesogen are nearly equal, indicating a single collective motion. The activation energy of the α spacer carbon is nearly equal to that of the mesogen, and the β spacer carbon is thirty times more mobile. Further flexibility is introduced at the γ and δ positions. In Chapter III, NMR spectroscopy and Fo urier transform infrared (FT-IR) spectroscopy are used to characterize trans-gauche isomerization of methylene groups in a new class of main chain PLCS. The new series of liquid crystalline copolymers is based on the 1-(4-hydroxyphenyl)-2-(2-R-4-hydroxyphenyl)ethane mesogen where R is F, Cl or CH3 and flexible spacers containing an odd number of methylene units. Trans-gauche isomerization is characterized by FT-IR spectroscopy through measurements of the absorbance of characteristically trans bands, and characteristically gauche bands. Trans-gauche isomerization is characterized by 13C NMR spectroscopy through measurements of the 13C chemical shifts in the solid-state. FT-IR spectroscopy shows that an increase in temperature results in an increase in the percentage of gauche isomers for methylene units in both the s (open full item for complete abstract)

Committee: Jack Koenig (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2012, Polymer Engineering

The ultimate goal of this work is to fabricate self-standing polymer lithium electrolytes and flexible reflective liquid crystal displays by first understanding the equilibrium phase behavior of their constituent mixtures. The isotropic phase facilitates processing and allows better control of the final morphology. It is anticipated that ionic conductivity in polymer lithium electrolytes is favored with isotropic morphology which means that initial amorphous structure should be preserved in the final self-standing membranes. On the other hand, phase separation induced by polymerization is a necessary condition to generate cholesteric liquid crystal dispersions. To understand the effect of morphology on the ionic conductivity, a ternary phase diagram of polyethylene oxide (PEO), succinonitrile (SCN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was established. Ionic conductivity was found to improve in the isotropic region containing high concentrations of SCN. Later, polyethylene glycol diacrylate (PEGDA) having a lower molecular weight of 700 g/mol was used in lieu of PEO and a room temperature ternary phase diagram of PEGDA/SCN/LiTFSI was constructed. Isotropic membranes with ionic conductivities between 10-5 S/cm to 10-3 S/cm at room temperature were achieved. Furthermore, membranes fabricated with PEGDA having a molecular weight of 6000 g/mol, SCN and LiTFSI have a higher ionic conductivity of 2.9*10-3 S/cm at room temperature and increase to 10-2 S/cm at 60 C. This material also exhibits stronger tensile strength and modulus that can be further improved with the addition of trimethylolpropane triacrylate (TMPTA) crosslinker. The fabrication of polymer dispersed cholesteric liquid crystals (CLC) was carried out by first studying the phase behavior of EMA/TMPTA/CLC mixtures. Ternary phase diagram of EMA, TMPTA and CLC was constructed in order to identify the isotropic region necessary to select an appropriate precursor mixture. Reflectivity and electr (open full item for complete abstract)

Committee: Thein Kyu Dr. (Advisor); Homero Castaneda Dr. (Committee Member); Robert Weiss Dr. (Committee Chair); Steven Chuang Dr. (Committee Member); Xiong Gong Dr. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2010, Polymer Science

Organic materials are part of the 3rd generation photovoltaics which focus on providing cost-effective energy production and ease of use. Moreover, organic materials are easy to process, are chemically flexible, and are easy to handle. One method to overcome an intrinsic disadvantage in organics, small exciton diffusion lengths, is to utilize π-π stacking in aromatic materials. One example is discotic liquid crystals which can self-assemble to form continuous charge conduction pathways. A new series of porphyrin based discotic liquid crystals had been previously synthesized and had shown photovoltaic efficiencies of 0.7%. This was very high for a potentially unaligned discotic phase. To understand the reason for this, the structure and morphology of these materials was characterized using DSC, WAXD, SAED and PLM amongst other techniques. The alignment of discotic liquid crystals has been problematic in the past due to their high viscosities. Only thermal gradient alignment and magnetic field alignment proved successful in large scale orientation of these materials. This series showed a stable liquid crystalline phase at room temperature and also a metastable solvent induced crystal phase. The peripheral n-alkyl chain length was varied from C8 to C12. The liquid crystalline phase for all samples showed a ribbon-like morphology. WAXD showed a hexagonally packed columnar structure with significant helical ordering within the columns. A coiled coil structure has been proposed as the only possible structure. This stable Col*hh phase was seen in all the samples. This work is the first observed evidence of a coiled coil structure for an achiral discotic liquid crystal. This would indicate that discotic columnar systems mimic biological systems where coiled coils are found commonly. Sample QE12C also showed a unique undulating morphology. To understand the morphology the n-C14 alkyl chain length molecule was investigated. Characterization showed that the undulating phase (open full item for complete abstract)

Committee: Stephen Cheng Dr. (Advisor); Mark Foster PhD (Committee Chair); Dhinojwala Ali PhD (Committee Member); Carri Gustavo PhD (Committee Member); Pang Yi PhD (Committee Member) Subjects: Materials Science; Physics; Polymers

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

Spatial light modulators are a critical technology in optical systems. Liquid crystal on silicon (LCoS) devices are a particular type spatial light modulators used in numerous applications including wavelength selective switches for optical communications, display systems including projectors, 3-D holographic displays, heads up displays in cars, and virtual reality and augmented reality (VR/AR) headsets, and adaptive optics such as optical beam shaping, beam steering, and wavefront correction. Compared to other spatial light modulators, LCoS technology features high resolution and low cost. This work focuses on developing phase-only LCoS modulators for wavelength selective switches, free space optical communications, and holographic display. Traditional LCoS phase modulators suffer from polarization-dependent phase modulation, so development of polarization-independent LCoS phase modulators is an important research topic. This dissertation explores the design, fabrication, and testing of a novel polarization-independent LCoS (PI-LCoS) phase modulator and explores its use in a free space optical transceiver application. The design of the device consists of a silicon backplane, a thin-film polymer quarter-wave plate, and an electro-optically active liquid crystal layer. The inclusion of a polymer waveplate allows for polarization conversion and polarization independent modulation. The silicon backplane uses a specialized pixel circuit to increase driving voltages and provide stable phase modulation. The fabrication process consists of spin coating thin films onto the silicon backplane to form the quarter-wave plate and liquid crystal alignment layers, then a glass cover is used to contain the liquid crystal. Polarization-independent phase modulation was demonstrated through beam steering experiments, a critical function for applications in wavelength selective switches. Applications of the LCoS phase modulator were explored by demonstrating wavefront correction f (open full item for complete abstract)

Committee: Chongchang Mao (Advisor); Kiryung Lee (Committee Member); Shamsul Arafin (Committee Member); Sanjay Krishna (Committee Member) Subjects: Electrical Engineering; Optics

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

Waveguide liquid crystal display (WLCD) is a newly developed transparent display technology. Since polarizers and color filters are not necessary for the WLCD, high transparency is easily reached. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display in waveguide mode due to the total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state and becomes scattering. The incident light is scattered out of the waveguide mode and comes out of the viewing side of the display. We developed a few methods to improve the performance of the waveguide display. First, by using patterned photo-polymerization or patterned ITO electrode, the scattering efficiency of the liquid crystal in the voltage-on state is significantly enhanced. Second, the spatial uniformity of the light intensity of the display is significantly improved by the light waveguide plate. Third, we achieved 8 inch full color transparent light waveguide LCD prototype that utilizes field sequential color (FSC) scheme to display full color images. Fourth, we developed a light waveguide LCD based on the flexoelectric effect using dimer, which exhibits high contrast ratio. Lastly, based on the flexoelectric effect we developed a reconfigurable liquid crystal diffraction grating whose diffraction angle and efficiency can be controlled by the applied voltage. The light waveguide liquid crystal transparent display has the merits of high contrast ratio, suitable driving voltage, and a sub-milli second ultrafast response time. It does not use polarizers and color filter as in conventional LCDs. It also has an ultrahigh tra (open full item for complete abstract)

Committee: Dengke Yang (Advisor); Philip J. Bos (Committee Member); Songping Huang (Committee Member); Sam Sprunt (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science; Optics; Physics