Master of Sciences (Engineering), Case Western Reserve University, 2017, Macromolecular Science and Engineering

Future stimuli-responsive materials – “smart” materials – will focus on introducing new types of stimuli responses into materials and creating materials that can respond to several stimuli in different ways. The effect of each of these focuses will be the introduction of many novel materials with a wide range of functionalities and properties. The aim of this work is the synthesis of such materials using thiol-based networks. The first chapter focuses on an effort to include thermally-responsive shape memory into an aerogel, using a semicrystalline polymer network and Cellulose Nanocrystals (CNCs). The semicrystalline domains of the network served to facilitate the shape fixing of the material and the CNCs were incorporated in an effort to prevent the gel from collapsing out of aerogel form when heated above the crystalline melting temperature. The second chapter centers on work synthesizing a liquid crystalline elastomer (LCE) using 2,6-bisbenzimidazolypyridine (bip) as the mesogen unit and using dynamic disulfide bonds as the crosslinks. Using bip as the mesogen allows the liquid crystalline transitions to be controlled using temperature, UV light, and exposure to metal ions. Including the dynamic disulfide crosslinks allows the material to be reprocessible, healable, and act as an adhesive.

Committee: Stuart Rowan (Advisor); Michael Hore (Committee Member); Gary Wnek (Committee Member) Subjects: Engineering; Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2015, Polymer Science

Linear poly(styrene-b-isobutylene-b-styrene) (l-SIBS) and arborescent poly(styrene-b-isobutylene-b-styrene) (arb-SIBS) are a type of polyisobutylene-based thermoplastic elastomers (PIB-based TPE) characterized by an excellent mechanical, thermal and chemical stability, low permeability and excellent biostability and biocompatibility. PIB-based TPE are prepared by living carbocationic polymerization with sequential monomer addition which allows to obtain narrow molecular weight distribution and to synthesize a wide variety of architectures. These materials have been extensively used for biomedical applications, however they have a unique combination of properties, not available in any other TPE, that make them suitable for potential uses in other areas as well. This work reports the evaluation of three new potential technological applications for l-SIBS and arb-SIBS. In the first part of this work a new method for the preparation of a flexible piezoelectric polymer by incorporating a bent-core liquid crystal (BLC) in a PIB-based TPE, l-SIBS was shown. The polymer composite material containing 10 wt. % of BLC showed a piezoelectric charge constant d33 (~1 nm V-1) greater than commercially available piezoelectric ceramics. Small angle X-ray scattering (SAXS) results show that the liquid crystal–polymer composite becomes aligned during compression molding leading to macroscopic polarization without electric poling. In the second part of this work l-SIBS and arb-SIBS were sulfonated to prepare block copolymer ionomers. The materials were successfully sulfonated to various sulfonation degrees (SD), and characterized for water uptake and ionic conductivity. This modification significantly increased water uptake of both S-l-SIBS and S-arb-SIBS; the associated proton conductivity of the S-l-SIBS increased with the SD, however it did not rise at the desirable levels. For the S-arb-SIBS low values of proton conductivity were obtained, possibly due to the limited solub (open full item for complete abstract)

Committee: Judit E. Puskas Dr (Advisor); Gary R. Hamed Dr. (Committee Member); Mesfin Tsige Dr. (Committee Member); Darrell H. Reneker Dr. (Committee Member); Thein Kyu Dr. (Committee Member) Subjects: Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

Smart materials have significantly varied properties and their various types are used broadly in many different engineering applications. In order to grow the field and promote its long term viability, it is important to develop tools which enable researchers and practitioners to determine the best smart material for the application. Computerized material selection databases and systems have been recently developed by design and materials engineers to help users select the best materials for an application. However, documentation of smart materials is limited, especially for those aimed at the use of these materials in devices and applications. In this dissertation, system-level simulation models and collected material data are compiled in a GUI-based computer software called Polymers and Smart Materials Software (PSMS). This material selection tool encompasses material properties and material-level models as well as systems level smart material applications for a wide range of smart materials. This type of compiled data can expedite the material selection process when designing smart material based systems by allowing one to choose the most effective material for the application. The PSMS tool consists of the following three major sections: 1) Polymers (Polymer types and properties, Polymeric behaviors including dielectric and liquid crystal elastomers); 2) Smart Materials (Piezoelectric Ceramics/Polymers, Shape Memory Alloys/Polymers, Thermoelectrics, Electrorheological and Magnetorheological Fluids); 3) More information (External databases, Cost information, etc.). The software tool offers a wide variety of design and selection features. Material property and performance charts are provided to compare material properties and to choose the best material for optimal performance. The tool is also flexible in that it enables users to categorize material properties and create their own databases. In areas where existing models were inadequate for systems level integra (open full item for complete abstract)

Committee: Gregory Washington (Advisor); Marcelo Dapino (Advisor); Carlos Castro (Committee Member); Mark Walter (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2024, Chemical Engineering

Thermoplastic elastomers (TPE) are a set of materials with characteristics of elastomers and thermoplastics. There is an increasing demand for polymers to be processed into three dimensional porous constructs for tissue engineering. Aliphatic polyester-based, poly(butylene succinate-co-dilinoleic succinate) (PBS-DLS) and polyisobutylene-based, poly(alloocimene-b-isobutylene-b-alloocimene) thermoplastic elastomer copolymers and their development will be presented for end use as biomaterial-based therapies in this dissertation. Electrospun fibrous scaffolds are favored for tissue engineering for their micro-structured networks creating a high surface area to volume ratio and this high interconnected porosity. These properties help mimic natural tissue structure for better tissue integration and diffusion through the network. Applying thermoplastic elastomers as scaffolds offers materials whose material properties can be tailored for specific applications. This dissertation presents work to advance biodegradable aliphatic copolymers for tissue scaffolds, and polyisobutylene copolymers for drug delivery. Cardiac soft tissue regenerations strategies employ biodegradative copolymers for cell delivery. Completely bio-based and biodegradable PBS-DLS copolymers have shown great potential for coiled 3D scaffolds for cardiac applications. This dissertation presents the kinetics of a step enzymatic polycondensation of PBS-DLS copolymers with varying feed ratios. 1H NMR and SEC results found that hydrophobic soft segment DLS was incorporated into the hard segment PBS within the first 3 hours. After which, the pressure was increased during second stage and complete DLS incorporation and high Mn oligomers occurred between 24 and 48 hours. MALDI-ToF analysis showed that the lower molecular weight fractions cyclic formation of long PBS sequences are favored during early stages of reactions. Poly(styrene-b-isobutylene-b-styrene) is currently used as the coating on the Taxus coronary (open full item for complete abstract)

Committee: Nic Leipzig (Advisor); Judit Puskas (Committee Member); Ge Zhang (Committee Member); Bi-min Newby (Committee Member); Donald Visco (Committee Member); Chrys Wesdemiotis (Committee Member) Subjects: Biochemistry; Biomedical Engineering; Chemical Engineering; Engineering; Health Care; Materials Science; Medicine; Nanoscience; Nanotechnology; Surgery

Doctor of Philosophy, The Ohio State University, 2024, Chemical Engineering

Shape memory polymers (SMPs) have seen increased use in soft robotics, actuators, drug delivery, and optics because of their ability to respond to external stimuli in a variety of ways. As a representative class of shape memory polymers, liquid crystal elastomers (LCEs) have seen expanded interest in recent years, owing to their unique ability to reversibly deform to stimuli without the need for outside deformations. LCEs rely on liquid crystals (LCs), which are self-aligning, rod-like molecules that exhibit a phase between solids and liquids, for their unique reversibility. There is an opportunity to increase the usefulness of LCEs through copolymerization and the addition of nanostructures on the surface. In addition, traditional LCEs are hampered in some applications, namely biomedical applications, because of the inherent danger many of them pose to cells. This work seeks to improve LCEs in three main ways: copolymerizing LC monomers, creating nanoscopic surface structures, and templating the LC order into non-LC monomers. By copolymerizing different LC monomers together, we were able to provide a new avenue to control the magnitude and direction of LCE deformations. With the addition of densely packed, nanoscopic surface structures, we enhanced the adhesive force of LCE films increasing their utility in soft robotics. Finally, by templating the order of LCs to non-LC monomers, we created LCE-like materials that exhibit kinetically trapped, reversible deformations with polymers that are better suited for biomedical applications. These three thrusts have expanded the design space for LCEs and have introduced new materials and physical properties.

Committee: Xiaoguang Wang (Advisor); Lisa Hall (Committee Member); Stuart Cooper (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Polydimethylsiloxanes (PDMS) are a versatile class of elastomeric polymers that have properties such as chemical resistance and high strain at break making them suitable for applications including biomaterials, soft robotics, and wearable electronics. Furthermore, the introduction of porosity to PDMS-based elastomers provides additional properties making them advantageous in applications such as separation membranes, strain sensors, and sound dampening acoustics. Specific to acoustic materials, the stiffness and porosity of the material are the two key properties that can be targeted to control the acoustic dampening capabilities. Currently, designing porous PDMS with a range of stiffness is a challenge, and there is a need to develop such systems to access a wider range of acoustic properties that are currently inaccessible. This dissertation provides synthesis routes to obtain porous PDMS materials with the goal of systematically controlling properties such as porosity, pore morphology, and moduli. This goal was achieved by coupling polymerized high internal phase emulsions (polyHIPEs) with thiol-ene click reactions. Each Chapter of this dissertation investigates individual aspects of the polyHIPE process to develop knowledge in the relationship between the emulsion template with the final properties of the materials. We first established how the volume fraction of the aqueous internal phase, surfactant concentration, and thiol-ene ratio of the PDMS-based polymer network impacted the polyHIPE's porosity, pore size, and storage moduli. We show that these low-moduli porous PDMSs were suitable as materials for ultrasonic sound damping by achieving longitudinal sound speeds of ~ 40 m/sec. We expanded these results by investigating a wider range of thiol-ene ratios of the polymer network at a single porosity to obtain larger differences in the moduli of the PDMS polyHIPEs, and obtained low sound speeds of ~ 40-55 m/sec. We next leveraged the orthogonal natu (open full item for complete abstract)

Committee: Neil Ayres Ph.D. (Committee Chair); David Smithrud Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2023, Polymer Engineering

One-way shape memory polymers (SMPs) possess the unique ability to remember a programmed 'temporary shape' and revert to its original shape when exposed to an external stimulus. Typically, SMPs contain two structure-spanning, solid networks; a permanent elastic network that is strained during programming to drive shape recovery; and a temporary network that fixes the programmed shape. The shape-shifting features of SMPs make them useful for a wide range of potential applications, including 4D printing, soft robotics, flexible electronics, soft aeronautical engineering, and biomedical devices. An interesting pathway to develop SMPs is by blending an elastomer and a crystalline small molecule, where the elastomer forms the permanent network (that promotes shape recovery), and the small molecule crystal forms the temporary networks (that promotes shape fixity). Typical examples of these systems include crosslinked elastomers (natural rubber) swelled in fatty acids (lauric acid, stearic acid, and palmitic acid), straight-chain alkanes (eicosane, tetracosane) or synthetic waxes (paraffin wax). However, a drawback of this approach is the blooming and expulsion of the small molecule during shape programming and recovery. This dissertation attempts to focus on semi-crystalline shape memory elastomers developed from blends of high cis 1,4 polybutadiene and reactive monomers (octadecyl acrylate and benzyl methacrylate) or molecular crystals (n-eicosane and n-tetracosane) with the aim being reducing the effect of blooming while keeping a simple fabrication route to develop these SMPs. The synthetic, network, mechanical, thermal, and morphological properties of a series of polybutadiene-based semicrystalline or glassy blends were studied to understand the structureproperty relationships between their permanent and reversible networks. Furthermore, it will be shown that thermally annealed high cis 1,4 polybutadiene also demonstrates thermoresponsive actuatio (open full item for complete abstract)

Committee: Kevin Cavichhi (Advisor); Fardin Khabaz (Committee Chair); Qixin Zhou (Committee Member); Li Jia (Committee Member); Weinan Xu (Committee Member) Subjects: Chemistry; Materials Science; Plastics

Master of Science (M.S.), University of Dayton, 2023, Mechanical Engineering

Adaptive materials with programmable surface topography control can be utilized for selective boundary-layer tripping. Liquid crystal elastomers (LCE) have lately gained significant attention to be leveraged to enable these changes via repeatable and controlled out-of-plane deformations. The LCE can be preferentially aligned with circumferential patterns through the thickness of the film, which yields a predictable conical out-of-plane deformation when thermally activated. These reversible and predictable deployments can be utilized to develop a multifunctional surface designed for bodies in flow. This thesis concentrates on the experimental research of LCE behavior for purposes of active flow control via controlled surface topography. First, the deformations of the 12.7-mm diameter patterned LCE samples were characterized using digital image correlation in a controlled pressure chamber under positive and negative gauge pressures. The LCE's performance was highly dependent upon boundary conditions, specimen dimensions, and imprinted defect location relative to the boundary conditions, thus leading to the refinement of the LCE formulation to allow for a higher modulus. Then, to exhibit the potential for flow control, varying arrangements of representative topographical features were 3D-printed and characterized in a preliminary wind tunnel experiment using particle image velocimetry (PIV). Results demonstrated that a two-row arrangement of 1.5-mm feature height produced an asymmetric wake about a 73-mm cylinder, reducing drag while generating lift. Subsequently, a proof of concept model with active LCE elements was fabricated and tested using a force-balance instead of PIV in a wind tunnel. The results of the conceptual model demonstrated that LCEs exhibit the necessary performance to be used in flow control applications.

Committee: Richard Beblo Ph.D (Advisor); Siddard Gunasekaran Ph. D (Committee Member); Gregory Reich Ph. D (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

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

This dissertation describes stimuli-responsive liquid crystals and elastomers including thermal/electro-active ionic liquid crystal elastomers, UV responsive twist bend nematic liquid crystal dimmers and fast-switching chiral ferroelectric nematic liquid crystals with detailed studies on its nanoscale structures, electrical and optical properties for possible electric, optical and electro-optical applications. In this dissertation, the first preparation, physical properties, and electric bending actuation of a new class of active materials - ionic liquid crystal elastomers (iLCEs) are described. iLCEs can be actuated by low frequency AC or DC voltages of less than 1 V. The bending strains of the not optimized first iLCEs are already comparable to the well-developed ionic electroactive polymers (iEAPs). Additionally, iLCEs exhibit several novel and superior features. For example, pre-programmed actuation can be achived by patterning the substrates with different alignment domains at the level of cross-linking process. Since liquid crystal elastomers are also sensitive to magnetic fields, and can also be light sensitive, in addition to dual (thermal and electric) actuations in hybrid samples, iLCEs have far-reaching potentials toward multi-responsive actuations that may have so far unmatched properties in soft robotics, sensing and biomedical applications. The following two works are the understanding of the structure of the twist-bend nematic (NTB) phase. The first work presents hard and tender resonant X-ray scattering studies of two novel sulfur containing dimer materials for which we simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTB phase the positional correlation length drops. In the second work we use tender (open full item for complete abstract)

Committee: Antal Jakli (Committee Chair); Robin Selinger (Committee Member); Robert Clements (Committee Member); Robert Twieg (Committee Member); Deng-Ke Yang (Committee Member) Subjects: Materials Science; Nanotechnology; Optics; Physical Chemistry; Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Materials Science Graduate Program

In this dissertation, we use the Finite Element Method (FEM) to model surface deformations produced by liquid crystal elastomer (LCE) coatings with different director microstructures. We first study director fields containing arrays of topological defects of integer and half-integer charges. We demonstrate that deformations are driven by competition between bend and splay in the director field, which in turn depend on the LCE film's defect structure. For example, a +1 defect with azimuthal anchoring has a bend-dominated pattern, and therefore, results in an elevation on heating. By contrast, we find that an LCE coating imprinted with a +1/2 defect demonstrates a surface topography whose deformation is a combination of out-of-plane and in-plane displacements. By modifying the defect core structure, we design an LCE coating with switchable topography containing an array of "suction cups" that resemble octopus suckers. Next, we study LCE coatings prepared between photopatterned substrates with antagonistic surface anchoring patterns. We devise a two-step modeling process in which we first minimize the Frank-Oseen Free Energy via a Finite Difference Method (FDM) to obtain a relaxed director field. We import the director field into the FEM code by interpolating the director field from a cubic lattice to a structured tetrahedral FEM mesh. Combination of FDM and FEM opens a new era to study shape morphing material whose director field is of a 3D form and cannot be solved analytically. For example, we investigate samples constructed from substrates with different director field patterns that produce periodic in-plane disclinations. We show that existence of these disclinations can generate temperature-induced switchable topography with microchannels on the surface of LCE coatings. Each channel can have either a single or double valley shape, depending on the position of the disclination lines with respect to the two film surfaces. Finally, we address the challenging (open full item for complete abstract)

Committee: Robin Selinger (Committee Chair); Badel Mbanga (Committee Co-Chair); Yaorong Zheng (Committee Member); Oleg Lavrentovich (Committee Member); Xiaoyu Zheng (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science

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

Over the past few decades, there has been tremendous development on soft materials in soft robotics, energy generation and sensing applications. These soft materials are mostly polymers. Their compliant elasticity, good adaptability to external constraints, and biocompatibility make them suitable for those applications. Further, polymers that respond by changing their shape or size to an external stimulus such as electric field, magnetic field, heat, pressure, pH, and light have great potential for these applications. Among these stimuli responsive materials, electro responsive polymers (electroactive polymers (EAPs)) acquires great attention. Organic electrochemical transistors (OECTs) have attracted great attention since their discovery in 1984 due to their flexibility, biocompatibility, easy fabrication and tunability through synthetic chemistry. As OECTs conduct both electronic and ionic charge, they are suitable for bioelectronic applications, such as recording electric activity of cells and tissues, detection of ions, metabolites, antigens related with various diseases, hormones, DNA, enzymes and neurotransmitter. In my dissertation, I will describe how we developed ionic electroactive polymers (iEAPs) and ionic liquid crystal elastomers (iLCEs) for the applications of soft robotics, energy harvesting (flexo-ionic effect), sensing and organic electrochemical transistors. Firstly, we engineered poly (ethylene glycol) diacrylate based iEAPs for soft robotics application. Here, low voltage induced bending (converse flexoelectricity) of crosslinked poly (ethylene glycol) diacrylate (PEGDA), modified with thiosi-loxane (TS) and ionic liquid (1-hexyl-3-methylimidazolium hexafluorophos-phate) (IL) is studied. In between 2μm PEDOT:PSS electrodes at 1 V, it provides durable (95% retention under 5000 cycles) and relatively fast (2 s switching time) actuation with the second largest strain observed so far in iEAPs. In between 40 nm gold electrodes under 8 V DC volt (open full item for complete abstract)

Committee: Antal Jákli (Advisor); Björn Lüssem (Committee Member); Songping Huang (Committee Member); John West (Committee Member); Robin Selinger (Committee Member) Subjects: Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Materials Science Graduate Program

Three-dimensional (3-D) tissue scaffolds produce suitable environments for cell growth and proliferation for longer periods of time compared to traditional two-dimensional (2-D) tissue culture and, act as appropriate models for the study of cell-cell/cell-scaffold interactions. 3-D models also allow to study cell activities and their functions as well as to evaluate diseases or tissue damage. Liquid crystal elastomers (LCEs) have intrinsic anisotropy and have shown to promote cell alignment and orientation and the presence of liquid crystals (LCs) at a molecular level with and without the use of external stimuli. The work presented in this thesis is the synthesis, design, and creation of 3-D LCEs scaffolds that support several cell lines to promote tissue regeneration. LCEs scaffolds have shown to meet all tissue scaffold requirements to support cell proliferation and growth since they can potentially be biocompatible, biodegradable and their properties, such as porosity and mechanical properties, can be tuned to adapt and match to different cell lines to obtain a suitable tissue. To tune porosity size and density, a salt leaching method was used. Cellulose nanocrystals (a biocompatible additive) were used as an additive to tune the mechanical properties of LCEs to match the young modulus of specific tissues. Once 3-D LCE scaffolds were produced to specifically match neural-like cell lines, we proceed to co-culture neuroblastoma and a glial cell lines (oligodendrocytes). When neuroblastomas are in presence of oligodendrocytes, myelin sheet is formed around the axon of neurons. We observed myelination of neurons during our co-culturing efforts allowing us to study its formation well over several weeks. Our findings will lead researchers on brain degenerative diseases such as Multiple Sclerosis (MS) to have a more appropriate model to quantify, monitor, and find treatments for demyelination and myelination of neurons. Last but not least, in this thesis we will sho (open full item for complete abstract)

Committee: Elda Hegmann (Advisor); Elda Hegmann (Committee Chair); Robert Clements (Committee Member); Richard Piet (Committee Member); Jennifer McDonough (Committee Member); Edgar Kooijman (Committee Member); Torsten Hegmann (Committee Member) Subjects: Materials Science

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2022, Photochemical Sciences

Siloxane polymers are an important industrial commodity due to their chemical, mechanical, and thermal stability and low toxicity. However, studies to recycle siloxanes are still in their infancy. Traditional methods to synthesize polysiloxanes (silicones) involve high capital-intensive and environmental costs using carbothermal reduction. These reactions release excessive global warming gases such as CO2. Therefore, being able to reuse and recycle siloxanes is highly sought after. The first chapter of this dissertation provides a theoretical review of ways to controllably rupture the siloxane bond into known products. Hydrolysis, catalytic depolymerization, thermal depolymerization, and radical abstractions have been the main approaches to imbue the scission of the siloxane bond, resulting in a slew of products. including new polymers, cyclics, or monomeric silanes. This chapter also details the ways in which photodynamic functional groups can be incorporated into siloxanes to impart alternative reuse strategies over complete depolymerization and repolymerization methodologies. Chapter two describes the establishment of an efficient catalytic room-temperature technique for the depolymerization of silicone polymers, elastomers, and resins in the presence of catalytic fluoride in high swell solvents. The products of these reactions give well defined cyclic siloxane units (D4, D5, D6) as verified by GCMS and 29Si NMR. Silicone-rich systems result in the best conversions and the highest quantity of identifiable cyclics, while complex commercial systems resulted in complicated products alongside discernable cyclics. The products are also repolymerized from this process to reform silicones via acid, base, and fluoride catalysis, opening an avenue to large scale use. The third chapter details the expansion of the fluoride catalyzed siloxane depolymerization processes to a photochemically driven method. This approach allows for depolymerization under UV irradiation in a c (open full item for complete abstract)

Committee: Joseph Furgal Ph.D. (Advisor); Laura Landry-Meyer Ph.D. (Other); Pavel Anzenbacher Ph.D. (Committee Member); Malcolm Forbes Ph.D. (Committee Member) Subjects: Chemistry; Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Toledo, 2021, Engineering

Thermoplastic elastomers (TPEs) are a class of materials known for their low Young's modulus and high yield strain. Their applications range from adhesives and seals to automotive parts, footwear, and medical components. This dissertation aims to develop new applications for styrenic TPEs in areas of stimuli sensing and winter safety. First, TPEs with controlled volumetric shape change sensitive to heat and chemical vapors are developed through the concept of dynamic porosity. Dynamically porous films are developed mainly from poly(styrene-ethylene/butylene-styrene) (SEBS) using an eco-friendly CO2 manufacturing method. It is shown that omnidirectional pore size changes above a glass transition temperature (Tg) for polystyrene (PS) physical crosslinks (i.e. 125 °C), which imparts the films with a controlled pore density and a porous-to-solid transition (PST). The tunable PST at a specific temperature is also concomitant with an opaque-to-transparent transition (OTT) useful for indication/detection of temperature. The PST and OTT concepts were further exploited for developments of actuators and vapor responsive films. The second part of this dissertation describes the development of an unconventional and facile strategy for crafting dynamically porous TPEs with an ability to undergo a PST in response to applied mechanical contact pressure at ambient conditions. The PST is shown to be reversible for multiple cycles by applying an in-plane stretch on the activated non-porous films. The PST transition leads to a three orders of magnitude reduction of pore density, resulting in a strong OTT contrast, which can act as a visual indicator for pore reversion and re-generation. Finally, it is shown that the pore reversion can be exploited to locally control the films' mechanical and heat transfer characteristics. Given thousands of injuries involved with ice, sleet, or snow during winter, the development of surfaces with enhanced grip on such slippery surfaces would be deem (open full item for complete abstract)

Committee: Reza Rizvi (Advisor) Subjects: Engineering; Materials Science; Mechanical Engineering; Polymers

PHD, Kent State University, 2021, College of Arts and Sciences / Chemical Physics

We investigate two soft matter systems that display novel behaviors when driven out of equilibrium by internal stresses, fueled by energy derived from the environment. First, we model shape-morphing dynamics of liquid crystal elastomers. We investigate photoactuation in thin polymer films that exhibit continuous, directional, macroscopic me- chanical waves under constant light illumination. These polymer materials deform mechan- ically in response to any stimulus that modifies the strength of their nematic order. Doping the polymer with an azobenzene derivative enables the material to actuate in response to light. The trajectory of mechanical response can be controlled by patterning the orientation of the nematic director field during cross-linking, a process known as “blueprinting”, which defines the local axis of induced contraction. We model the mechanics of photo-actuation via a Hamiltonian-based nonlinear finite element elastodynamics simulation. We find that the underlying mechanism enabling continuous wave generation is a feedback loop driven by self-shadowing, along with coupling between the nematic order and illumination. The model further demonstrates the mechanism by which wave direction and propagation speed depend on the blueprinted director pattern. These results explain experimental observations by our collaborators, who exploited this mechanical wave generation effect to produce robotic devices that undergo autonomous light-powered locomotion. Second, we carry out computer simulation studies of pattern formation in an active ne- matic fluid composed of flexible filaments, modeled as a thin layer of bead-spring polymer chains with active driving forces and thermal noise. We consider filaments that self-propel, representing e.g. gliding motility of filamentous bacteria on a smooth or bumpy surface. We investigate phase behavior and diffusive transport as a function of filament density and bend- ing modulus, and demonstrate that (open full item for complete abstract)

Committee: Robin Selinger (Advisor); Antal Jákli (Committee Member); Helen Piontkivska (Committee Member); Ye Zhao (Committee Member); Oleg Lavrentovich (Committee Member); Jonathan Selinger (Committee Member) Subjects: Physics

Doctor of Philosophy, Miami University, 2021, Chemistry and Biochemistry

Polymer synthesis and modification have become one of the key research areas in recent industrial development. Dynamic chemistry and photochemistry are two different aspects that could benefit polymeric materials to improve their properties. Photochemistry allows polymerization and modifications of thermal-sensitive monomers to be carried out under mild reaction conditions. Photochemical modifications such as photo-labile cleavages often aid preventing side reactions in reactive monomers and protect the fidelity of the polymers. A novel photolabile monomer, 2-{[(benzyloxy)carbonyl]amino}ethyl 2-methylprop-2-enoate (ONBAMA) was synthesized and explored the deprotection under different wavelengths of light. It was found that ONBAMA yield well-controlled polymers and they can be used in post-polymer modifications upon UV irradiation. Often photochemical reactions are carried out using external light sources such as lasers, LEDs, and UV lights. However, the limited penetration efficacy and reaction vessel geometries can limit the efficiency of photopolymerization and light-mediated modifications. The introduction of an internal light generation is an effective way of overcoming these limitations. In the second chapter, a bi-phasic system was introduced employing the chemiluminescence reaction in the bottom phase and photo-induced polymerization in the top layer as a new concept for using internal light sources in polymerization. Phenyl vinyl ketone (PVK) is known as a photo-responsive molecule. Due to the presence of the acetophenone subgroup, PVK is known to undergo Norrish-type reactions. PVK is known to undergo the Norrish type I process under blue light to generate radicals to initiate polymerization and the Norrish type II process to degrade the poly(PVK). The fourth chapter focuses on using the photoinitiation and degradation of the PVK monomers in synthesizing block polymers and photodegradable thermoplastic elastomeric materials respectively. Dynam (open full item for complete abstract)

Committee: Dominik Konkolewicz Dr. (Advisor); Scott Hartley Dr. (Committee Chair); Richard Taylor Dr. (Committee Member); Rick Page Dr. (Committee Member); Zhijiang Ye Dr. (Committee Member) Subjects: Organic Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2020, Polymer Science

Versatile Ring-Opening Copolymerization and Postprinting Functionalization of Lactone and Poly(propylene fumarate) Block Copolymers: Resorbable Building Blocks for Additive Manufacturing. Additive manufacturing has the potential to change medicine, but clinical applications are limited by a lack of resorbable, printable materials. Herein, we report the first synthesis of polylactone and poly(propylene fumarate) (PPF) block copolymers with well-defined molecular masses and molecular mass distributions using sequential, ring-opening polymerization and ring-opening copolymerization methods. These new copolymers represent a diverse platform of resorbable printable materials. Furthermore, these polymers open a previously unexplored range of accessible properties among stereolithographically printable materials, which we demonstrate by printing a polymer with a molecular mass nearly 4 times that of the largest PPF homopolymer previously printed. To further demonstrate the potential of these materials in regenerative medicine, we report the postprinting “click” functionalization of the material using a copper-mediated azide–alkyne cycloaddition. Degradable, Printable Poly(propylene fumarate) Based ABA Triblock Elastomers. Additive manufacturing is rapidly advancing tissue engineering, but the scope of its clinical translation is limited by a lack of materials designed to meet specific mechanical properties and resorption timelines. Materials that are printable via photochemical crosslinking, fully degradable, and elastomeric have proven particularly challenging to develop. Herein, we report the synthesis of a series of poly(propylene fumarate-b-γ-methyl-ε-caprolactone-b-propylene fumarate) ABA triblock polymers using a sequential ring-opening polymerization and ring-opening copolymerization. When crosslinked photochemically using a continuous liquid interface production digital light processing (DLP) Carbon M2 printer, these ABA type triblock copolymers are durable ela (open full item for complete abstract)

Committee: Matthew Becker PhD (Advisor); Dobrynin Andrey PhD (Committee Chair); Wesdemiotis Chrys PhD (Committee Member); Cavicchi Kevin PhD (Committee Member); Willits Rebecca PhD (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2020, Polymer Science

Mechanical and Antimicrobial Properties of Degradable Quaternary Ammonium Compound Thiol-yne Elastomers. Antimicrobial polymers are an important biomedical material for preventing bacterial infections of implanted devices. Antimicrobial activity is frequently granted through surface-functionalization with contact-killing moieties or delivery or biocidal agents blended with the polymer matrix. These methods have drawbacks which bulk-functionalization can overcome. Quaternary ammonium compounds with various alkyl tail lengths were functionalized onto a dithiol monomer for polymerization with a novel alkyl propiolate monomer into degradable thiol-yne polymers with tunable mechanical properties. Tensile properties, cytocompatibility, and antimicrobial activity of these polymers were evaluated to assess their use as elastic biomaterials. Degradable, Mechanically Tunable Tissue Adhesives from Phosphonate-Functionalized Thiol-yne Elastomers. Tissue adhesives are biomaterials used to close skin lacerations, bind bone fragments, and form strong bonds between artificial joint replacements and bone. Commercial tissue adhesives are limited to toxic cyanoacrylates for soft tissue repair and non-adhesive, non-degradable poly(methyl methacrylate) bone cement. A novel thiol-yne elastomer was synthesized with polypropylene glycol segments added to improve solubility in clinically relevant solvents. A phosphonate-functionalized dithiol monomer was also synthesized to see if ionic interactions with the mineral composites in bone could be utilized to improve adhesion. Synthesis and Characterization of Elastic Sulfonate-Functionalized Thiol-yne Polymers for Conductive Composites. Flexible and elastic electronics are a heavily researched field with applications in medicine and technology. Soft, degradable, and elastic materials are needed which can provide both ionic and electrical conductivity. Sulfonate-functionalized thiol-yne elastomers were synthesized and tested for their hy (open full item for complete abstract)

Committee: Matthew Becker (Advisor); Andrey Dobrynin (Committee Member); Kevin Cavicchi (Committee Member); Xiong Gong (Committee Member); Yu Zhu (Committee Member) Subjects: Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2020, Polymer Science

Scientific discovery has constantly revolutionized society. In the last decade (2010-2020), there has been numerous discoveries including detecting the first gravitational waves or revolutionizing the study of ancient DNA. In the last decade, there are countless material science innovations including the emphasis on the materials genome initiative. The U.S federal government placed prominent attention on advance materials development for a secure economy and human wellbeing. However, research and development yielding scientific breakthrough is very slow and challenging process. In order to overcome these challenges and accelerate discovery, combinatorial material science tools can be deployed. The combinatorial toolbox consist of combinatorial libraries and high throughput evaluation. Combinatorial library creation aims to generate systematic and deliberate chaos while high throughput screening aims to test, capture, and organize chaos. In the material science space, combinatorial libraries aim to generate various material samples with high variation. High throughput aims to rapidly test, monitor, and compile data to develop fundamental structure property correlations. This dissertation aims to integrate the areas of combinatorial material science with additive manufacturing material fabrication and utilizes high throughput imaging techniques. In this dissertation, Chapter I provides the historical background on combinatorial material science techniques with an emphasis on material development. Chapter II shows the materials, methods, and instrumentation used in the study. Chapter III introduces direct write additive manufacturing as a combinatorial fabrication technique. Chapter III integrates static mixers for precise placement in 3D printed objects. The fundamental groundwork is established to develop additive manufacturing technique that creates discrete gradients, precise variation, and placement. Chapter IV demonstrates both combinatorial fabrication (open full item for complete abstract)

Committee: Andrey Dobrynin (Advisor); Kevin Cavicchi (Advisor); Yu Zhu (Committee Member); Matthew Becker (Committee Member); Steven S.C Chuang (Committee Member) Subjects: Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2019, Polymer Science

Research into rubber reinforcement using β-sheet nanocrystals in this dissertation is divided into two major parts: thermoplastic elastomer (TPE) and thermoset vulcanizate. The study of β-sheet nanocrystals reinforced thermoplastic elastomers starts from the β-alanine trimer grafted styrene-butadiene rubbers (SBR) with different grafting densities. The nanocrystals in these two samples are rod-like with the longest dimension of a few tens of nanometers. This is in contrast to the fibrous crystals observed in most of the synthetic segmented TPEs. The rod-like nanocrystals are highly effective in reinforcing the elastomers. High strength, and high extensibility are achieved simultaneously. The rod-like morphology observed in the above SBR and in other oligo(β-alanine)-grafted elastomers studied in the Jia laboratory was attributed to the high chain density of a layer of polymer brush covalently attached to the nanocrystal surface. To demonstrate this, β-alanine trimer-grafted polyisobutylenes with different chain densities on the crystal surface were synthesized in order to control the morphology of β-sheet nanocrystals. TEM and SANs were used to confirm the formation of fibrous and particulate crystals in the soft polyisobutylene continuous phase. The SANS data have provided direct evidence of the existence of a layer of brush-like chains on the surface of crystals. The differences in mechanical and dynamic mechanical properties of TPEs containing β-sheet nanocrystals with different morphologies are less significant than expected. The structure change of the nanocrystals during extension is significant, indicated by the hysteretic behaviors of the β-alanine trimer-grafted polyisobutylenes. Surprisingly, IR and DSC indicate a lack of obvious hydrogen-bond breakage and preservation of the β-sheet crystals when the elastomers are stretched to various tensile strains. A fracture recoil model is proposed to explain the reinforcing mechanism of β-sheet crystals. A few (open full item for complete abstract)

Committee: Li Jia (Advisor); Mark D. Foster (Committee Chair); Gary R. Hamed (Committee Member); Abraham Joy (Committee Member); Kevin Cavicchi (Committee Member) Subjects: Morphology; Polymer Chemistry; Polymers