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

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Polyurethanes (PUs) are a broad class of versatile and widely used polymers that make up an important platform in applied polymer chemistry. Their tunability and flexibility lends their use in many applications such as textiles, cushioning, insulation, and biomedical devices. Additionally, polyurethanes have been developed as shape memory polymers (SMPs). The physical properties such as glass transition temperature, storage moduli, hydrophilicity, and bulk morphology were systematically tuned to meet the needs of various potential applications. First, hydrogels were coated around a porous SMP produced from lactose functionalized polyurea-urethanes. The polymers were studied for their biocompatibility, swelling capabilities, and shape memory properties. These results indicate that hydrogels can be composited with SMPs without inhibiting the shape memory behavior. Strategies to combine the properties of both polyurethanes and hydrogels were also studied. To this end, polyurethane hydrogels were synthesized through copolymerization of a novel lactose monomer with PEG and diisocyanate monomers. Swelling studies the incorporation of hydrophilic lactose groups was essential in imparting the PU with sufficient hydrophilicity for substantial swelling in water. Subsequent sulfation of the lactose rings gave rise to high-swelling polyelectrolyte hydrogels. The effects of PEG molecular weight, degree of crosslinking and ionization, and resulting swelling behaviors were studied. Building on this work, we exploited the known hydrophilicity of lactose to design dual responsive shape memory PUs. Shape memory polyurethanes were prepared through copolymerization of a novel lactose monomer with PEG and diisocyanate monomers to form films rather than hydrogels. The mechanical properties of the shape memory films were shown to be dependent on the molecular weight of the PEG chains. The incorporation of lactose into the PU network endows the material with moisture resp (open full item for complete abstract)

Committee: Neil Ayres Ph.D. (Committee Member); James Mack Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member) Subjects: Chemistry

Master of Science in Engineering, Youngstown State University, 2022, Department of Civil/Environmental and Chemical Engineering

Additive manufacturing (AM) commonly referred to as 3D printing is a method of manufacturing three-dimensional parts in a layer-by-layer fashion. Common materials used in this process are polymers, metals, and ceramics. Nowadays, AM is utilized for more than just traditional structures - it is used to fabricate and create nontraditional designs. Additive manufacturing is associated with various industrial manufacturing processes and innovations including maintenance, repairs, and product design. Among the different applications of this process, the production of 3D printed morphing systems and parts for batteries represents an attractive approach for yielding high-performance structures. Non-metallic morphing components are commonly constituted by shape memory polymers (SMPs), which are actuating materials that can respond to thermal, electrical, or chemical stimuli. Here, SMPs were constructed by incorporating two different blends of photopolymer resins in a Vat Photopolymerization process. The printed SMPs were subsequently electroplated with copper to yield a conductive morphing structure for applications such as sensors, actuating systems, and functional antennas. The present work investigated the adaptability and functionality of the copper-plated 3D printed parts as morphing antennas capable of providing a multi-radio frequency. Additionally, this research program investigated the production and performance of 3D printed LiFePO4 parts via Vat Photo Polymerization to be used as electrodes on additively manufactured energy storage devices. This effort represents a novel approach to further expanding the production of customized batteries.

Committee: Pedro Cortes PhD (Advisor); Vamsi Borra PhD (Committee Member); Frank Li PhD (Committee Member) Subjects: Aerospace Materials; Chemical Engineering; Materials Science; Polymers

Master of Science, University of Akron, 2020, Polymer Science

Nature exhibits phenomenons where active shape changes can occur in response to its environmental conditions. Notable examples of such shape changes are the opening and closing of the Venus flytrap to capture prey and the microscopic shape changes in the skin layers of cuttlefish that enable its macroscopic color change. This biological intelligence has unlocked a new class of smart materials, namely, Shape Memory Polymers (SMPs) which exhibit special functions in response to external conditions.[1] Shape Memory Polymers (SMPs) are materials that can transition from a fixed, original shape to a temporary shape and vice versa upon triggering or removal of external stimuli. These intelligent shape transformations are usually thermally induced, can also be a direct heating or indirect heating (photo-, electro- and magneto-thermal induction) and light or chemical impetus (change in concentration, pH, solvent etc.)[1],[4] Polyester urea (PEU) is a class of bioresorbable polymers which have been widely used for applications such as tissue engineering, surgical repair of bone defects, drug delivery systems, etc. [2],[3]. PEUs based on different amino acids with varying diol chain lengths have been thoroughly studied in the past. In this study, we conducted experiments to characterize the change in shape memory properties of L-valine based PEUs upon degradation. These PEUs demonstrated ideal phase transition temperatures, i.e. physiological temperature, to be used as an implantable SMP. The PEU in this study was subjected to thermomechanical cycles on Dynamic Mechanical Analysis (DMA) to characterize for its shape memory properties and Size Exclusion Chromatography (SEC) was employed to record the change in degradation over time. It is expected that the result of this study will provide a PEU demonstrating good shape memory effect upon degradation which would make it an ideal candidate as an implantable SMP. References: [1] A. Kirillova, L. Ionov, J. Mater. Chem. B, vol. (open full item for complete abstract)

Committee: Tianbo Liu (Committee Member); Abraham Joy (Committee Member) Subjects: Polymers

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

4D printing is an emerging technology that combines 3D printing and stimuli-responsive materials. The core idea of 4D printing is `3D printing +time', where the geometries, properties and functionalities of 3D printed structures can evolve as a function of time. While simple shape transformation has been achieved in most 4D printing systems, more limited attention has been paid to 4D printing with multi-functionality or complex shape transformation patterns. However, these properties are of critical importance for advanced applications. For example, sequential shapeshifting is useful for consecutive motion and actuation of soft robotics. High flexibility and extensibility are desired properties in soft electronics and some biomedical devices. To address these limitations, we developed functional 4D printing based on rational designs of shape memory polymers at molecular, morphological and geometrical levels. First, we achieved the first triple shape memory polymer by digital light processing (DLP) 3D printing. We prepared DLP printable resins containing an ion-pair comonomer and acrylates, and obtained ampholytic ionomers through photocuring. These ionomers featured microphases-separated morphology, which generated two glass transition temperatures (Tg) associated with the ion-rich and ion-poor domains. The well-separated Tgs produced excellent triple shape memory effect. The influences of neutral comonomers on microphase separation and Tgs were investigated systematically by dynamic mechanical analysis (DMA) and atomic force microscopy (AFM). Finally, sequential shapeshifting through different shape evolution pathways and its application in microfluidics were demonstrated. Second, we 4D printed a highly extensible, self-healing shape memory elastomer based on fused filament fabrication (FFF) 3D printing. The material was made of a thermoplastic elastomer, polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS), and a semi-crystalline thermoplastic, (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Li Jia (Committee Member); Yu Zhu (Committee Member); Weinan Xu (Committee Member); Jae-Won Choi (Committee Member) Subjects: Chemical Engineering; Mechanical Engineering; Polymers

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

Shape memory polymers (SMPs) are a type of material capable of indefinitely holding a deformed shape and recovering their original shape upon the application of an external stimulus, such as temperature. SMPs contain at least two networks consisting of a permanent crosslinked polymer matrix and a second reversible, shape fixing network. These networks could be chemically bonded in single chemistry systems such as block copolymers containing elastic and glassy or crystalline phases or be blended together through elastomer and crystalline small molecule mixtures. This dissertation primarily focuses on SMP blends derived from fatty acid-elastomer blends with the aim being to further simplify the fabrication of these materials. The mechanical, thermal, and morphological properties of a series of different blends, along with several styrenic block copolymers, were studied to understand the structure-property relationships between their permanent and reversible networks. In Chapter II, fatty acid swollen natural rubber shape memory polymers were investigated as a function of swelling extent, acid polarity, and applied deformation. The fatty acid-rubber systems demonstrate a 40-50 wt% effective fatty acid solid phase loading range where the fixity of a programmed shape remained > 95% while maintaining structural integrity. The strength of the crystalline fatty acid networks were determined through dynamic mechanical analysis (DMA) moduli measurements where, under large uniaxial deformations, the modulus of the fatty acid was found to increase compared to the unstrained material. This was consistent with preferential alignment of crystal platelets along the strain direction as determined by small angle X-ray scattering (SAXS) measurements. In Chapter III, SMP foams were fabricated by immersing a polyurethane foam inside stearic acid-isopropyl alcohol solutions of varying concentration. Samples were programmed using DMA or a compression press. It was determined that f (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Mukerrem Cakmak (Advisor); Li Jia (Committee Member); Jiang Zhe (Committee Member); Sadhan Jana (Committee Chair) Subjects: Polymers

Master of Sciences (Engineering), Case Western Reserve University, 2019, EMC - Mechanical Engineering

Shape memory smart materials that are self-fixing and auto-adaptive upon the application of a stimuli could play a key role in the manufacturing of next-generation intelligent technologies. In particular, the development of shape memory polymer composites that exhibit variable thermal conductivity upon straining requires an in-depth understanding of the material, mechanical, and thermal properties of the respective polymer and filler materials as well as the composite itself. For this work, a multi-block thermoplastic polyurethane co-polymer is used as the shape memory matrix with cellulose nanocrystals (CNCs) and carbon nanofibers (CNF) as fillers. The shape memory polymer composite is thermally characterized and its behavior explained using knowledge of filler alignment and crystallinity that vary upon straining.

Committee: Alexis Abramson (Committee Chair); Yasuhiro Kamotani (Committee Member); Chirag Kharangate (Committee Member); Steve Hostler (Committee Member) Subjects: Aerospace Engineering; Materials Science; Mechanical Engineering; Polymers

Doctor of Philosophy, University of Akron, 2018, Polymer Engineering

The past decade has witnessed remarkable advances in the performance and capabilities of shape memory polymers (SMP), which are stimuli-responsive materials that change its shape upon exposure to the appropriate external stimulus, such as temperature. This responsive nature of SMP brings many potential applications, such as actuators, biomedical devices, and clinical products among others. One promising new class of SMPs is ionomers and their composites due to their ease in processability and great mechanical properties. In this work, ionomer-based SMPs and their composites were successfully applied in films and 3D printing to enable the investigations of the shape memory behavior from the nanoscale to macroscale. Physiological SMP with a transition temperature at 37°C, which is human body temperature, applies to many potential applications in clinical or skin-contacting products. The physiological SMP was assembled by mixing zinc salts of sulfonated poly (ethylene-co-propylene-co-ethylidene norbornene) (Zn-SEPDM) ionomer with lauric acid (LA), and the SMP composite shows a shape memory transition temperature at ~37°C. The physiological SMP solution was cast into film on roll-to-roll, which provides a fast, stable, and continuous processing of the material. The shape memory behavior of the film product was studied. The fixity was constant at ~80% for 5 shape memory cycles. The first cycle recovery (R=58%) at 37°C was much lower than subsequent cycles recovery (R>82%). It was also found that a lower storage temperature at 6°C for programmed film sample could improve both the fixity and recovery. For the programmed film after one week, sample with storage temperature at 19°C was F=85%, R=65%, while the sample with storage temperature at 6°C was F=90%, R=75%. Microscopic and nanoscopic scale textures and patterns on surfaces provide a handle to modulate properties, such as surface wetting, optical properties, and dry adhesion. Creating surface textures and patterns (open full item for complete abstract)

Committee: Robert Weiss (Advisor); Bryan Vogt (Advisor); Kevin Cavicchi (Committee Chair); Eric Amis (Committee Member); Qixin Zhou (Committee Member) Subjects: Engineering; Plastics; Polymers

Master of Science, University of Akron, 2018, Polymer Engineering

Silicone rubber is widely used as an elastomer. This thesis investigates the fabrication and material properties of silicone rubber blended with some inexpensive fillers. The section of this thesis focuses on cornstarch-silicone rubber blends. In acetoxy cured silicone rubber, cornstarch has good compatibility and is able to blend well with the silicone resin. Samples were prepared by simple physical mixing. The crosslinking degree and other mechanical abilities can be investigated as a function of the weight percent of cornstarch and water. The second section of this thesis focuses on shape memory polymers. Shape memory polymers were fabricated by mixing acetoxy silicone with crystalline small molecules. The solid-liquid transition of the small molecule is able to generate reversible solid networks, which enable the shape memory effect. The shape memory effect properties tested as a function of the weight percent of the small molecule in samples. With increasing weight percent of the small molecule, the fixity is increased to ca. 99% and the recovery decreased to ca. 87%. Based on these tests, an optimum blend formulation is found, which shows the best shape memory performance can be found and repeatability through several test cycles. Due to the differences in the interaction degree between the small molecule and the silicone rubber, the choice of the small molecule is also an important factor to influence the shape memory effect.

Committee: Kevin Cavicchi (Advisor); Nicole Zacharia (Committee Chair); Erol Sancaktar (Committee Member) Subjects: Polymer Chemistry; Polymers

Master of Science in Polymer Engineering, University of Akron, 2017, Polymer Engineering

Quaternary ammonium compounds (QACs) are a mainstay of anti-bacterial materials which are the most effective bactericide agents against microorganisms at a neutral or slightly alkaline PH with generally low concentration. They also have numerous applications as surfactants and disinfectants in a variety of industrial and consumer applications. 10-Carboxy-N-decyl-N, N'-dimethydecyl-1-ammonium bromide is a kind of QACs which has the similar gelation ability as 12HSA because of the ion-pair effect. Nucleophilic substitution was the reaction for synthesizing this quaternary ammonium bromide compound and 1H-NMR was used to characterize the final dried products in this thesis. Then the thermal characterizations of samples were measured by TGA, DSC. In order to fabricate QAC organogelators, different solvents were mixed with QAC with different concentration and only DMSO and ethylene glycol succeeded. The final step of this experiment was to observe the crystalline formation process and structure of gels by POM. The second study focuses on shape memory polymer (SMP), a novel kind of smart material which can remember its original shape and has lots of advantages, such as high elastic but low temperature deformation, low density, low cost, better potential biocompatibility and various external stimuli more than temperature. Bilayer SMP is fabricated by creating inhomogeneous phase of material to achieve deformation purpose without external forces. This thesis first introduces the fundamental understanding of SMPs history, structure, stimulus method and categorization, and the principle of bilayer SMPs. The SMPs were fabricated with commercial readily cross-linked natural rubber bands and stearic acid in this experiment. Next, the iso-strain stress shape fixity and recovery of SMPs varying with different Stearic Acid wt%, stretch time and stretch strain under cold-drawing conditions are presented. This differs from the typically SMP processing where the sample is heated abo (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2017, Polymer Engineering

The delamination and debonding between SMA and PMC in various test types and composite lay-ups was studied in this thesis research. In the first part of this study, a pull-out test was designed and implemented in which a strip of SMA was pulled out of a PMC coupon in tensile mode. It was found that the default bond between SMA and PMC resulted in a mixed-mode pullout and shape memory effect of the SMA, while addition of adhesives halted pullout progression and invoked only shape memory effect of the SMA until total adhesive failure. In the second part of the study, two adhesives and three PMC lay-ups were used to fabricate SMA strips embedded within PMC coupons. These specimens were monitored with modal acoustic emissions during tensile testing; these AE signals were then plotted against the stresses in the systems along with break locations during sample failure. It was found that the lay-ups of the plies within the PMC had a greater effect on the strength of the samples than adhesives used, while the use of acoustic emissions successfully predicted location failure throughout tests. The final part of the study focused on the interlaminar fracture toughness properties of PMC laminates with embedded SMA. Two adhesives were utilized in Mode I and Mode II test coupons. Specimens were monitored with acoustic emissions during testing: these AE signals were then plotted against the applied loads in the systems. For Mode I interlaminar fracture toughness, the addition of adhesives was necessary to produce reliable results. From these results, “Ply-bridging” was observed between the SMA and PMC in which the propagating crack traversed the SMA during testing, inflated the toughness values of specimens during testing. AE signals of these tests showed that the addition of adhesives had a negative effect on the generated acoustic signals. For Mode II interlaminar fracture toughness, the addition of adhesives were detrimental to the bond between SMA and PMC. This was refl (open full item for complete abstract)

Committee: Sadhan Jana (Advisor); Alamgir Karim (Committee Chair); Gregory Morscher (Committee Member); Erol Sancaktar (Committee Member); Robert Goldberg (Committee Member); Wieslaw Binienda (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Polymers

Master of Science, University of Akron, 2017, Polymer Science

The biomedical applications of shape memory polymers (SMPs) have been actively investigated. a-Amino acid-based poly(ester urea)s (PEUs) with excellent synthetic flexibility and performance (i.e. highly tunable properties, non-toxicity and controlled degradation capability) have been demonstrated as competitive SMPs for biomedical applications. With an aim to obtain tunable shape memory behavior and broaden the family of PEUs, we developed a series of L-alanine based PEUs with different linear diols and PEU random copolymers composed of two different diamine monomers based on L-alanine and L-valine. The polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile testing. The characterization results showed that the polymers were successfully synthesized. Changing the diol chain lengths in the alanine-based PEUs and the feed ratio of two different diamine monomers in the PEU copolymers resulted in a wide range of thermal, thermo-mechanical and shape memory properties due to the polymer chain mobility. For the alanine-based PEUs, increasing the length of linear diols, the glass transition temperature (Tg) was decreased. The shape memory effect of the alanine-based PEUs was demonstrated. For the PEU copolymers, by increasing the content of the valine-based diamine monomer, the Tg was decreased and the shape memory performance was enhanced, as a result of enhancing molecular chain mobility. Overall, by employing L-alanine, we have broadened the family of PEUs and the copolymer system has also been demonstrated as a precise approach to tailor properties to fit custom needs.

Committee: Matthew Becker (Advisor); Abraham Joy (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 2016, Macromolecular Science and Engineering

CHAPTER1: A synthetic polymeric lens was designed and fabricated based on a bio-inspired, “Age=5” human eye lens design by utilizing a nanolayered polymer film-based technique. The internal refractive index distribution of an anterior and posterior GRIN lens were characterized and confirmed against design by µATR-FTIR. 3D surface topography of the fabricated aspheric anterior and posterior lenses was measured by placido-cone topography and exhibited confirmation of the desired aspheric surface shape. Furthermore, the wavefronts of aspheric posterior GRIN and PMMA lenses were measured and simulated by interferometry and Zemax software, respectively. Their results show that the gradient index distribution reduces the overall wavefront error as compared a homogenous PMMA lens of an identical geometry. Finally, the anterior and posterior GRIN lenses were assembled into a bio-inspired GRIN human eye lens through which a clear imaging was possible. CHAPTER 2: A nanolayered polymer films approach to designing and fabricating gradient refractive index lens (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry has been demonstrated to produce a new class of gradient index optics. This approach utilized nanolayered polymer composite materials from polymethylmethacrylate (PMMA) and a styrene-co-acrylonitrile copolymer (SAN) with a tailorable refractive index intermediate to bulk materials to fabricate discrete gradient refractive index profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is also described. A review of a collection of technology-demonstrating nanolayered GRIN case studies is which include: optical performance of an f/# 2.25 spherical GRIN plano-convex singlet 1/10 the weight of a similar BK7 lens and a bio-inspired aspheric human eye lens. Original research on the fabrication and characterization of a Lunebu (open full item for complete abstract)

Committee: Eric Baer Prof. (Committee Chair); Alexander Jamieson Prof. (Committee Member); Andrew Olah Dr. (Committee Member); Donald Schuele Prof. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2014, Polymer Engineering

The primary focus of this dissertation is to understand the thermo-mechanical properties that govern shape memory in rubber blends. An ideal shape memory polymer (SMP) has a large entropic component that drives shape recovery with a distinct transition mechanism to control the recovery conditions. Polyisoprene rubber is highly elastic and shows shape memory behavior through strain induced crystallization above its glass transition temperature. However, this transition temperature is below 0°C and not suitable for most applications. Shape memory blends can tailor the transition temperature through selection of the switching phase. Most SMP blends require complicated synthesis routes or intensive compounding which would be inhibitive for production. A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Thermal, microscopic studies showed that stearic acid formed a percolated network of crystalline platelets within the natural rubber. Further investigation of the material interactions was carried out with a low molecular weight polyisoprene analog, squalene, and stearic acid gel. Tensile tests on the rubber band demonstrated the thermo-mechanical effect of swelling with stearic acid. Low hysteresis was observed under cyclic loading which indicated viability for the stearic acid swollen rubber band as an SMP. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acidand fixation below that point. Under manual, strain-controlled tensile deformation, the shape memory rubber bands exhibited fixity and recovery of 100% ± 10%. The recovery properties of the SMP were studied under various loading conditions and a model was fit to describe the potential recovery with relation to the fixation. An addition (open full item for complete abstract)

Committee: Kevin Cavicchi Dr. (Advisor); Robert Weiss Dr. (Advisor); Avraam Isayev Dr. (Committee Member); Coleen Pugh Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member) Subjects: Polymers

Master of Sciences, Case Western Reserve University, 2014, EMC - Mechanical Engineering

A modified dual-mode heat-flow meter method and a dynamic plane-source method are used to characterize the thermal conductivity of shape memory polymer composites with tunicate cellulose nanocrystals (CNC) fillers. The CNC fillers are shown to enhance the thermal conductivity of the composites by a factor of three to 0.31 W/m-K in the in-plane direction and by a factor of two to 0.23 W/m-K in the through-plane direction over the neat epoxy. These measurements imply that the thermal conductivity of the CNCs is on the order of 7.3 W/m-K as estimated by a simple composite thermal conductivity model. This investigation is a preliminary step towards future investigation of filler alignment driven thermal conductivity switching properties that may be exhibited by shape memory polymer composites.

Committee: Alexis Abramson (Advisor); Stuart Rowan (Committee Member); Joseph Prahl (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Nanoscience; Nanotechnology; Polymers

Master of Science in Engineering, Youngstown State University, 2013, Department of Mechanical, Industrial and Manufacturing Engineering

This work investigates the adaptive and morphing properties of SMCs based on a shape memory polymer (SMP) and a microvascular arrangement of shape memory alloys (SMAs). Here, the microvascular SMA phase has been subjected to a two-way shape memory effect (SME) process, in order to fully control the actuation properties of the SMC. It has been observed that the two-way trained SMA successfully induces a morphing performance on the SMC during a fluid heating-cooling cycle. The initial results suggest that the actuation behavior of the SMC strongly depends on the microvascular fluid heating rate as well as on the temperature difference between the glass transition temperature of the SMP and the activation temperature of the SMA. Analytical and Finite Element Method (FEM) analysis on the microvascular SMC has also been performed. The results suggest that the FEA analysis offers a better prediction of the thermo-mechanical behavior of the SMC. It has been observed that whilst the FEA successfully predicts the thermal profile of the SMC, the mechanical modeling seems to require a degree of amendment. Here, the FEA has predicted a deflection 20% higher than those experimentally recorded. Although a refinement is needed on the mechanical modeling of the FEA analysis, the current FEA work certainly provides the elementary design parameters for future optimizations of morphing structures based on SMC.

Committee: Pedro Cortes (Advisor); Hazel Marie (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Automotive Engineering; Automotive Materials; Chemical Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2013, Polymer Engineering

Shape memory behavior of a partially zinc-neutralized, poly(ethylene-co-methacrylic acid) ionomer (i.e. PEMA) was investigated. The ionomer was semicrystalline ionomer with a broad melting transition in the range 60-100 °C. Physical crosslinks in the ionomer due to an ionic nanodomain structure provided a “permanent” crosslinked network, while polyethylene crystallinity provided a temporary network. The broad melting transition allowed one to tune the dual-shape memory behavior by choosing a switching temperature, Tc, anywhere within the melting transition. Similarly, multiple shape memory behavior was achieved by choosing two or more switching temperatures within the melting transition, though the effectiveness of shape fixation depended on how much materials was melted and recrystallized to support the specific temporary shape. Crosslinking improved the recovery efficiency and the crosslinked ionomer exhibited nearly ideal shape memory behavior in dual-shape memory cycle. Preparation of blends of PEMA with ZnSt extended the range of temperatures in which shape memory properties can be achieved. A temporary shape was achieved and fixed by heating and deforming the sample above the melting points (Tm) of the crosslinked ionomer and ZnSt and then cooling the material below Tm under stress. The original shape was restored by reheating the sample above the Tm of the ionomer and ZnSt. Shape memory fibers were made from the blends of Zn-SEPDM ionomer and lauric acid. Zn-SEPDM is an elastomeric amorphous ionomer, the zinc salt of sulfonated poly{ethylene-r-propylene-r-(5-ethylidene-2-norbornene). Shape recovery was triggered by the melting of lauric acid crystals at temperatures close to body temperature, i.e. ~ 40 °¿. Shape memory polymer with such a triggering temperature may have application as self-tightening sutures for biomedical applications. Triple shape memory behavior was also achieved with the blend of Zn-SEPDM with lauric ac (open full item for complete abstract)

Committee: Robert Weiss Dr. (Advisor); Kevin Cavicchi Dr. (Committee Member); Sadhan Jana Dr. (Committee Member); Matthew Becker Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member) Subjects: Chemical Engineering; Engineering; Plastics; Polymers

Doctor of Philosophy, University of Akron, 2013, Polymer Engineering

This dissertation consists of two research subjects: High Temperature Shape Memory Polymers and Ionomer Modified Asphalts. Current development of thermally sensitive shape memory polymers (SMPs) has focused primarily on relatively low transition temperatures (Tc < 100°C) and elastomeric polymers, such as thermoplastic polyurethanes (TPU), crosslinked polyethylene, poly (e-caprolactone), sulfonated EPDM and polynorbornene. Those materials are appropriate for applications such as biomedical and surgical materials, smart fabrics and heat shrinkable tubing. Materials used as aerospace or structural components often require higher modulus and switching temperatures for shape change and actuation. To the best of our knowledge, there have been no reports of thermoplastic SMPs with controllable switching temperatures above 100°C. There has been research on high temperature SMPs but based on thermoset polymer systems. High temperature thermoplastic shape memory polymers were developed from metal salts of sulfonated PEEK (M-SPEEK, M=Na+, Zn2+, Ba2+, Al3+, Zr4+) ionomer and composites of the M-SPEEK ionomers with a fatty acid salt. M-SPEEKs were prepared by neutralizing sulfonated PEEK acid to metal salts. The glass transition temperatures of M-SPEEK ionomers increased with increasing Coulomb energy of ion pairs and the ionomers were thermally stable to ~320°C. The M-SPEEK ionomers exhibited microphase separated morphologies and the average correlation length was determined by small angle X-ray scattering. Al-SPEEK and Zr-SPEEK showed crosslinked characteristics such as rubbery plateau above Tg and much reduced water uptake. The M-SPEEK ionomers exhibited reasonable shape memory behavior, in which the permanent network was provided by ionic nanodomains formed by the interaction of ionic groups and glass transition temperatures served as the switching temperatures. The relative poor shape efficiency of Na-SPEEK and Zn-SPEEK (80-90%) can be improved by blendi (open full item for complete abstract)

Committee: Robert Weiss Dr. (Advisor); Kevin Cavicchi Dr. (Committee Chair); Jana Sadhan Dr. (Committee Member); Matthew Becker Dr. (Committee Member); Yi Pang Dr. (Committee Member) Subjects: Plastics; Polymer Chemistry; Polymers

Doctor of Philosophy, Case Western Reserve University, 2010, Macromolecular Science and Engineering

Main-chain liquid crystalline networks were prepared from mesogenic dienes using two different synthetic routes. First, main-chain liquid crystalline copolymers were synthesized by polymerizing a mesogen with a nonmesogenic comonomer using acyclic diene metathesis (ADMET) chemistry. The resulting polymers form nematic phases, with composition dictating the glass transition and isotropization temperatures. Free-radical crosslinking through the unsaturated bonds in the polymer was demonstrated for a selected composition to lead to an elastomeric network. This two step process was employed to control the polymer properties before crosslinking and serves as a viable route to tailored nematic networks for applications as anisotropic adhesives.Liquid crystalline elastomers (LCEs) were prepared using a second synthetic route that employed hydrosilylation chemistry to react the mesogens with hydride-terminated poly(dimethylsiloxane) and a vinyl crosslinker. The resulting LCEs formed a smectic-C phase with transition temperatures that depend on mesogen composition. The mesogens impart two distinct active behaviors to the elastomers. The first of these is actuation, the reversible extension and contraction of the polymer when cooled and heated, respectively, through the mesogen isotropization transition. Actuation is dependent on the crosslink density of the material and can cause the samples to elongate as much as 30 % under tensile load. The second active behavior is shape memory, the ability to fix a temporary deformation and later recover the equilibrium shape by heating. The LCEs have excellent shape memory fixing and recovery ratios, both of which generally exceeded 95 %. The ability of a soft network to fix strains above room temperature is unusual and was investigated using a combination of thermal analysis, mechanical testing, and wide angle x-ray scattering, where it was found that strain is fixed by freezing the mesogens within the smectic layers. The LCE's low mod (open full item for complete abstract)

Committee: Patrick Mather PhD (Advisor); Charles Rosenblatt PhD (Committee Member); Stuart Rowan PhD (Committee Member); Lei Zhu PhD (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 2010, Macromolecular Science and Engineering

Polyhedral oligosilsesquioxane (POSS)-based biodegradable polymers were investigated as stent coating for drug delivery from drug-eluting stents and as polymeric scaffold for fully bioabsorbable stents. A highly efficient and precise electrospraying technique, one of the electrostatic processing techniques, was developed for the stent coating application. The roughness of stent coatings produced was varied conveniently by the electrospraying technique utilizing different electrospraying mode or Coulombic fission, and was further modified using post-treatments of pure solvent electrospraying or vapor welding. Abluminal stent coatings were achieved utilizing the targeting nature of the charged electrospraying droplets to avoid luminal coating on stents by applying nonconductive materials temporarily contacting the inner surface of the stents.Long-standing questions of paclitaxel (PTx)-polymer blend miscibility and interactions were studied for particular polymer blends using characterization methods. It was found that paclitaxel is amorphous in all proportions in the blends of paclitaxel with POSS-based thermoplastic polyurethanes (POSS TPUs), and serves as an antiplasticizer by increasing the blend Tg gradually from the polymer Tg up to the substantially higher Tg of amorphous paclitaxel. The polyethylene glycol (PEG) segment incorporated in POSS TPUs exhibited specific hydrogen-bonding interactions with the paclitaxel and promoted the miscibility in the blends. Highly adjustable release of paclitaxel was achieved from both thermoplastic stent coatings utilizing P(DLLA-co-CL)-based POSS TPUs, and thermoset stent coatings employing PLGA-POSS end-linked thiol-ene network. Using a newly-developed drug release approximation model describing the entire drug release profile, paclitaxel release mechanisms from these biodegradable stent coatings were interpreted quantitatively, including the effects of polymer glass transition temperature, polymer initial molecular weight, (open full item for complete abstract)

Committee: Patrick T. Mather (Advisor); Gary E. Wnek (Committee Member); Lei Zhu (Committee Member); Horst A. von Recum (Committee Member) Subjects: Biomedical Research; Polymers