Thesis (Ph. D.)--Ohio State University, 1973. / Includes bibliographical references (leaves 137-140). Available online via OhioLINK's ETD Center

Diblock copolymers are a class of polymers where two dissimilar polymer blocks are joined together at a common end. The dissimilarity of the blocks causes a phase separation to take place, however the connectivity of the blocks keeps the length scale of this phase separation on the order of the radius of gyration of each of the blocks. Throughout this thesis, the synthesis and morphology of diblock copolymers that have a specific, UV cleavable chemical moiety located at the junction point between the two blocks is investigated. The two junction points targeted to this end are the [4π + 4π] photodimer of anthracene and the 2-nitrobenzyl ester. The diblock copolymer containing the [4π + 4π] photodimer of anthracene exhibits thermal as well as UV lability upon heating above ∼130°C, or UV irradiation at 280 nm. Thin films of this polymer on neutrally-interacting substrates were annealed at 80°C under the presence of supercritical carbon dioxide to avoid thermal degradation that would occur if films were annealed above the glass transition temperature of both blocks (>110°C). The transition from microphase-separated to macrophase-separated morphology is thoroughly investigated by AFM upon thermal and UV cleavage to create blends of diblock and homopolymer in situ. In addition, the selective removal of each polymer block after cleavage by washing with selective solvents is demonstrated. The diblock copolymer containing the 2-nirobenzyl ester moiety is also synthesized and its morphology in thin films is investigated. This diblock, upon cleavage, leaves behind more useful functionality than the diblock with the [4π + 4π] photodimer of anthracene as junction point, as well as being thermally stable at temperatures that allows thermal annealing of thin films. The UV cleavage characteristics of this copolymer in solution are investigated by SEC. Also, irradiation of thin films at a wavelength that does not degrade or cross-link either polymer block causes selective junction point cleavage, as expected. The morphology of UV cleaved thin films on neutrally-interacting substrates is investigated by AFM.

The overall goals of this research were to establish better selection criteria for the use of polymeric coatings and to develop unique material characterization techniques to measure the properties of thin polymer films. The main focus was on establishing structure/processing/property relationships for novel anisotropic polyimide coatings and measuring their in-plane and out-of-plane properties. This involved understanding the effect of processing conditions on the state of stress and on the material properties, and determining the anisotropic elastic constants. The materials investigated were a variety of polyimides, including some novel fluorinated polyimides. Extensive processing and testing of these materials has been carried out. Residual and thermal stresses have been measured using the technique of vibrational holographic interferometry. The stresses have also been measured under different temperature, humidity, and processing conditions. These polymers are very anisotropic with widely different in-plane and out-of-plane properties. The primary goal of this research was the determination of anisotropic elastic constants--tensile moduli, shear moduli and Poisson's ratios--to aid in reliable modeling of polymers in actual applications. All these constants have been determined using existing as well as new unique techniques. The structure/processing/property relationships for these materials have also been investigated. The anisotropy in properties results from a preferred in-plane orientation in polyimides. The effect of polymer structure, film thickness, and processing conditions on the orientation, and hence on the material properties, has been studied. The material properties have been evaluated by physical, mechanical, and thermal testing. The orientation has been characterized by wide angle x-ray diffraction (WAXD) and birefringence measurements. Another important aspect of reliability of polymeric coatings is the adhesion between coating and substrate. The adhesion of these polyimides to a silicon wafer substrate has been evaluated by a self-delamination method. The improvement in adhesion strength of the polyimide-silicon interface by using a silane coupling reagent has been studied.

Thesis (M.Ch.E.)--University of Delaware, 2006. / Principal faculty advisor: Annette D.Shine, Dept. of Chemical Engineering. Includes bibliographical references.

In this dissertation, new ways for controlling the internal structures of a system of polymer composites, polymer blends, and hydrogel composites by means of external electric or magnetic fields are presented. The first part of this study addresses the development of an anisotropic phase-separated morphology in polymer blends by using electrically pre-oriented clay particles. It was observed that electrically pre-oriented montmorillonite clay particles in a homogenous single-phase blend lead to anisotropic phase-separated morphology of the blends, undergoing demixing upon temperature shift to a two-phase regime. The initial co-continuous microstructure developed into a coarsened and directionally organized phase-separated morphology parallel to the direction of oriented clay particles (applied AC electric field direction) over the annealing time. It was also found that the degree of clay orientation under AC electric field was linearly proportional to the degree of polymer-phase orientation. The temporal morphological evolution was thoroughly analyzed by electron microscopy and X-ray diffraction studies. The second part of the study covers anisotropic hydrogel nanocomposites developed by orienting magnetically sensitive nontronite clay minerals under the strong magnetic fields. Anisotropic hydrogel nanocomposites were formed by magnetic-field assisted orientation of nontronite clays suspended in a hydrogel precursor solution followed by a gelation process. The degree of orientation of nontronite minerals was quantitively characterized by birefringence and small-angle X-ray scattering. The resultant hydrogels exhibited anisotropic optical, mechanical, and swelling properties along the direction of oriented clay minerals. Anisotropic water swelling behaviors can be particularly applied in medical dressing materials, where vertical wicking of fluid into the wound dressing is sought after for minimizing periwound maceration damage.

<p>    </p> <p>To meet the needs of the high-end electronics and energy industry, it is important to operate these devices in elevated temperatures and under high voltage. The dielectric materials for advanced capacitors must have high temperature tolerance (Tg>80C) high dielectric constant, low loss and high breakdown strength to meet the demands of the future. In order to understand fundamental relationships between the processing, structural hierarchy and electrical properties, in this dissertation we focus on slow crystallizing PET/PEI polymer blends, crystallizable Nylon 12 and noncrystallizable Polyetherimide and its chemical variants. </p>

<p>The interface between two dissimilar materials often presents a challenge for materials engineers. Mismatches of moduli, coefficients of thermal expansion, surface energies and chemical functionalities can create headaches for engineers seeking to control and understand interfacial bonding. In this work, I am interested in two specific interfacial problems: the adhesion of pressure sensitive adhesive tapes to various substrates and the interface in polymer reinforced composite materials between the reinforcement phase and the matrix.</p> <p>Pressure sensitive adhesive tapes (PSATs) are an important class of materials with applications ranging from medical adhesives to roadway markings. In this work, I present a novel 90° peel fixture to be used in the evaluation of road tapes on roadway surfaces in construction zones. This modular fixture was validated on control surfaces before demonstrating the capability to test pavement marking tapes from road surfaces. Within the context of medical adhesives, I am interested in the deformation of the skin around the PSAT during peeling. By developing a model to predict this deformation, adhesives can be tailored to mitigate skin damage. I present experimental evidence indicating the independence of peeling force to the elastic modulus of the substrate along with deformation measurements of skin analogs during the removal of a medical tape. A new model for predicting the deformation of soft substrates during peel is reported based on the contact mechanics of a rectangular prism indenting an elastic half space.</p> <p>Polymer matrix composites are another category of materials which are increasingly adopted to improve performance or efficiency by reducing the weight of components. These materials offer a high specific strength but often fail catastrophically rather than gradually. Using stress responsive fluorescent molecules called mechanophores, I present a methodology to quantify stresses within the polymeric matrix near the reinforcement phase. By correlating in situ fluorescence intensity measurements during a uniaxial tensile test to stresses predicted from a finite element analysis model, a calibration was developed. This calibration was then applied to increasingly complex composite geometries. Chemically bonding these mechanophores to the interface between two materials allows for the detection of interfacial failures through fluorescence microscopy. I present a technique to synthesize interfacial spirolactam mechanophores on industrially relevant epoxy and silica material systems. I demonstrate the ability of these systems to detect failures in the system through in situ confocal microscopy during deformation.</p>

<p dir="ltr">Efficiently identifying commercial and improvised explosives is a crucial prerequisite for disarming and disposing of these dangerous materials. In conjunction with traditional techniques (e.g., ion mobility spectrometry and mass spectrometry), electrochemical sensors can function as low-form factor and inexpensive options to quickly identify chemical threats. In particular, organic electrochemical transistors (OECTs) have many attractive properties, and they have become viable options for biosensing. OECTs employ a simple geometry consisting of a conducting polymer active layer and an electrolyte controlled by a gate electrode. In turn, this provides a means for the solution-phase detection in short times. Here, the OECT architecture was extended to the challenge of explosive trace detection. These sensors were adapted to detect several families of explosives (i.e., acid-salts, nitroaromatics, nitroamines, nitrate-esters, and peroxides). Many of these sensors incorporated molecularly imprinted polymers (MIPs) to improve chemical selectivity. These MIPs were shown to introduce size exclusive properties to the OECTs, which can be leveraged to detect acid salts explosives. MIPs that were complementary to nitrated explosives (nitroaromatics, nitroamines, and nitrate-esters) also were prepared. These MIPs can adsorb their respective explosive decreasing their polymer porosity and ion-transport. Finally, a stand-alone OECT design was applied to detect peroxide-based explosives. These explosives were decomposed to hydrogen peroxide intermediates. The evolved hydrogen peroxide was then identified as it was electro-oxidized at the gate electrode. After establishing the viability of the discussed techniques, two new directions for designing OECT sensors were proposed. Finally, these two outlooks were combined as a potential strategy for directly detecting peroxide-based explosives. While only a small subset of explosives was considered, the strategies applied were not unique to these specific targets. Indeed, these OECTs detecting principles could be applied to a broader scope of explosives detection as well as novel chemical sensing horizons.</p>

Many sticky denizens of the ocean use unique and effective techniques to stick together and adhere to surfaces underwater. Underwater adhesion is a daunting task that many have set out to solve. One of the key factors of underwater adhesion and focus of this dissertation will be on negative charges and their role in underwater adhesion. Following previous work done on poly[(3,4-dihydroxystyrene)-co-styrene], an adhesive mimic to mussel adhesives, new functional groups were introduced to the same backbone to determine the change in adhesion in underwater and dry conditions. These functional groups were mainly comprised of negatively charged moieties such as sulfonates, phosphates, and phosphonates. Phosphates have been shown to exist in mussel proteins alongside positively charged proteins. A main facet of this dissertation will be focused on the specific synthesis pathways of modified charged synthetic mimics of existing polymer systems both styrene and acrylic based. Synthetic pathways were a challenging aspect of designing these polymers as functionalization can add many steps to the synthesis of polymers which makes the process tedious and lengthy. Characterization of these polymers were also important for determining the successful synthesis of these functionalized polymers. Several reactions conducted from this research have not been used on polymeric species and have been shown primarily in small organic molecules. Early work on poly[(3,4-dihydroxystyrene)-co-styrene]-based sulfonates, phosphates, and phosphonates established a foundation in pre and post functionalization of polymer species. Testing of adhesion, exploration of functionalization and synthesis optimization were the main goals for each type of functionalized polymer. Following the tests of many poly[(3,4-dihydroxystyrene)-co-styrene] based functionalized polymers it was shown that acrylic versions of phosphates performed substantially better for both 16 dry and underwater adhesion, especially on SAE 304 stainless steel. The acrylic phosphate polymers were based on previous DMA/MMA polymer systems that have shown to have excellent adhesive potential. The phosphate monomer MAEP was introduced to the polymer structure, which facilitated increased binding to steel substrates. Despite the acrylics overwhelmingly higher adhesion compared to the functionalized poly[(3,4-dihydroxystyrene)-co-styrene] polymers the phosphonate versions were shown to form a coacervate like material with positive charged poly[(3,4-dihydroxystyrene)-co-styrene] mimics. These “coacervates” had appreciable adhesion, much higher than the negative or positive versions had alone in dry conditions but despite this could not retain their metastable coacervate phase in wet conditions. Further study is underway in determining the role of negative charges in varying systems and determining whether adding negative charge to a polymer system truly helps with underwater adhesion alone.

<div>For over 20 years, biaxially oriented polypropylene (BOPP) has been used in capacitors as the dielectric material. BOPP has very high breakdown strength, low electric loss, and is relatively inexpensive however, it suffers from low dielectric constant and low usage temperature. The ever growing technology market requires more robust capacitors which can be used in high temperature and pulsed power applications, and the aim of this research is to meet or exceed dielectric properties of BOPP by combining specific polymer materials in layered structures, biaxially orienting the films, and heat setting the films to further improve thermal stability. Post-processing is done on custom built machines which track real-time true stress, true strain and birefringence values, allowing for a more complete picture of mechano-optical properties generated during the stretching process. These data, along with offline characterization techniques such as X-ray scattering and DSC, were coupled with dielectric property testing to help form relationships between polymer processing, morphology, and dielectric properties.</div><div><br></div><div>In Chapter 3, microlayer PET and PVDF (50:50 ratio) films with 32 total layers and thickness around 125 micron were provided by PolymerPlus. Films were first stretched uniaxially at varying temperatures in order to optimize processing conditions. Characterization confirmed PVDF crystal form transformation from alpha to beta form when films were stretched at 95^oC, and presence of - PVDF when stretched in molten state at 185^oC, sandwiched between solid PET layers. Dielectric properties were tested for films stretched at 150^oC, which exhibited low dielectric constant when PVDF spherulites or smaller, broken up fibrils were present, but improved dielectric constant when PVDF morphology consisted of long, highly ordered fibrils. Uniaxial drawing helped lower dielectric loss, and it further signicantly decreased at very high strains. In this case, morphology of uniaxially drawn PET did not have a strong correlation with dielectric constant, but higher PET crystallinity and orientation likely helps to lower dielectric losses.</div><div><br></div><div>Polymer microlayer fims consisting of 32 layers, 50:50 ratio PET to PVDF films were also studied extensively using thermal heat setting technique. Samples with good thickness uniformity after stretching were selected for these experiments, and offline characterization techniques were applied to study morphology. Films were annealed at temperatures around PVDF melting peak, which caused transformation of PVDF polymorphs from primarily alpha to combined gamma and/or gamma' forms. When oriented at 150^oC to 1.5X1, and ' -PVDF were detected in small amounts (via DSC) after annealing at 172^oC, and only ' after higher temperature annealing. Stretching at 150^oC to higher strains produced high amounts of '-PVDF only when annealed at 155^oC for films stretched to 3.5X1, and annealed at 150^oC for films stretched to 2.5X1. Offline characterization led to development of a structural model for PVDF layers alone, by de-laminating film layers. Then, morphology was correlated with dielectric properties by testing lms at room temperature, and at constant frequency, in temperature ramping experiments. Temperature ramping dielectric experiments showed that high percent crystallinity of PET may also help improve loss behavior at high temperatures. Furthermore, samples containing gamma and/or gamma'-PVDF had increasing dielectric constant with increasing temperature, however dielectric loss also greatly increased with increasing temperature. A significant conclusion was that the annealed sample without gamma or gamma'-PVDF present had only a slightly lower dielectric constant at high temperature testing, but also had much lower loss, making it a potential candidate for high temperature capacitor applications.</div><div><br></div><div>Other materials for potential dielectric film applications were studied as well. Two fluoropolymer films consisting of monolayers of ETFE and THV were uniaxially oriented and their morphology was characterized offline to elucidate structure-process-property relationships. Film samples produced were not large enough to be tested for dielectric properties, however morphology development during uniaxial orientation was evaluated. Both films showed nearly affine stretching behavior, and mechano-optical properties were studied during stretching at several temperatures. Combinations of X-ray scattering experiments and AFM led to proposed morphological structure models for each material at varying levels of deformation.</div><div><br></div><div>Finally, in collaboration with A. Schulman, Inc., PET and EVOH compounded blend and three layer PET-EVOH-PET films were oriented uniaxially and the morphology of the two was compared to each other. Potential applications include high barrier food packaging applications, due to the very high oxygen barrier but poor water vapor barrier of EVOH, which can be complimented by PET's high water vapor barrier. Uniaxial orientation of these two film systems showed that mechano-optical behavior was significantly different for blend versus layered films. Crystalline orientation factors were calculated from 1D WAXS data, which showed PET orientation was largely unaffected by increasing EVOH content in blend films, but blending decreased orientation of EVOH. PET's orientation in layered films was also largely unaffected by amount of EVOH in inner layer. EVOH's orientation factor was higher in all layered film compositions compared to neat EVOH film after stretching, suggesting that the coextrusion process is beneficial to increasing orientation of EVOH.</div><div><br></div>