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

Plasma polymerization is a facile method of depositing robust films on a wide variety of substrates. While the nanoscale structure of films plasma polymerized in vacuum has been studied some, little is known of the nanoscale structure of the films deposited in the more complex atmospheric plasma polymerized (APP) films. To explore how deposition conditions affect APP film structures, APP films were deposited using hexamethyldisiloxane (HMDSO) precursor at varying power and in varying levels of relative humidity (RH). X-ray and neutron reflectivity measurements reveal that these APP-HMDSO films have a three-layer structure. A transition region of low mass density and carbon content forms next to the substrate as the deposition starts and etching by the plasma initially dominates deposition; a center region which still experiences some etching displays a uniform scattering length density (SLD) with respect to depth; a surface layer next to the air of mass density less than or equal to that of the center region forms whose SLD depends on how “filled in” the layer was when plasma generation was halted. Mass density was found to be sensitive to high humidity, which reduces the flux of monomer fragments to the substrate and allows them to pack more densely. Complementary analysis of depth-resolved X-ray photoelectron spectroscopy and water contact angle measurements show that composition and hydrophilicity are power-dependent. Films deposited at lower power lose more of their carbon to etching, making their composition more silica-like and making them more hydrophilic. Films deposited at higher power retain more of the carbon from the HMDSO monomer thanks to higher deposition rates; a film layer is buried by additional layers before all the residual carbon can be etched away. Neutron reflectivity measurements of the same APP-HMDSO films while exposing them to deuterated solvent vapor showed that vapor easily penetrated them without causing their thickness to increase, (open full item for complete abstract)

Committee: Mark Foster (Advisor); Mesfin Tsige (Committee Chair); Toshikazu Miyoshi (Committee Member); Ali Dhinojwala (Committee Member); Bi-min Newby (Committee Member) Subjects: Chemistry; Materials Science; Physics; Plasma Physics

Doctor of Philosophy, Case Western Reserve University, 2021, Biomedical Engineering

Post-surgical adhesions are internal scars that pathologically adhere together adjacent tissues/organs/biomaterials. They pose a tremendous but frequently underestimated burden across many surgical disciplines, being especially prevalent following abdominal surgery. Peritoneal adhesions can cause discomfort, intestinal obstructions, infertility, and increased morbidity/mortality of subsequent surgery. Once formed, treatments for adhesions tend to be risky and ineffective, so prophylactic strategies are desirable. Implantation of meshes, such as in hernia repair, often exacerbates peritoneal adhesions. Knitted polypropylene (PP) meshes are the most common hernioplasty devices, but are notoriously adhesiogenic owing to material and structural characteristics that promote incorporation, such as hydrophobicity and reticular construction. The ideal strategy to prevent mesh adhesions entails adhering a smooth, continuous, hydrophilic barrier material on the mesh visceral face to mitigate tissue attachment processes. Prior studies developed polymerized cyclodextrin (pCD) materials having unique capabilities for sustained, multi-window drug release, and suggested that these hydrophilic polymers passively resist cell attachment. In several animal species, pCD could deliver antibiotics for weeks to successfully resolve mesh infection, another hernioplasty complication for which only suboptimal solutions exist. In the present work, pCD materials were explored toward application as novel adhesion barriers for PP surgical meshes. First, nonthermal plasma activation was assessed as a strategy to improve PP-pCD bonding, as PP is generally unreceptive to coatings. Plasma introduced hydroxyls onto PP, enhancing PP-pCD adherence. Second, protein adsorption, bacterial attachment, and fibroblast viability/attachment upon pCD-coated and bare PP materials were evaluated. These events play roles in mesh adhesion, infection, and biocompatibility. pCD decreased protein adsorption and bacter (open full item for complete abstract)

Committee: Horst von Recum PhD (Advisor); Jeffrey Capadona PhD (Committee Chair); Kathleen Derwin PhD (Committee Member); Guang Zhou PhD (Committee Member); Michael Rosen MD (Committee Member) Subjects: Biomedical Engineering

Doctor of Philosophy (PhD), Wright State University, 2005, Engineering PhD

Pulikollu, Rajasekhar Venkata. Ph.D., Department of Mechanical and Materials Engineering, Wright State University, 2005. Nano-coatings on Carbon Structures for Interfacial Modification. Surface modification of materials is a rapidly growing field as structures become smaller, more integrated and complex. It opens up the possibility of combining the optimum bulk properties of a material with optimized surface properties such as enhanced bonding, corrosion resistance, reactivity, stress transfer, and thermal, optical or electrical behavior. Therefore, surface functionalization or modification can be an enabling step in a wide variety of modern applications. In this dissertation several surface modification approaches on carbon foam and carbon nano-fibers will be discussed. These are recently developed sp 2 graphitic carbon based structures that have significant potential in aerospace, automotive and thermal applications. Influence of surface modification on composite formation and properties have also been investigated. Two types of property changes have been investigated: one for enhancing the surface reactivity and another for surface inertness. Characterization techniques such as X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Contact Angle Measurement, Scanning Electron Microscope (SEM), Transmission Electron Microscope(TEM), and mechanical testing are used in this study to find out the influence of these coatings on surface composition, chemistry, and morphology. Mechanical testing has been performed on composites and stand-alone foam to study the influence of surface modification on physical and mechanical properties of the composite materials. The effectiveness of these coatings on metallic/graphite interface has also been investigated for metal-matrix composite related applications. Additionally, the influence of plasmacoatings on nucleation and growth of nanotubes on larger carbon structures (to produce multiscale, multifunctional mater (open full item for complete abstract)

Committee: Sharmila Mukhopadhyay (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2001, Engineering : Materials Science

Plasma polymerization was investigated as a potential method of producing optical devices. Two different types of optical devices were considered: dye-doped silicon based optical stacks and organic thin film interference filters. The effectiveness of plasma polymerized HMDS barrier layers to stop interlayer chromophore diffusion and produce temporally stable devices was evaluated. The thickness of the barrier layer and the molecular architecture of the substrate were both found to play a role in the diffusion limiting properties of the plasma polymerized barrier layer. Plasma polymerization allows for the deposition of films with a wide variety of physical and chemical properties, including thin, dense, crosslinked films. The use of plasma polymerization is a viable means of limiting chromophore diffusion in optical stacks to create devices employing non-homogeneous device concentrations with temporal stability. Plasma polymerization was investigated as a means of constructing organic anti-reflection (AR) coatings, organic quarter-wave (QW) stacks and organic rugate filters. To date, virtually all materials used for optical films are inorganics. In fact only inorganic materials can be deposited to create films with a controlled, periodic and continuous variation in refractive index. As a result, all rugate filters to date have been fabricated from inorganics, even though optical components are commonly constructed of both organic and inorganic materials. Differences in surface energy and thermal expansion coefficients between organic substrates and inorganic coatings lead to problems such as delamination. This incompatibility has given rise to a desire to produce inhomogeneous organic coatings. The possible use of plasma polymerized benzene (PP-benzene) and plasma polymerized Octafluorocyclobutane (C4F8) (PP-OFCB) as organic AR coatings and organic QW stacks was evaluated. The refractive indexes of PP-benzene and PP-OFCB were determined as 1.63 and 1.39 respectively (open full item for complete abstract)

Committee: Dr. Stephen J. Clarson (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, Case Western Reserve University, 2010, Chemical Engineering

Patterning processes combined metal masking and selective diamond growth to fabricate conductive diamond patterns on various substrates, allowing either the growth or nucleation surfaces to be applied as electrodes. These processes enable novel applications of diamond electrodes integrating diamond films into existing sensor systems and novel, temperature intolerant, polymer-based systems. A patterning process was initially developed for thermally oxidized silicon. Two nucleation (BEN and sonication seeding) and two growth (HFCVD and MPCVD) methods were evaluated. Feature dimensions and spacing down to 8 μm were obtained, having a minimal thickness of 1 μm. The films were high-quality polycrystalline diamond, as analyzed by Raman spectroscopy. As electrochemical sensors, the films detected dopamine (10 μM in PBS) with redox properties typical of microcrystalline diamond. Attempts using BEN to selectively deposit diamond on insulating surfaces (alumina, high-temperature borosilicate glass) required metal coating of the back and sides of substrates. With alumina, adhesion problems prevented growth of complete films (or patterns). With glass, interactions between the tungsten and substrate prevented etching of the mask, compromising the pattern. Patterns on silicon dioxide were transferred to a polynorbornene polymer support with metal (Au, or Cr/Au/Cr) contacts to create the first diamond-on-polymer sensors - making the smooth, diamond nucleation surface the active electrode surface. The patterning process was scaled from ¼” chips to 3” wafers, to fabricate multi-electrode arrays (10 singly addressable pads). Sonication seeding was used to seed wafer-scale substrates due to limitations in implementing BEN with larger scale substrates. As-fabricated, diamond-on-polymer electrodes from the wafer-scale process showed a highly capacitive dielectric response. XPS depth profiling revealed a SiOxCy layer on the electrode (diamond nucleation) surface, an issue introduced by t (open full item for complete abstract)

Committee: Heidi B. Martin PhD (Committee Chair); R. Mohan Sankaran PhD (Committee Member); C. C. Liu PhD (Committee Member); Christian A. Zorman PhD (Committee Member) Subjects: Chemical Engineering