Various techniques of fabricating surface patterns of small scales have been widely studied due to the potential applications of surface patterns in a variety of areas. It is a challenge to fabricate well-ordered surface area efficiently and economically. Evaporation-induced surface patterning is a promising approach to fabricate well-ordered surface patterns over a large area at low cost. In this study, the evaporation-induced surface patterns with controllable geometrical characteristics have been constructed. The dewetting kinetics on deformable substrate is also investigated. Using simple templates to control the geometry and the evaporation behavior of a droplet of volatile solvent, various gradient surface patterns, such as concentric rings, multiple straight stripes formed with a straight copper wire, etc. have been constructed on PMMA films. The wavelength and amplitude are found to decreases with the decrease of the distance to the objects used in templates. There is also a nearly linear relation between the amplitude and wavelength. The effects of several experimental parameters on the geometrical characteristics of the surface structures are studied, i.e. dimensions of the template, film thickness (solution concentration), substrate temperature, etc. The wavelength and amplitude increase with the increase of the film thickness (solution concentration), with the increase of the dimension of the template. However with the increase of the substrate temperature, the wavelength increases, while the amplitude decrease. Hexagonal network in pre-cast PMMA film have been fabricated by a “breath figure” approach at low humidity and low substrate temperature. The dimensions of the hexagonal holes are dependent on the template size and film thickness. The kinetics of the evaporative dewetting of a liquid (toluene) film on a deformable substrate (PMMA film) with the confinement of a circular copper ring is also studied. The liquid film first dewets from the outside towards the copper ring. When a critical volume is reached, an internal contact line appears, which dewets from the center to the copper ring smoothly with a constant velocity, then switches to a “stick-slip” motion. The average velocity of the smooth motion increases with the increase of the copper ring size and film thickness.

Density Functional Theory (DFT) and time-dependent Density Functional Theory (TD-DFT) are powerful tools for modeling orbital energy in conjugated molecules and have been useful tools for research in organic photovoltaics. In this work, DFT is first used to explain the red shift in the absorption spectrum and increased absorption observed in MEH-PPV. Initially, the modeling of the red-shift in the absorption peak of MEH-PPV is studied using Gaussian 03 software with the global hybrid functional B3LYP for exchange-correlation and the 6-31G basis set. DFT and TD-DFT are used to separately study the effects of polymer chain length, carbon-carbon double-bond stretching, and the polymer in solution vs. in gas space on red shift in absorption spectrum. Next, Gaussian 09 software and the same B3LYP functional and 6-31G basis set are used to study interchain and intrachain interactions of MEH-PPV in solution. The red shift in the absorption peaks for three MEH-PPV configurations (single-chain pentamer, two stacked pentamers, and decamer) are compared with experimental results for five different solvents (chloroform, toluene, xylene, dichloromethane, and chlorobenzene). This investigation indicates that inter-chain interactions dominate in “good” aromatic solvents as compared to “poor” non-aromatic solvents. The results suggest that inter-chain charge transfer interactions play a critical role in real solutions and inter-chain aggregation takes precedence over intra-chain aggregation in aromatic solvents. In the final section of the study, accurate values for the range-separation parameter (w) for three lengths of MEH-PPV polymer (trimer, tetramer, and pentamer) in five different solvents (chloroform, chlorobenzene, xylene, Tetrahydrofuran, and dichloromethane) are reported using the range-separated functionals wB97XD and CAM-B3LYP. Using these data, range separation parameters are predicted and used for longer polymer chains in chloroform solution. The differences in the range separation parameters for the different solvents is statistically significant and gives further insight into the polymer/solvent interaction.

Metal-organic frameworks (MOFs) have been extensively studied because of their amazing applications in gas storage, purification, photocatalysis, chemical sensing, and imaging techniques. Ruthenium polypyridyl complexes have been broadly considered as photosensitizers for the conversion of solar energy and photoelectronic materials. With this aspect, we have synthesized three new ruthenium polypyridyl based MOFs ([Ru(H2bpc)Cu(bpc)(Hbpc)2(H2O)]·5H2O (1), [Ru(H2bpc)(Fe(bpc)(Hbpc)2(H2O)2]·6H2O (2) and [Ru(H2bpc)Ni(bpc)(Hbpc)2(H2O)2]·6H2O (3)) from ruthenium(III) chloride, bpc (2,2’- bipyridine-4,4’-dicarboxylic acid) ligand, and 3d M(II) metal ions (M(II)= Cu(II), Fe(II), Ni(II)). These MOFs were synthesized under hydro or solvothermal conditions by using water, ethanol or methanol as solvents. The crystal structures of the new compounds contains zigzag chains of [Ru(bpc)3]n- complex ions linked by Cu, Fe or Ni complex ions individually. Above synthesized crystal structures were characterizing by single-crystal Xray and powder X-ray diffraction strategies, UV-vis and IR spectroscopy. Thermal properties were determining by thermogravimetric analysis. Magnetic properties were also studied.

Stimuli-responsive materials are changing the landscape of actuated materials, optoelectronics, molecular machines, solar cells, temporary memory storage, and biomedical materials. Specifically, photo-responsive polymers have gained acceleration in research and application since the last two decades in the form of a surface coating and micro-patterns. Light as a stimulus can be coherent, mono or polychromatic, tunable for power (intensity) and energy (wavelength), and has precise spatiotemporal control. Conventional surface coating techniques such as spin coating are unable to impart properties to the coatings in terms of sturdiness, homogeneity, uniformity over the complex surface, post deposition modification, and process efficiency. Also, in the field of photoreponsive polymers, there is no simple technique for surface-patterning of photo-responsive polymers, which is an important missing link between current research and future potential applications. This dissertation designs new strategies for light-mediated ring opening metathesis polymerization (ROMP) to synthesize a diverse class of stable photo-responsive polymers and coatings. Firstly, we propose a new synthetic route to functionalize surface-initiated ring opening metathesis polymerization (SI ROMP) coatings. The backbone of ROMP polymers has internal carbon-carbon double bonds which are potential sites to introduce additional functionalities like stimuli-responsive functional groups. We leverage these unsaturated bonds to incorporate functionalized side chains using thiol-ene click chemistry. Thiol-ene chemistry is a versatile approach to attach diverse functional groups at the site of a carbon-carbon double bond. This approach was tested by grafting 3 types of thiols with different functional tail groups and can be readily used for any polyolefin coatings. Secondly, oxidative degradation of SI ROMP coatings in the organic solvent is a common problem resulting in a decrease in the film thickness due to polymer chain cleavage. We incorporated a custom designed crosslinker to the polynorbornene (pNB) coatings to prepare in situ crosslinked pNB coatings. This approach provides a crosslinked coating of pNB with significantly increased stability against organic solvents by decreasing the film loss from 73 % to 28 %. Lastly, a novel approach of making photo-responsive polymer by light mediated ROMP is demonstrated. Light mediated control over rate of polymerization is the key feature required for patterning surface with photoresponsive polymers. We achieved this goal by designing and synthesizing a monomer that effectively controls the activity of the catalyst by temporarily deactivating it on irradiation with UV 365 nm light and reactivating it back by irradiation with blue 455 nm light to resume the ROMP.

Mixed matrix membranes (MMM) offer one potential path toward exceeding the Robeson upper bound of selectivity versus permeability for gas separation performance while maintaining the benefits of solution processing. Many inorganic materials, such as zeolites, metal-organic frameworks, or carbon nanotubes, can function as molecular sieves, but as stand-alone membranes are brittle and difficult to manufacture. Incorporating them into a more robust polymeric membrane matrix has the potential to mitigate this issue. In this work, phase inversion polymer solution processing for the fabrication and testing of asymmetric flat sheet mixed matrix membranes was employed with CVD-derived multiwall carbon nanotubes (MWCNTs) dispersed in a polyethersulfone (PES) matrix. The effect of MWCNT loading on membrane separation performance was examined. Notably, a distinct enhancement in selectivity was measured for several gas pairs (including O2/N2) at relatively low MWCNT loading, with a peak in selectivity observed at 0.1 wt% loading relative to PES. In addition, no post-treatment (e.g. PDMS caulking) was required to achieve selectivity in these membranes. In contrast, neat PES membranes and those containing greater than 0.5 wt.% MWCNT showed gas selectivity characteristic of Knudsen diffusion through pinhole defects. These results suggested that at low loading, the presence of MWCNTs suppressed the formation of surface defects in the selective layer in flat sheet mixed matrix membranes. Additionally, a bench-scale, single-filament hollow fiber membrane spinning line was designed and purpose-built at the University of Kentucky Center for Applied Energy Research (CAER). Hollow fiber membrane spinning capability was developed using polyethersulfone (PES) solution dopes, and the process was expanded to include polysulfone (PSf) as well as mixed matrix membranes. The effects of key processing parameters, including the ratio of bore to dope velocities, the spinning air gap length, and the draw-down ratio, were systematically investigated. Finally, direct hollow fiber analogues to flat sheet mixed matrix membranes were characterized. Consistent with the flat sheet experiments, the mixed matrix hollow fiber membranes showed a local maximum in selectivity at a nominal loading of 0.1 wt.% MWCNT relative to the polymer, suggesting that the pinhole suppression effect introduced by MWCNTs was not limited to flat sheet membrane casting. The development of asymmetric hollow fiber mixed matrix membrane processing and testing capability at the UK Center for Applied Energy Research provides a platform for the further development of gas separation membranes. Using the tools developed through this work, it is possible to further push the frontiers of mixed matrix gas separation by expanding the capability to include more polymers, inorganic fillers, and post treatment processes which previously have been focused primarily on the flat sheet membrane geometry.

Ice buildup on structures leads to problems that include reduced performance, structural damage and power outages. It is therefore important to limit the energy required for removal of ice from substrates to minimize buildup. Understanding the mechanism of ice adhesion and its dependence on variables like coating thickness, stiffness, surface free energy and morphology is critical for minimizing adhesion. Despite several developments in “icephobic” coatings, which are those that have low ice adhesion, it is important to understand adhesion on the fundamental level to make way for advanced coatings. To do so, a study has been carried out that explores key variables affecting ice adhesion using a commercially available silicone, Sylgard 184®. Sylgard 184 is a two-part, platinum cured silicone elastomer available from Dow Corning with good physical and chemical stability and is used in widely diverse research studies. The thermodynamic work of ice adhesion is related to the receding contact angle θ_r of water by Equation 1. wa≈ γ_w (1+cos⁡ θ_r) Eq 1. where γ_w is the surface tension of water. Considering an elastomeric substrate and ice as a rigid cylindrical adherent, the Kendall modelcan be adapted to relate peak removal force (Pc) with work of adhesion (wa), modulus (K), thickness (t), and radius (a) according to Equation 2. Pc ∝ πa^2 ((2wa K)/t)^(1⁄2) Eq. 2 Considering these relationships, hydrophobic materials with low surface energies and high receding contact angles are generally predicted to show low adhesion. To begin to understand details, the force required to remove an ice cylinder from the silicone elastomer Sylgard 184 was investigated by focusing on three variables: coating thickness, modulus and cure temperature. “Cure” refers to the network formation or crosslinking within the material. The Wynne research group has previously established a surprising dependence of qR on Sylgard 184 cure temperature.In this thesis, the relationship among variables noted above was examined by measuring Pc for Sylgard coatings. Additionally, effects of test temperature on ice adhesion strength was studied. Surface characterization methods including ATR-IR (attenuated total reflectance infrared spectroscopy), DCA (Wilhelmy plate dynamic contact angles) and AFM (atomic force microscopy) were employed. In summary, defined processing conditions were found optimum for minimizing ice adhesion to Sylgard coatings.

Numerous publications are available on the structure and properties correlation of fibers spun from polymers with flexible chains such as polyethylene terephthalate (PET), nylon, polypropylene. Also considerable amount of work is reported in fibers spun from rigid rod polymers like poly(p-phenylene terephthalamide) due to their value in high performance fibers category. However, very limited literature is available on the structure-properties relationship in fibers manufactured from poly(phenylene sulfide) (PPS), a high performance polymer which possesses chain flexibility between above two classes of polymers. A few researchers have studied crystallization kinetics and the fibers by extruding the polymer using capillary rheometers. However, there is a lack of in-depth study of conversion of PPS into fibers through melt spinning and further enhancement of properties by drawing and annealing experiments. The purpose of the present research was to fill this void by systematically studying the fiber manufacture from PPS polymers. Four variances of proprietary Fortron® linear PPS resins differing in MW were analyzed for their characteristics such as molecular weight (MW) and MW distribution (MWD) using gel permeation chromatography (GPC), rheological properties using melt flow indexer (MFI) and capillary extrusion rheometer, and crystallization kinetics using differential scanning calorimetry (DSC). The fibers were spun on a pilot melt spinning facility, using a multi-hole spinneret, under different processing conditions. As-spun fibers were drawn and annealed subsequently by varying draw-annealing conditions. Thorough characterization of the as-spun and drawn-annealed fibers was carried out using various analytical techniques such as tensile testing, DSC, polarized light optical microscopy (POM), wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). Relationship between polymer characteristics, process conditions and structure-properties in the fibers was analysed statistically. A strong correlationship between polymer molecular weight, processing conditions during melt spinning and draw-annealing, processing behavior during melt spinning and drawing, fiber tensile properties and fiber morphology is reported herein. Interaction effects of material and process variables in evolving fiber structure and properties are also discussed. Through optimal combination of material and process variables, PPS fibers of tenacity close to six gpd were obtained. With the help of several characterization tools listed earlier, melting behavior of PPS polymers and fibers is decoded, and probable structural model of high tenacity PPS fibers is proposed.

This dissertation presents material design strategies to investigate cell-biomaterial interactions on specific biocompatible polymers and polymer blends by using mouse pre-osteoblastic MC3T3 cells aiming for potential applications in bone tissue engineering. Chapter 1 reviews some related background knowledge including polymeric biomaterials for tissue engineering, cell-biomaterial interaction, synthetic photo-crosslinkable and degradable polymers, and the effect of surface features on osteoblast cell responses. Chapter 2 presents photo-crosslinkable composites of poly(propylene fumarate) (PPF), an injectable and biodegradable polyester, and methacryl-polyhedral oligomeric silsesquioxane (mPOSS), which has eight methacryl groups tethered with a cage-like hybrid inorganic-organic nanostructure, for bone tissue engineering applications. Blending mPOSS with PPF was found to decrease the viscosity of PPF, expedite photo-crosslinking process, increase tensile modulus and accelerate hydrolytic degradation of crosslinked PPF/mPOSS while it did not significantly alter surface wettability, protein adsorption, and cell response. Chapter 3 demonstrates a polymer blend composed of amorphous PPF and semicrystalline poly(ε-caprolactone) (PCL), a widely used biocompatible and biodegradable polymer, in both uncrosslinked and photo-crosslinked forms. Thermal, rheological, mechanical properties as well as surface hydrophilicity and morphology can be well controlled by crosslinking density and crystallinity. Distinct cell attachment, spreading, and proliferation have been found to PPF/PCL blends in the presence or absence of cross-links. Chapter 4 and 5 describe the crystallization induced banded spherulitic morphologies in PPF/PCL blends and PCL homo-blends and their preliminary biological evaluation. Thermal properties, crystallization kinetics, and surface morphology of these blends can be regulated by isothermal crystallization temperature and composition. Surface roughness has been found to play an important role in influencing protein adsorption and cell response. Chapter 6 introduces a newly synthesized biodegradable elastomer, poly(ε-caprolactone) triacrylate (PCLTA), with two different molecular weights resulting in distinct mechanical properties at physiological temperature. Using replica molding from silicon wafers, photo-crosslinked PCLTA substrates with concentric micro-grooves have been successfully fabricated. MC3T3 cell attachment, proliferation, and differentiation could be better supported by stiffer substrates while not significantly influenced by micro-groove dimensions. Cell orientation, nuclei shape and localization, mineralization, and gene expression level of osteocalcin have been found to be more significant on narrower micro-grooves when groove depth was 10 μm.

Planar supported, polymerized phospholipid bilayers (PPBs) composed of 1,2-bis[10-(2’,4’-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphocholine (bis-SorbPC or BSPC) were generated by a redox polymerization method. The PPBs were supported by a silicon substrate. The PPBs were characterized and tested for uniformity and stability under physiological conditions. The PPBs were analyzed in vitro with murine derived cells that are pertinent to the host response. Cellular attachment and phenotypic changes in RAW 264.7 macrophages and NIH 3T3 fibroblasts were investigated on PPBs and compared to bare silicon controls. Fluorescent and SEM images were used to observe cellular attachment and changes in cellular behavior. The PPBs showed much lower cellular adhesion for both cell lines than bare silicon controls. Of the cells that attached to the PPBs, a very low percentage showed the same morphological expressions as seen on the controls. The hypothesis generated from this work is that defects in the PPBs mediated the cellular attachment and morphological changes that were observed. Finally, a layer-by-layer (LbL) deposition of a poly(acrylic acid) (PAA) and poly(N-vinylpyrrolidone) (PNVP) alternating bilayer was attempted as a proof of concept for future modification of this system.

Chitosan is widely investigated for biomedical applications due to its excellent properties, such as biocompatibility, biodegradability, bioadhesivity, antibacterial, etc. In the field of neural engineering, it has been extensively studied in forms of film and hydrogel, and has been used as scaffolds for nerve regeneration in the peripheral nervous system and spinal cord. One of the main issues in neural engineering is the incapability of neuron to attach on biomaterials. The present study, from a new aspect, aims to take advantage of the bio-adhesive property of chitosan to develop chitosan-based materials for neural engineering, specifically in the fields of brain repair and neuroprosthetics. Neuronal responses to the developed biomaterials will also be investigated and discussed. In the first part of this study (Chapter II), chitosan was blended with a well-studied hydrogel material (agarose) to form a simply prepared hydrogel system. The stiffness of the agarose gel was maintained despite the inclusion of chitosan. The structure of the blended hydrogels was characterized by light microscopy and scanning electron microscopy. In vitro cell studies revealed the capability of chitosan to promote neuron adhesion. The concentration of chitosan in the hydrogel had great influence on neurite extension. An optimum range of chitosan concentration in agarose hydrogel, to enhance neuron attachment and neurite extension, was identified based on the results. A “steric hindrance” effect of chitosan was proposed, which explains the origin of the morphological differences of neurons in the blended gels as well as the influence of the physical environment on neuron adhesion and neurite outgrowth. This chitosan-agarose (C-A) hydrogel system and its multi-functionality allow for applications of simply prepared agarose-based hydrogels for brain tissue repair. In the second part of this study (Chapter III), chitosan was blended with graphene to form a series of graphene-chitosan (G-C) nanocomposites for potential neural interface applications. Both substrate-supported coatings and free standing films could be prepared by air evaporation of precursor solutions. The electrical conductivity of graphene was maintained after the addition of chitosan, which is non-conductive. The surface characteristic of the films was sensitively dependent on film composition, and in turn, influenced neuron adhesion and neurite extension. Biological studies showed good cytocompatibility of graphene for both fibroblast and neuron. Good cell-substrate interactions between neurons and G-C nanocomposites were found on samples with appropriate compositions. The results suggest this unique nanocomposite system may be a promising substrate material used for the fabrication of implantable neural electrodes. Overall, these studies confirmed the bio-adhesive property of chitosan. More importantly, the developed chitosan-based materials also have great potential in the fields of neural tissue engineering and neuroprosthetics.