Because of their important role in many areas of science and technology, polymer brushes have been extensively studied theoretically and experimentally. In the first part of my thesis, in order to understand the molecular weight behavior of polymer brushes, a new method to cleave polymer brushes were investigated. A new inimer (having both an initiator and monomer fragment) was synthesized. After growing polymer brushes from these inimers containing cleavable linkages, the polymer brush layers were characterized by various techniques. The brush chains were cleaved and collected, providing an opportunity to study and compare polymer grown in solution vs. polymer grafted from the inimer-inbedded surfaces. Molecular weight differences were determined since it has been assumed, but not confirmed, that polymers synthesized in both manners should have the same molecular weight. Since growing a brush layer from a photopolymer (PP) layer is different than growing brushes from the surface directly, the first part of my thesis is dedicated to showing the differences between these two surfaces and how the PP network affects the brush growth with using different characterization methods such as neutron reflectivity and secondary ion mass spectroscopy. These studies helped to understand the characteristic behavior of the polymer brushes such as where the initiation occurs, how the inimer concentration affects on the photopolymer properties. The next part of my thesis is about the possible applications of polymer brushes. We examined the antibacterial effects of –onium salts and enzymes attached to polymer brushes. It is already known that -onium salts can be used as antibacterial agents in solution. They can kill both Gram-positive and Gram-negative bacteria. In our case, polymer brushes were grown from the PP layer spin-coated on glass substrates, and we investigated their antibacterial effectiveness of these polymer brushes. Phosphonium salts and lysozyme were used as antibacterial agents. Lysozyme was chosen since it is biocompatible and can be used inside the body. Lastly, azobenzene-containing photoresposive polymer brushes were prepared and the surface properties before and after UV exposure were observed. The surface wettability changes dramatically, and using only UV light is one of the safest and cleanest way to alter surface properties.

This thesis describes research in the control over long-range order and orientation of porous nanoscale materials and liquid mobility on surfaces with patterned chemistry and topography. A variety of researches will cover the topics ranging from preparation of ordered block copolymers and anodized aluminum oxides, and dynamic wettability on chemically patterned wafers with or without topography. The structure evolution of BCP thin films exposed with binary solvent mixture vapors at different temperatures will be investigated by scanning force microscopy and grazing incidence small angle X-ray scattering. The swollen thin films will undergo typical phase separation depending on thickness, temperature, and exposure time, which will determine the morphology of the resulting porous templates. A new approach for preparing ordered nanoporous AAO will be demonstrated using the pattern transfer of BCP structures to the surface of aluminum. By solvent annealing the BCP films in solvent vapor, arrays of cylindrical microdomains with a high degree of lateral order will be produced. Using reactive ion etching, the template of the nanoporous film will be transferred to the Al surface and the subsequent anodization in a concentrated acid solution will generate channels with the center-to-center distance and lateral order of the BCP film. A study of drop mobility on a surface with patterned wettability will be the final topic in the thesis. Silane chemistry, selective etching, and microcontact printing will be used to prepare designs on chemically patterned wafers with topography. The samples will have two different areas; one on which a liquid drop will move easily and another that will restrict its motion. Dynamic contact angle measurements will then be performed on the surfaces to determine the effect on drop mobility. The objective is to show that both contact angle and contact angle hysteresis are important in regards to drop mobility. The growth of condensed water droplets on these surfaces will be viewed and recorded.

Naturally occurring horse spleen ferritin (HSF) bionanoparticles (BNPs) (12 nm in diameter) with magnetic cores (8 nm in diameter) are distinct from synthetic nanoparticles due to their perfectly defined size and shape, and abundant amino acid surface functionality. The theme of this thesis is the use of HSF BNPs as nanoscale building blocks for surface functionalization and directed assembly. Bioconjugation grafting chemistry was utilized to tailor the surface properties of HSF BNPs, and interfacial assembly techniques were applied to control the ordering of BNPs and integrate the functionalized BNPs into composite materials. By taking advantage of surface available amines on the exterior surface of ferritin BNPs, norbornene functionalities were attached by amidation of an N-hydrosuccimide (NHS)-functionalized norbornene. Norbornene functionalized ferritin BNPs were co-assembled with norbornene-functionalized CdSe/ZnS quantum dots at an oil/water interface to form robust, ultra-thin films and capsules upon crosslinking by means of ring-opening metathesis polymerization (ROMP). Ordered hexagonal arrays of gold nanodots on a silica substrate were prepared by block copolymer micelle lithography. PEGylated alkane thiols attached to ferritin BNPs enabled a specific interaction of BNPs with the gold nanodots through a thiol-gold linkage. As a result of the guided assembly of ferritin BNPs on the gold nanodots, highly ordered ferritin BNP arrays were achieved over a large area, and confirmed by grazing incidence small angle X-ray scattering (GISAXS). Grafting chemistry was performed to grow poly(methacryloyloxyethyl phosphorylcholine) (polyMPC), and poly(PEG methacrylate) (polyPEGMA), chains from the surface of ferritin BNPs using atom transfer radical polymerization (ATRP). The resulting hydrophilic polymer coatings were found to have a distinct impact on the recognition properties of the ferritin BNPs, as seen in their suppressed interactions with thin film polymer templates, and their resistance to antibody recognition. The solubility of polyPEGMA-coated ferritin nanoparticles in organic solvents enables their dissolution in the block copolymer polystyrene-b-poly (ethylene oxide) (PS-b-PEO), and selective integration into the PEO domains of microphase-separated copolymer nanostructures by self-assembly. This approach provides yet another interfacial assembly strategy to control the spatial distribution of polymer-grafted ferritin BNPs.

Nanoimprint lithography (NIL) has established itself as a competitive, high resolution and cost efficient alternative to standard photolithographic technologies. In the pursuit of the use of NIL in microelectronic and energy applications, such as fabrication of interlayer dielectrics and hybrid solar cells, we present our study on porous dielectrics and semiconductor nanowires generated by NIL. First, we developed a facile but powerful manufacturing route to fabricate air gap dielectrics with well-defined pore geometries. A thermally labile organic polymer, denoted as sacrificial template, was patterned using thermal NIL and embedded in a lowk dielectric thin film. Air gap nanochannels in the dielectric layer were obtained by selective removal of the patterned, sacrificial polymer through thermal degradation. Various process conditions such as film deposition, imprint, etch, and calcination were studied to deduce their effect on the air gap dielectric film formation. By finely tuning these parameters, crack free air gap dielectric films were produced. Introduction of air gaps effectively lowered the dielectric constant of the dielectric material since air has a dielectric constant of unity. These air gap structures demonstrated excellent electrical, thermal and mechanical properties making them attractive candidates as interlayer dielectrics for next-generation integrated circuit (IC) applications. In addition, we explored the suitability of the nanochannel dielectrics as fluidic devices and demonstrated successful fluid transport through these channels by fluorescence dye infusion experiments. Inspired by the above methodology, we further developed a new, potentially low-cost and high-throughput technique to fabricate highly crystalline, continuous cadmium selenide (CdSe) semiconductor nanowires by successfully merging electrodeposition and soft nanoimprint lithography. By utilizing nanoimprint patterned photoresists as templates during the electrodeposition step and subsequent resist lift-off, we were able to generate continuous parallel arrays of CdSe nanowires, each wire having dimensions dictated by the imprint mold. We demonstrated that the electrodeposited nanowires were highly crystalline and their crystalline structure was unaffected by the lift off process. Our method allowed production of well-aligned CdSe semiconductor nanowire arrays of precisely controlled diameter and length and led to a substantial improvement over the control in nanowire orientation compared to existing technologies. This economic and relatively simple approach can easily be implemented and adapted to various semiconductor systems and is expected to be used in photovoltaic applications.

Controlling the morphology of thin films is key in optimizing the efficiency of polymer-based photovoltaic (PV) devices. The morphology and interfacial behavior of the multicomponent active layers confined between electrodes are strongly influenced by the preparation conditions. Results obtained in this work quantitatively show the photovoltaic device performance is strongly affected by the nanoscopic morphology, crystal orientation, composition distribution and the interdiffusion behavior of the photoactive layer. To better understand the physics of the photoactive layer in the organic photovoltaic devices, it is necessary to gain a quantitative understanding of the morphology and the manner in which it develops. A key element in the kinetics associated with the structure development is the interdiffusion of the components. To that end we used poly(3-hexylthiophene) (P3HT) / [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bilayers as a model to investigate the interdiffusion of the components and its role in the development of the morphology. A detailed description of the diffusion behavior and the morphology developed from a layer of P3HT in contact with a layer of PCBM during thermal annealing is given. Amorphous P3HT and PCBM are shown to be highly miscible and PCBM can penetrate into the P3HT layer through the P3HT amorphous region and form the bulk heterojunction structure within a few second of annealing at 150°C. The results indicated that one phase is a pure P3HT crystal domain and the other phase is the mixture of amorphous P3HT and PCBM, which is not consistent with a phase separation of the components by a spinodal decomposition mechanism. We put forth an alternative mechanism, namely a competitive crystallization/diffusion argument, to describe the origin of the morphology. These findings provide new insights and guidance in the generation of active layers in organic photovoltaics that are crucial in enhancing the device performance. Textured organic solar cells were also studied, providing another route to fabricate higher performance devices.

This dissertation describes research performed using siloxane polymers. This includes the reactions of siloxane polymers with inorganic oxide surfaces to form covalently attached monolayers, and the electrical properties of crosslinked silicone composite films fabricated by compounding with nickel particles. In addition to these topics, the use of contact line pinning as a practical and controllable method for the deposition of materials on superhydrophobic and chemically patterned surfaces is also described. The first chapter provides a general review of siloxane polymer chemistry, focusing in particular on the relationship between molecular structure and physical properties. The use and fabrication of silicone composite materials is also discussed, including typical methods for crosslinking siloxane polymers and the effects of filler materials. Finally, contact angle hysteresis and contact line pinning phenomena are presented. Following this introduction, four separate but interrelated projects are presented. First, the surface modification of titania via hydridomethylsiloxanes is discussed. This work represents an extension of the reaction of hydridosilanes and provides an environmentally clean method for the hydrophobization of titania. Linear and cyclic hydridomethylsiloxanes, as well as hydridomethylsiloxane-co-dimethylsiloxane polymers, are used as reagents and the resulting surfaces are discussed. Unpredicted results from this method lead to the consideration of poly(dimethylsiloxane) as a previously unconsidered reagent presented in the next project. The second project discusses the covalent attachment of siloxane polymers, particularly poly(dimethylsiloxane), to a range of inorganic oxide surfaces, including titania, nickel oxide, alumina, and silica. This reaction is presented as a thermally activated equilibrium process, and offers insight into certain aging processes found in silicone materials. Particular focus is made on the development of a highly reproducible method for the fabrication of low contact angle hysteresis surfaces. Furthermore, this reaction is shown to be general for the siloxane bond through the reaction of functional and cyclic siloxanes. The third project describes the preparation of electrically conductive silicone coatings, containing nickel and titania particles. The effect of nickel concentration and geometry on the electrical properties of these coatings is examined and the effects on the percolation threshold are presented. In addition to this, the addition of titania nanoparticles to diminish electrical conductance is also investigated. The fourth project discusses the contact line pinning of liquids on hydrophobic surfaces. In this chapter, the use of ionic liquids exhibiting no vapor pressure is used to experimentally determine the de-wetting process of liquids from pillared, superhydrophobic surfaces through micro-capillary bridge rupture. Furthermore, this technique is used as a preparative technique for the fabrication of individual salt crystals supported on pillared surfaces.

This dissertation describes research carried out in the area of siloxane polymers, which refers to a group of polymers based on alternating silicon-oxygen backbones. The inexpensive starting materials and extraordinary thermal, mechanical and optical properties make siloxane polymers promising materials in a lot of applications, such as lithography, optical devices, self-healing materials and ion conducting membranes. Four projects are described after the introduction section. In the first project, extremely crosslinked silicone networks with novel structure are prepared by hydrosilylation of two tetra-functional cyclic monomers, 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) and 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilxane (D4V). By introducing cyclic structures into the network and increasing the crosslink density, the thermal stability is improved, the Young's modulus and hardness of these siloxane networks are also be enhanced. In addition, some traditional properties of PDMS have been reserved, such as UV transparency, low surface tension and being reaction injection moldable. The second project involves using the extremely crosslinked silicone network from the first project as a replica material for both nanoimprint lithography (NIL) and capillary force lithography (CFL). Because the advantageous properties of D4H-D4V networks meet all the requirements of NIL and CFL, such as UV transparency for photo nanoimprint lithography, thermal stability for high printing temperatures, high modulus for high printing pressures, low surface energy for easy demolding and molecular smoothness for achieving small scale features, this material was tested to fabricate sub-25 nm scale patterns from blu-ray discs and sub-9 nm scale patterns from anodized aluminum templates. The third chapter describes a study on thermal reconstruction of oxygen plasma-treated poly(dimethylsiloxane) networks with controlled crosslink density. Instead of using a commercial product, e.g. Dow Corning Sylgard 184, pure silicone networks were prepared by hydrosilylation of various monomers and/or precursors. The relationship of reconstruction rate versus crosslink density is described. The fourth project involves in surface modification of extremely crosslinked silicones using a chemical method. A stable hydrophilic surface was prepared by peroxide oxidation. After incorporating silanol groups on the surface, subsequent modifications with various reactive silanes were conducted and control of surface properties was demonstrated. The hydrophilic surfaces show similar reactivity to that of oxidized silicon wafers. The last chapter describes a "living" siloxane network which has been used as a self-healing material. Through ring opening polymerization of octamethylcyclotetrasiloxane (D4) and bis(heptamethylcyclotetrasiloxanyl)-ethane (bis-D 4) in the presence of a quaternary ammonium catalyst, "living" siloxane networks with controlled crosslink density were prepared. Based on the equilibrium of cyclic and linear species, the "living" networks exhibit "self-healing" abilities and can be "reshaped" via chemical stress relaxation upon application of external mechanical stress. (Abstract shortened by UMI.)

Hydrogels, a class of materials composed of polymer networks swollen with large amounts of water, have gained increasing attention in a range of fields, from tissue engineering to food science. However, synthetic hydrogels are known to be brittle and have poor mechanical properties, including low extension ratios and fracture toughnesses. It has been a great challenge to develop synthetic hydrogels with improved mechanical properties and correlate with their network composition. In this dissertation we developed two robust well-defined synthetic hydrogel systems by two simple strategies—thiol-norbornene chemistry and ring opening metathesis polymerization (ROMP). The swelling and mechanical properties were systematically characterized and correlated with their network structures. The PEG/PDMS hydrogels synthesized by the simple, efficient, photo-initiated thiol-norbornene chemistry have improved mechanical properties. By manipulating the volume fractions of the PEG and PDMS, a large range of water content (54%–97%) was achieved. The Young's modulus (E) was significantly improved by increasing the volume fraction of PDMS in the hydrogel, and the Voigt and Reuss models were used to quantify the relationship between the volume fraction and E. In addition, increasing the volume fraction and molecular weight of the PDMS led to tougher hydrogels with Gc more than 100 J/m2. Furthermore, a high resilience (more than 97%) was maintained across the entire range of strains, regardless of the composition of the PEG/PDMS hydrogels. Controlled polymerization provides another method to synthesize gels with improved mechanical performance. The properties of the ROMP-based gels were tuned by varying the initial molar ratio of the monomer to cross-linker from 7.5% to 20%. The mechanical properties of the gels were characterized via the cavitation rheology technique (CRT), which demonstrated a transition from reversible to irreversible deformation with the increase of the molar ratio. By combining CRT and contact mechanics, E and Gc for these gels were quantified. As the amount of the cross-linker increased, E increased while G c slightly decreased. Soft tissues with hierarchical structures share similar properties as synthetic hydrogels. The study of their mechanical properties would provide useful information in designing synthetic hydrogels with novel network structures. Eye lens was chosen in this study. The anisotropic mechanical properties of bovine eye lenses were measured using CRT over a range of length scales. E of the nucleus and cortex of the lens were determined, as approximately 11.8 and 0.8 kPa, respectively, on macroscopic length scales. We also measured the mechanical properties of the lens on a length scale of a single cell, suggesting that the stiffness significantly decreased from that in the bulk measurements for both the nucleus and cortex. In addition, during the growth of the cavity anisotropic propagation in the cortex was observed, while in the nucleus, the propagation was isotropic. We further explored the elasticity of the cavity deformation, showing both elastic and inelastic deformation occurred in the nucleus with equal contributions while deformation in the cortex was elastic and reversible. Lastly, we investigated adhesive properties of polymer networks with the thiol-norbornene chemistry to explore their possible applications. The mechanical and adhesive properties of these PDMS networks were quantified by the contact adhesion test (CAT), as well as DMA and compressive measurements. E of these end-linked PDMS measured by CAT was comparable with that measured by the compressive test. In terms of the adhesion properties, the energy release rate was described as a function of crack velocity. A higher molecular weight between cross-links led to a higher adhesion energy over a range of crack velocity for the PDMS with the same end-linking chemistry. Sylgard PDMS with 18 to 1 ratio was chosen to compare the mechanical and adhesive properties to the end-linked PDMS. With the similar Young's modulus and resilience, the adhesion energy of the Sylgard PDMS was comparable to that of the end-linked PDMS with 5 kDa molecular weight, which was likely to result from the comparable molecular weight between cross-links.

Conjugated polymers are of interest in organic photovoltaics (OPVs) for the benefits of their low cost, ease of processing, and flexible design. OPV device performance greatly depends on the morphology of the donor (conjugated polymer) and acceptor (fullerene, CdSe, etc.) materials, which should ideally promote efficient exciton formation, dissociation, and charge transport to the respective electrodes. One potentially ideal active layer morphology would consist of an interpenetrating, bicontinuous network of donor and acceptor materials, having domain sizes of ∼10 nm (i.e., on the order of the exciton diffusion length). Such morphologies can be achieved through annealing processes (thermal or solvent) of the donor/acceptor blend, or the use of pre-formed, highly crystalline fibril nanowires of the conjugated nanowires. This thesis outlines the design of functional polythiophene copolymers with the ability to form novel assemblies through tailored functionalities. Amphiphilic P3HT-b-poly(3-(triethyleneglycol)thiophene) (P3TEGT) diblock copolymers were synthesized that were capable of microphase separating based on the difference in polarity between the blocks. We targeted P3HT-b-P3TEGT thin-film morphologies, where we could orient [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (electron acceptor) in the polar P3TEGT domain, to allow P3HT to form pristine crystal domains. Thermal annealing P3HT-b-P3TEGT diblock copolymers led to microphase separation, as characterized by atomic force microscopy (AFM) and small-angle x-ray scattering (SAXS), and OPV devices were fabricated and characterized using P3HT-b-P3TEGT/PCBM blends. P3HT-based diblock copolymers that had hydroxyl- and amine- functionalities were synthesized in an effort to utilize their nucleophilic nature for further functionalization. These copolymers underwent a solvent-induced crystallization that provided a P3HT nanowire decorated with the hydroxyl/amine functionalities on the fibril exterior. Previously, cross-linking mechanisms for polythiophenes had occurred in thin films upon thermal annealing or exposure to radiation, with little control over the crystallinity of the polymer. We were able to utilize fibrils formed from our functional diblock copolymers to covalently cross-link the crystalline structures by reacting with diisocyanates. This led to the formation of robust fibrils that had not previously been reported, that maintained photophysical and electronic properties to the unmodified nanowires. These nucleophilic fibrils were reacted with a bis-diisocyanate functionalized fullerene derivative to yield stabilized p-type/n-type nanowires. This process led to robust p-type/n-type fibrils that displayed photoluminescence quenching and high charge transfer characteristics that were not observed for p-type/n-type blends. In an effort to simplify the fibril cross-linking, we designed a P3HT-based diblock copolymer that had thioacetate functionalities, which were deprotected and underwent an oxidative cross-linking process. These polymers formed nanowires by solvent induced precipitation, and upon deprotection of the thioacetate groups by reaction with dimethyl amine, experienced oxidative cross-linking to achieve robust fibrils. This provided a novel system in that the polymer was able to cross-links itself, and the cross-linking process was found to be reversible by reduction chemistry.

This dissertation aims to both deepen and broaden our understanding of copolymers with pendent benzophenone (BP) in relation to both established applications and novel directions in materials science. Photo-reaction of these BP copolymers is explored in attempts to achieve three distinct goals: (1) robust and efficiently photo-crosslinkable solid polymer films, (2) photo-reacted polymer blends with disordered bicontinuous nanostructures, and (3) photo-patterned hydrogel materials with environmental UV stability. We begin by investigating the fundamental gelation behavior of solid polymer films, finding BP copolymers to be particularly effective crosslinkable materials. Gelation efficiency can be tuned according to comonomer chemistry, as BP hydrogen abstraction on the main polymer chain increases chain scission, reducing crosslinking efficiency. This knowledge is then applied in Chapter 3, wherein we discuss two potential methods for preparing nanostructured polymer blends from these copolymers, namely spinodal decomposition of a photo-crosslinked polymer blend and solution-state photografting to create interfacially active species. While each technique shows promise, the ultimate goal of a disordered bicontinuous morphology will require further tuning of materials systems and protocols. Finally, chemical deactivation of BP photo-crosslinker in copolymers for use as photo-patternable and environmentally stable hydrogel materials is investigated. Reduction of BP by sodium borohydride proves a feasible route toward deactivating residual photo-crosslinker in patterned hydrogel films. These results confirm the utility of copolymers with pendent benzophenone photo-crosslinkers as useful tools for complex material systems.