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Abstract: There is growing interest in the formulation and application of nano colloids + non-adsorbing polymer in fields of nanomedicine, hydrocarbon production, and environmental science. Successful applications rely on a detailed understanding of the related fluid thermophysical and thermochemical properties. Polymer + solvent binary mixtures exhibit liquid-liquid phase behavior at low temperature. This behavior, driven by repulsive interactions between the globular conformation of the polymer, possess an UCEP temperature because the polymer undergoes a conformational change. From a Gibbs free energy perspective, at temperatures slightly above the UCEP temperature, a single-phase liquid is marginally stable. This phase behavior is driven by entropically favourable molecular interactions between polymer in the coil conformation and solvent molecules. Phase diagrams for nanoparticle + non-adsorbing polymer + solvent ternary mixtures typically exhibit colloid gas, G (a liquid comprising largely polymer and solvent), a colloid liquid, L (a liquid comprising largely solvent and colloid) and a colloid phase, C (a largely nanoparticle rich phase) phases. The phase behaviors GC, GL, LC and GLC at equilibrium are driven by depletion flocculation (a surface phenomenon). This work focuses on the interaction between these two phenomena – depletion flocculation and molecular liquid-liquid phase behavior based on the behavior of polystyrene + cyclohexane + nano silica particles. For example, above the UCEP temperature, even a trace mass fraction of silica nanoparticle (

Stimuli-responsive polymeric materials have been now widely researched toward the biomedical applications including therapeutic delivery, bio-sensor surface modification, and tissue-engineering, etc., considering their desirable biocompatibility, tunable properties, and sensitivity toward physiological stimuli. Beyond the monoresponsive materials, polymers with responsiveness simultaneously toward multiple stimuli are paid great attention to because the control of responsive behaviors could be achieved at a more accurately and delicately level in a complex local environment. However, many challenges still exist such as maintaining integrity of the structure, shaping the morphology at micro- and macro-scale, and regulating a controllable and predictable transition behavior. The objectives of this dissertation are to develop and optimize multi-responsive polymeric materials toward the physiological stimuli including temperature, pH, and oxidative stress, in the forms of nano-/micro-scaled particles, nano-scaled multilayers, and macro-porous scaffolds. Specifically, micro/nano-scale polyetheramine containing hydrogel particles with pH-, thermo-, and oxidation-responsiveness were developed via thermally induced phase separation for therapeutic delivery (Chapter 2). The physical properties, including size, surface charge density, swelling behaviors are tunable via varying the preparation parameters such as monomer ratio, reaction time and temperature, monomer concentration, and monomer composition. Cytocompatibility and drug loading capability were investigated, and proved these particles to be of great potential for biomedical applications. For construction of dual-responsive multilayers, pH sensitivity was incorporated into a thermo-responsive polymer (poly(N-vinyl-2-caprolactam)) (PVCL) via bearing a tert-butoxycarbonylmethyl group at the 3-position of VCL through the approach of nucleophilic substitution (Chapter 3). The biocompatibility exhibited in acute cytotoxicity assay and the successful layer-by-layer self-assembly with a cationic polymer suggested a possible application for bio-sensor surface modification. Macro-porous hydrogels with pH-, thermo-, and oxidation-responsiveness were successfully fabricated via thermally-induced phase separation of prepolymers toward the application as scaffolds for neuronal regeneration (Chapter 4). The hydrogels exhibited micro-sized interconnected cavity for diffusion of nutrition and metabolites, hydrophobic domains for therapeutic delivery, great biocompatibility in direct contact assay, and cationic functional groups for survival of neuronal cells as well as neurite outgrowth, indicating a probable use for neuronal regeneration.

Michael Simons. M.S., Department of Chemistry, Wright State University, 2007. Hydrophobically Modified Polyethyleneimines and Ethoxylated Polyethyleneimines. The modification of the commercially available polymers polyethyleneimines and ethoxylated polyethyleneimines took place with approximately a 3-10% alkylbromide modification followed by, in the case of the polyethyleneimines, a 2-hydroxypropyl modification, using propylene oxide, on the order of 65-70%. The objective was to increase the hydrophobicity of the polymer while keeping the cloud point above 60°C. Another approach taken was to form hydrophobic ethers from ethoxylated polyethyleneimine. We also added a 2-hydroxy ethyl group to a hexylated polyethyleneimine avoiding the use of ethylene oxide or drying EPI.