Mechanical properties of (woven carbon fiber / vinyl ester matrix) composites can be greatly improved if the interphase between the reinforcing high-strength low-weight fiber and the thermoset resin is made more compliant. In order to improve the adhesion of the vinyl ester matrix to the carbon fiber, a thermoplastic coating such as poly(vinyl pyrrolidone) (PVP) can be used as an intermediate between the matrix and the fiber. The extent of mutual diffusion at the (sizing material / polymer matrix) interphase plays a critical role in determining the mechanical properties of the composite. In this research, the molecular interdiffusion across a poly(vinyl pyrrolidone))/vinyl ester monomer (PVP/VE) interface is being investigated by Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) spectroscopy. The ATR method which can be used to characterize the transport phenomena, offers several advantages, such as the ability to monitor the diffusion <I>in situ</I> or to observe chemical reactions. In order to separate the effects of the vinyl ester monomer diffusion and the crosslinking reaction, ATR experiments were carried out at temperatures below the normal curing temperature. Diffusion coefficients were determined by following variations in infrared bands as a function of time, and fitting this data to a Fickian model. The values of the diffusion coefficients calculated were consistent with values found in the literature for diffusion of small molecules in polymers. The dependence of diffusion coefficients on temperature followed the Arrhenius equation. Hydrogen bonding interactions were also characterized. The diffusion model used in this study, however, does not seem to be appropriate for the particular (PVP/VE) system. Because the glass transition temperature of the PVP changed as diffusion proceeded, one would expect that the mutual diffusion coefficient did not stay constant. In fact, it was shown that the Tg can drop by 140oC during the diffusion process. A more suitable model of the (PVP/VE) system should take into account plasticization, hydrogen bonding, and especially a concentration dependent diffusion coefficient. Further analysis is therefore needed. / Master of Science

Additive manufacturing (AM) creates 3D objects out of polymers, ceramics, and metals to enable cost-efficient and rapid production of products from aerospace to biomedical applications. Personalized products manufactured using AM, such as personalized dosage pharmaceuticals, tissue scaffolds, and medical devices, require specific material properties such as biocompatibility and biodegradability, etc. Polymers possess many of these qualities and tuning molecular structure enables a functional material to successfully deliver the intended application. For example, water-soluble polymers such as poly(vinyl pyrrolidone) and poly(ethylene glycol) both function as drug delivery materials because of their inherit water-solubility and biocompatibility. Other polymers such as polylactide and polyglycolide possess hydrolytically cleavable functionalities, which enables degradation in the body. Non-covalent bonds, such as hydrogen bonding and electrostatic interactions, enable strong connections capable of holding materials together, but disconnect with heat or solvation. Taking into consideration some of these polymer functionalities, this dissertation investigates how to utilize them to create functional biomedical products using AM. The investigation of structure-property-processing relationships of polymer molecular structures, physical properties, and processing behaviors is transforming the field of new materials for AM. Even though novel, functional materials for AM continue to be developed, requirements that render a polymeric material printable remain unknown or vague for most AM processes. Materials and printers are usually developed separately, which creates a disconnect between the material printing requirements and fundamental physical properties that enable successful printing. Through the interface of chemistry, biology, chemical engineering, and mechanical engineering, this dissertation aims to relate printability of polymeric materials with three types of AM processes, namely vat photopolymerization, binder jetting, and powder bed fusion. Binder jetting, vat photopolymerization, and powder bed fusion require different viscosity and powder requirements depending on the printer capabilities, and if the material is neat or in solution. Developing scaling relationships between solution viscosity and concentration determined critical overlap (C*) and entanglement (Ce) concentrations, which are related to the printability of the materials. For example, this dissertation discusses and investigates the maximum printable concentration in binder jetting of multiple polymer architectures in solution as a function of C* values of the polymer. For thermal-type printheads, C* appeared to be the highest jettable concentration, which asserted an additional method of material screening for binder jetting. Another investigation of the photokinetics as a function of concentration of photo-active polymers in solution revealed increased viscosity leads to decreased acrylate/acrylamide conversion. Lastly, investigating particle size and shape of poly(stearyl acrylate) particles synthesized through suspension polymerization revealed a combination of crosslinked and linear polymers produced high resolution parts for phase change materials. These analytical screening methods will help the progression of AM and provide future scientists and engineers a better guideline for material screenings. / Doctor of Philosophy / Additive manufacturing (AM), also known as 3D printing, enables the creation of 3D objects in a rapid and cost-efficient manner for applications from aerospace to biomedical sectors. AM particularly benefits the field of personalized biomedical products, such as personalized dosage pharmaceuticals, hearing aids, and prosthetic limbs. In the future, advanced detection and prevention medical screenings will provide doctors, pharmacists, and engineers very precise data to enable personalized healthcare. For example, a patient can take three different medications in one pill with the exact dosage to prevent side-effects and drug-drug interactions. AM enables the delivery and manufacturing of these personalized systems and will improve healthcare in every sector. Investigations of the most effective materials is needed for personalized medicine to become a reality. Polymers, or macromolecules, provide a highly tunable material to become printable with slight chemical modifications. Investigation of how chemical structure affects properties, such as strength, stretchability, or viscosity, will dictate how they perform in a manufacturing setting. This process of investigation is called "structure-property-processing" relationships, which connects scientists and engineers through all disciplines. This method is used to discover which polymers will not only 3D print, but also carry medication to a patient or deliver therapeutics within the body.

There has been growing interest in designing and development of suitable micro or nano drug delivery system with the ability to target site specifically and release the payload in a predetermined fashion. Recently a new type of system called polyelectrolyte microcapsules and thin films have been proposed and developed for applications such as, biomedical devices to micro sensing and drug delivery. Owing to its advantages of mild preparation conditions, multifunctionality, with programmable characteristics and to encapsulate large amount of materials, it has shown immense potential. In the present research, multilayer polyelectrolyte thin films composed of Poly(methacrylic acid) (PMA) and Poly (vinyl pyrrolidone) (PVP) were deposited on the flat substrates using layer by layer (LBL) technique. The film growth and its deconstruction under physiological conditions were characterized using UV Visible spectrophotometer and Scanning Electron Microscopy (SEM). Hollow microcapsules composed of PMA and PVP were also produced with the help of sacrificial silica template using the same LBL adsorption technique. After coating the desired number of PVP and PMA layers, the colloidal template was removed with a buffer system composed of Hydrofluoric acid (HF) and Ammonium fluoride (NH4F). The obtained capsules were characterized for its surface morphology using SEM and Atomic Force Microscopy (AFM). The hydrogen bonding in capsule formation was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Encapsulation and release with the microcapsules was carried out using Rifampicin (Antitubercular drug) as a model drug. The interaction of empty and drug loaded capsules with Mycobacterium Smegmatis cell line was investigated. It was found that the empty capsules did not affect the cell growth indicating their biocompatibility. Confocal microscopy studies with Doxorubicin (anticancer drug), which is a naturally fluorescent molecule, showed the drug is indeed encapsulated inside the hollow capsule. From the above studies, it was concluded that polyelectrolyte capsules have the potential to be used for delivering drugs.