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<p>This study examined the self-trapping of light emitted by a miniature green laser in a photopolymerizable medium and the interactions between two parallel-propagating self-trapped beams. The work included the design and fabrication of an Intra-Cavity Frequency-Doubling (IC-FD) Nd: YVO₄/MgO: PPLN miniature green laser with a stable and tunable output intensity. Emission from this laser enabled a systematic examination of self-trapping phenomena at incident intensities spanning 8 orders of magnitude (3.2× W·cm^-2to 6368 W·cm^-2). When launched into a photopolymerizable medium, light emitted by the miniature green laser self-trapped by initiating polymerization and corresponding changes in refractive index along its propagation path. The evolution and dynamics of the self-trapped beam corresponded to the behaviour of self-trapped beams of coherent light. Interactions between a pair of parallel-propagating self-trapped beams were also characterised at a range of intensities. This study shows that the miniature green laser is an efficient, coherent source with a large range of output intensities for the excitation of self-trapped beams. This opens opportunities for its incorporation into small-scale optical systems designed to operate based on the generation and interactions of self-trapped beams.</p> / Master of Applied Science (MASc)

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.

Four potential new monomers were prepared, all of which were structural analogues of BisGMA (2,2-bis(4-(2-hydroxy-3-methacryloxyprop-1-oxy) phenyl)propane). The synthesis of these tetrafunctional dimethacrylate monomers was based on structural modifications of Bis-GMA in the core and the side chain and required a two-step reaction. The first step was propoxylation or ethoxylation of the bisphenols and the second step was the methacrylation of the resulting products. The core structures are designated by Bis-A for isopropylidene and 6F for hexafluoropropyl. The side chain structures were designated on the basis of the pendant side chains in the glycidyl moiety as -OH, -H, and -CH3 from the epichlorohydrin, ethyleneoxide, and propyleneoxide reaction products with the bisphenols, respectively. Bis-GMA was commercially obtained and used as a standard for comparison of the experimental monomers. All the monomers were prepared by the following general procedure of propoxylation or ethoxylation of the biphenols followed by methacrylation. They were characterized by NMR, FTIR, DSC and Cone and Plate Viscometry. All the experimental monomers exhibited lower viscosities and glass transition temperatures than the control, which was attributed to the elimination of the hydrogen bonding. The monomers were photopolymerized in a differential scanning calorimetry modified with an optics assembly (DPA 7; Double Beam Photocalorimetric Accessory) to study the photo-induced crosslinking reactions. The influence of monomer structure, temperature, light intensity, and initiator concentration on the photopolymerization kinetics of ethoxylated and propoxylated dimethacrylates was investigated by isothermal DSC. The DSC curves showed a rapid increase in rate due to the Trommsdorff effect, and then a decline due to the decrease of monomer concentration and the autodeceleration effect. The monomers with lower viscosities and glass transition temperatures exhibited higher conversions of the double bonds. The final extent of conversion increased with curing temperature, light intensity and initiator concentration. The radiation intensity exponent varied from 0.68 (BisGMA) to 0.74 for the ethoxylated 6F system. The initiator exponent were varied from 0.34 (for BisGMA) to 0.44 for the propoxylated BisA system. The ratio of the reaction rate constant (kt/kp) was calculated for PropBisAdm from both steady-state and non steady-state conditions. The effect of dilution on photopolymerization kinetics of BisGMA/triethyleneglycoldimethacrylate (TEGDMA) mixtures was also studied by isothermal photo-DSC. Dilution with TEGDMA significantly reduced the viscosity and glass transition temperatures of the mixtures due to the increase in the flexibility. The extent of polymerization increased with increasing TEGDMA and curing temperature. The calculation of ratio of rate constants (kt/kp) was also determined and the significance was discussed herein. / Master of Science

In recent years, triply periodic minimal surfaces (TPMS) have drawn much attention in research mainly due to their smooth, highly symmetrical surfaces, non-self-intersecting features, and mathematically controllable topologies. TPMS can have pre-defined physical and mechanical properties. The advancement of additive manufacturing technology enables us to fabricate these intricate geometric structures which was not possible by traditional manufacturing methods. In this study, the vat photopolymerization technique was used to manufacture Primitive, Gyroid, and Diamond structures. Samples were cured under ultraviolet (UV) rays after printing. Uniaxial compression experiments were conducted to assess the compressive modulus and strength of these lightweight structures. The compressive behavior of TPMS structures was also predicted using finite element analysis (FEA). Dynamic mechanical analysis (DMA) was used to compare the behavior of these structures at different temperatures. UV-cured samples exhibited improved thermo-mechanical characteristics. The primitive structure had the highest compressive strength among other structures. FEA also revealed the stress concentration areas for each sandwich structure. The DMA findings indicate that TPMS sandwich structures demonstrate significantly reduced storage modulus compared to solid structures. A numerical investigation was performed to understand the heat exchanger application of TPMS structures. The velocity profile, temperature, and pressure distributions were observed for the Primitive heat exchanger. The results of this investigation provide valuable information regarding the enhanced structural and thermal characteristics of these structures manufactured using vat photopolymerization.

Les procédés de photopolymérisation connaissent un développement important avec des applications considérables dans le milieu industriel en raison de ses avantages économiques et écologiques. Les réactions de photopolymérisation sont très représentées, elles reposent sur l’utilisation d’un composé ou d'un système photosensible sous irradiation, générant des espèces réactives capables d’amorcer la polymérisation et de réagir avec le monomère. Le principal objectif de ce travail de thèse consiste à développer des molécules efficaces comme photoamorceurs (PA) pour la photopolymérisation radicalaire (FRP) d’une part et la photopolymérisation cationique (CP) ou la photopolymérisation cationique sensibilisée par les radicaux (FRPCP) d’autre part. Nous nous sommes intéressés à des systèmes amorceurs hautes performances absorbant fortement dans le domaine du visible et permettant l’utilisation de lampes non nocives et à faible consommation d'énergie : les diodes électroluminescentes (LED). Ainsi, un procédé original portant sur la combinaison de la photopolymérisation radicalaire et la photopolymérisation cationique en une seule étape a été examiné. Cette approche a fait appel à la synthèse de réseaux interpénétrés de polymères (RIP) comportant les propriétés spécifiques de chaque polymère. Les efforts ont été consacrés au développement de nouveaux composés avec de nouvelles structures chimiques et d’excellentes propriétés d’absorption de lumière avec de coefficients d’extinctions molaires très élevés.Des systèmes construits sur l’utilisation de différentes structures comme photoamorceurs ont pu être mis au point dans le cadre de cette thèse. La possibilité d’utiliser des colorants présentant un caractère push-pull, ou des colorants étant caractérisés par une structure polyène ou une structure polyaromatique a pu être considérée. Egalement, des structures à base de xanthène sensibles dans le domaine proche visible ont pu être proposées. De plus, ce travail a permis d’étudier de nouveaux systèmes photoamorceurs à base de structures minérales telles que les polyoxométallates ou les pérovskites. Ainsi, la possibilité de proposer de nouveaux sels d’iodonium à base de coumarine a pu être démontrée. Des meilleures performances ont été atteintes en utilisant des systèmes photoamorceurs à deux composants (PA/Ph2I+) ou à trois composants (PA/Ph2I+/additif) dans des conditions d’irradiation douce. Afin d’étudier et caractériser ces photoamorceurs, la cinétique de la réaction de photopolymérisation a été suivie par spectroscopie infrarouge à transformée de Fourier (RT-FTIR). Les radicaux générés ont été détectés par résonance paramagnétique électronique (RPE). La photolyse laser éclair (LFP) a été utilisée comme technique complémentaire pour étudier l’efficacité et la réactivité de radicaux générés. / The photopolymerization reaction is used in an increasing number of industrial applications because of the remarkable performance of the process. The photopolymerization reactions require the presence of photosensitive compounds. These latter can absorb light and participate in the photoinitiation through the generation of reactive species. The main objective of this PHD was to develop efficient molecules as photoinitiators (PI) for the free radical photopolymerization (FRP), the cationic photopolymerization (CP) and the free radical promoted cationic photopolymerization (FRPCP). We were interested in new high performance photoinitiating systems (PISs) exhibiting excellent light absorption properties (especially in the visible wavelength range). The photopolymerization must be carried out under soft irradiation conditions (non harmful lamps, low energy consumption and low intensity sources: light-emitting diodes LED). Thus, a novel method involving concomitant radical/cationic photopolymerization in one step was examined. This approach involves the synthesis of interpenetrating polymer networks (IPNs) comprising the specific properties of each polymer. The efforts have been devoted to the development of new compounds with new chemical structures and excellent light absorption properties with high molar extinctions coefficients.Many PISs based on different photoinitiators structures have been developed in this work. The possibility to use dyes having a push-pull character, or dyes being characterized by a polyene or polyaromatic structures were considered. Also, originals xanthenes derivatives sensitive in the visible region have been proposed. In particular, this work has enabled the study of new PISs based on inorganic structures such as polyoxometalates and perovskites. Thus, the possibility to propose new iodonium salts based coumarin could be demonstrated. The best performance was achieved using two-components (PI/Ph2I+) or three-components (PI /Ph2I+/additive) photoinitiating systems under soft irradiation conditions. The kinetics of photopolymerization were evaluated using real time FTIR spectroscopy. The generated radicals were observed using the electron spin resonance (ESR) technique. The laser flash photolysis (LFP) was used as a complementary technique to study the efficiency and the reactivity of radicals generated.

Indiana University-Purdue University Indianapolis (IUPUI) / Hydrogels prepared from photopolymerization have been widely used in many biomedical applications. Ultraviolet (200-400 nm) or visible (400-800 nm) light can interact with light-sensitive compounds called photoinitiators to form radical species that trigger photopolylmerization. Since UV light has potential to cause cell damage, visible light-mediated photopolymerization has attracted much attention. The conventional method to fabricate hydrogels under visible light exposure requires usage of co-initiator triethanolamine (TEA) at high concentration (∼200 mM), which reduces cell viability. Therefore, the first objective of this thesis was to develop a new method to form poly(ethylene glycol)-diacrylate (PEGDA) hydrogel without using TEA. Specifically, thiol-containing molecules (e.g. dithiothreitol or cysteine-containing peptides) were used to replace TEA as both co-initiator and crosslinker. Co-monomer 1-vinyl-2-pyrrolidinone (NVP) was used to accelerate gelation kinetics. The gelation rate could be tuned by changing the concentration of eosinY or NVP. Variation of thiol concentration affected degradation rate of hydrogels. Many bioactive motifs have been immobilized into hydrogels to enhance cell attachment and adhesion in previous studies. In this thesis, pendant peptide RGDS was incorporated via two methods with high incorporation efficiency. The stiffness of hydrogels decreased when incorporating RGDS. The second objective of this thesis was to fabricate hydrogels using poly(ethylene glycol)-tetra-acrylate (PEG4A) macromer instead of PEGDA via the same step-and-chain-growth mixed mode mechanism. Formation of hydrogels using PEGDA in this thesis required high concentration of macromer (∼10 wt.%). Since PEG4A had two more functional acrylate groups than PEGDA, hydrogels could be fabricated using lower concentration of PEG4A (∼4 wt.%). The effects of NVP concentration and thiol content on hydrogel properties were similar to those on PEGDA hydrogels. In addition, the functionality and chemistry of thiol could also affect hydrogel properties.

Master of Science / Department of Grain Science and Industry / Xiuzhi Susan Sun / Soybean oil-based resin for transparent flexible coating applications were formulated by dihydroxyl soybean oil (DSO) with commercial epoxy monomers (i.e., epoxidized soybean oil (ESO) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECHM)). The resin was formed to thermoset polymers using cationic ring-opening photopolymerization. The ether crosslinking and post-polymerization of the polymeric network were observed using Fourier transform infrared spectroscopy. Thermal properties of the bio-based coating materials and their copolymerization behaviors were examined using a differential scanning calorimetry and a thermogravimetric analyzer. Crosslink density and molecular weight between crosslink were obtained from dynamic mechanical analysis. ECHM/DSO (1: 1.43 weight ratio) films showed the highest elongation at break (49.2 %) with a tensile strength of 13.7 MPa. After 2 months storage, the elongation at break and tensile strength of films were 32 % and 15.1 MPa, respectively. ESO/DSO films (w/w ratios of 1:0.1, 1:0.15, and 1:0.2) exhibited stable flexibility around 11-13 % of elongations at break without significant reductions of tensile strengths (2.5 to 4.4 MPa) during 2-months shelf life. Optical transparencies of the films were comparable to commercial glass and polymers, and water uptake properties (0.72 and 2.83%) were significantly low.

Aerogel materials have had limited utility due to their fragility, geometrical limitations, fabrication costs and protracted fabrication times. The objective of this project was to eliminate these limitations. Native, cross-linked and hybrid aerogel monoliths have been fabricated using a newly developed one-pot method without the need for solvent exchange. The key to this technique is the use of an ethanol–water azeotrope mixture, which contains 4.4% water by volume, as both a gelation and supercritical drying solvent. The small water content allows for drying at temperatures close to the supercritical temperature of the dry solvent, where reactions such as silica dissolution and polymer degradation are negligible. This improvement on conventional fabrication processes is of particular importance since it decreases the total duration of aerogel fabrication from five days to one day. Cross-linked silica aerogel monoliths were fabricated using one-pot hydrolysis-condensation wet chemistry methods as well as a rapid photogelation method. Both native silica and cross-linked aerogel components were made with a minimum dimension of up to 3.6 cm and in customizable shapes. Fabrication of homogeneous aerogels using these methods required a maximum of one day, as demonstrated in this work. Finally, LEDs and Laser irradiation were both used to selectively embed cross-linked aerogel into a larger native silica component to provide reinforcement and/or a surface which can be used for labeling or affixing the aerogel component to another surface.