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Synthèse de nanoparticules par polymérisation radicalaire en émulsion pour le développement d’une nouvelle phase stationnaire dans des microsystèmes en copolymère d’oléfine cyclique / Synthesis of nanoparticles by emulsion radical polymerization for the development of a new stationary phase in cyclic olefin copolymer microchipsSaadé, Josiane 25 November 2015 (has links)
L’objectif de cette thèse est de synthétiser des nanoparticules dans des microsystèmes en copolymère d’oléfine cyclique (COC), en vue du développement d’une nouvelle phase stationnaire de chromatographie présentant des performances améliorées. Dans un premier temps, la base théorique du projet est présentée. Les performances chromatographiques d’une colonne en fonction de la taille des particules qui la constituent sont présentées, en termes de résolution et d’efficacité, ainsi qu’en temps d’analyse. L’utilisation de nanoparticules s’avère optimale, mais l’état de l’art sur les différents types de colonnes et de modes de séparations en microsystèmes montre la difficulté technique de cet objectif. Les différentes voies de synthèse de nanoparticules par polymérisation radicalaire en micro et miniémulsion sont ensuite détaillées. Les essais préliminaires ont permis de définir la méthodologie d’approche : 1) la synthèse de nanoparticules par polymérisation radicalaire en miniémulsion et 2) la fonctionnalisation indispensable des supports COC. Dans un premier temps, la composition de la miniémulsion a été optimisée par plan d’expériences. La meilleure formulation permet la synthèse, après photopolymérisation, de nanoparticules monodisperses de diamètre moyen inférieur à 200 nm. Une étude d’ancrage des nanoparticules sur plaques COC est ensuite réalisée. L’optimisation du greffage d’un monomère polyéthylène glycol diacrylate (PEGDA) est réalisée par plan d’expériences. La synthèse photochimique des nanoparticules sur des surfaces COC fonctionnalisées PEGDA permet l’obtention de nanoparticules sphériques et monodisperses de taille inférieure à 200 nm répondant parfaitement au cahier des charges. Ce travail constitue une première étape dans la réalisation de phases stationnaires innovantes en chromatographie / The aim of this thesis is the synthesis of nanoparticles in cyclic olefin copolymer (COC) microchips in order to develop a new stationary phase. The bibliography review reveals the interest of this project in increasing column performance (efficiency and resolution) and reducing the analysis time. A general review on stationary phases and separation mode in microchips is presented. The synthesis of nanoparticles by radical polymerization of micro and miniemulsion is then detailed. The preliminary results helped defining the methodological approach: 1) Synthesis of nanoparticles via miniemulsion radical polymerization and 2) functionalization of COC surfaces. First, miniemulsion composition is optimized by an experimental design. The optimal miniemulsion led, after photopolymerization, to monodisperse nanoparticles with a diameter size inferior to 200 nm. The anchorage on COC surface is then investigated and shows that COC functionalization with a hydrophilic monomer is essential. Photografting of polyethylene glycol methacrylate (PEGDA) optimization is carried out by an experimental design. The UV synthesis of nanoparticles on COC surfaces functionalized by PEGDA is demonstrated. Monodisperse and spherical nanoparticles with a diameter size inferior to 200 nm are obtained. This work is considered as a first step in the development of a new stationary phase for chromatography
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Advances In light-induced polymerizations: I. Shadow cure in free radical photopolymerizations, II. Experimental and modeling studies of photoinitiator systems for effective polymerizations with LEDsKitano, Hajime 01 July 2012 (has links)
Photopolymerization has become the standard for many coating and printing applications that require rapid curing at room temperature due to its potential to reduce volatile organic compound (VOC) emissions while providing a means for efficient manufacturing processes. These advantages could be useful in a variety of emerging applications, such as anisotropic conductive films (ACF) if photopolymerization could extend into relatively narrow shadow regions which are not directly illuminated, and if visible wavelengths that are not absorbed by polyimide films could be used to trigger the reaction.
The broad objectives of this research are i) to examine the factors that determine the attainable extent of shadow cure in free radical polymerizations, and ii) to develop initiator systems effective for polymerization using visible light and light emitting diode (LED) lamps.
Project I: Shadow Cure in Free Radical Photopolymerizations
In this project, the extent of shadow cure in visible-light-induced free radical photopolymerization is investigated. A number of effective methods such as adding additives, utilizing a reflective stage, and increasing the light intensity are introduced. In addition, the use of fluorescent dyes in multi-component photoinitiator systems proved to be very effective for shadow cure because the fluorescent light emitted from the dye could irradiate the shadow region.
When considering practical resins, mixtures of oligomers and monomers, the viscosity is the major barrier that must be overcome in order to achieve high conversion in the shadow regions using visible-light-induced multi-component photoinitiator systems. Hence, instead of using multi-component systems, a commercial visible-light-induced single-component photoinitiator is investigated. As a result, a high conversion in shadow regions of the viscous oligomer containing resin is achieved.
Project II: Experimental and Modeling Studies of Photoinitiator Systems for Effective Polymerizations with LEDs
In this project, various LED photocuring systems are investigated and characterized. The light intensities of LEDs become weaker as their peak emission wavelengths decrease. Therefore, to design the practical process of LED curing, the effect of both the light intensity and the emission spectrum of the lamp must be considered. Photopolymerization for four representative UV photoinitiators with different LEDs are investigated experimentally and theoretically. The effective light source is dependent on the photoinitiators and several LEDs demonstrate high thin cure ability. The calculated results from a model display good qualitative correspondence with the experimental results. Various interesting suggestions are obtained using this model. For example, the commercialization of 355 nm LEDs might be able to superior photopolymerization compared to other currently available LED lamps.
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Tepelná stabilita/degradace vysokoviskózních dentálních pryskyřic / Thermal Stability/Degradation of High Viscosity Dental ResinsBystřický, Zdeněk January 2012 (has links)
This diploma thesis deals with the influence of long term thermal load on the stability of high-viscous resins used for dental composites matrix. The process of polymerization was also investigated in connection with type and ratio of monomer units, mass content of the initiator system and the presence of nanosilica filler. Prepared resins were characterized by differential compensation photocalorimetry (DPC) and dynamic mechanical analysis (DMA). The dependence of the heat flow on time was measured by DPC. Based on the experimental data, the dependence of conversion on time and the dependence of polymerization rate on conversion were determined. Viscoelastic properties of the cured resins were determined by DMA. Experimentally measured data implies that by the influence of elevated temperature both the degree of conversion and the polymerization rate decreased. With a higher content of the initiator system incorporated in resin the decrease was more significant. Therefore, we can conclude that when the resin was exposed to the elevated temperature one of the components of the initiator system was inactivated. For the photopolymerized resins presence of two glass transition temperatures is typical due to the inhomogenous morphology of the cured resin. There are two types of domains with varying relative composition. However, after the degradation only one glass transition temperature was detected. That was caused by reducing the resin viscosity due to the increased temperature. Higher mobility of the initiator system molecules and monomers itself resulted in more homogenous structure of the cured resin. In case of elevated temperature exposed resins more significant decrease of the elastic modulus was observed. The curing process is considerably influenced by the type and ratio of the monomer units and by the presence of filler.
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Optimisation du procédé de photopolymérisation pour l'élaboration de matériaux composites épais à matrice époxyde. / Optimization of the photopolymerization process for the elaboration of thick epoxy composite materialsIbanez, Cyrielle 22 November 2019 (has links)
Le procédé de photopolymérisation a été optimisé en vue de l’élaboration de matériaux composites à matrice époxyde épais (> 1 mm) via un mécanisme cationique. L’étude des cinétiques de photopolymérisation de deux résines époxydes (glycidyl éther et cycloaliphatique) a montré que l’ajout d’un renfort de microsphères de silice induit un gradient de conversion dans l’épaisseur du matériau en raison d’un phénomène d’absorption et/ou de diffusion de la lumière, ce dernier étant d’autant plus important que l’écart d’indice de réfraction entre la charge et la matrice est élevé. Cependant, cette hétérogénéité de conversion a pu être compensée par une réaction de postpolymérisation à température ambiante. Une analyse des propriétés mécaniques a ensuite montré qu’il est possible d’obtenir par photopolymérisation des matériaux composites épais réticulés de façon homogène et dont la rigidité est augmentée par la présence du renfort. Enfin, la stratégie d’égalisation des indices de réfraction de la charge et de la matrice, couplée à une photopolymérisation cationique frontale induite par voie radicalaire (RICFP), ouvre des perspectives intéressantes en vue de l’élaboration de photocomposites de plusieurs centimètres d’épaisseur en appliquant uniquement un stimulus lumineux. / The photopolymerization process has been optimized for the elaboration of thick epoxy composite materials (> 1 mm) through a cationic mechanism. The study of the photopolymerization kinetics of two epoxy resins (glycidyl ether and cycloaliphatic) has shown that the addition of a silica microsphere reinforcement induced conversion gradient in the material thickness, resulting from a light absorption and/or scattering phenomenon. The light scattering is all the more important as the refractive index gap between filler and matrix is high. However, this conversion heterogeneity has been compensated by a postpolymerization reaction at room temperature. Then, the analysis of the mechanical properties has shown that it was possible to obtain thick composite materials homogeneously crosslinked and whose rigidity was increased by the presence of the filler. In addition, the strategy of equalizing the filler and matrix refractive indices, coupled with the radical induced cationic frontal polymerization (RICFP) opens interesting perspectives for the development of photocomposites several centimeters thick using only a light stimulus.
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Polymérisation cationique photo-thermique de résines époxydes / Photo- and thermal cationic polymerization of epoxidesMarechal, David 22 October 2013 (has links)
Le groupe Mäder s’est lancé depuis quelques années dans une nouvelle thématique, la polymérisation « dual-cure ». Il s’agit d’un processus photo-thermique couplant réactivité photochimique et thermique. Cette thématique vise des applications pour lesquelles le produit est épais et/ou fortement chargé. La photopolymérisation étant limitée en profondeur, le processus thermique permet de compléter la polymérisation au coeur de l’échantillon ou encore dans les zones non accessibles par la technologie UV/LED. Cette thématique a fait l’œuvre d’une première thèse (2007-2010) menée par le doctorant Adrien Criqui au sein du Département de Photochimie Général (DPG). Au cours de cette thèse, la polymérisation radicalaire photo-thermique à partir d’aldéhydes a été étudiée. Des résultats concluant ont été obtenus donnant naissance à une technologie innovante notamment avec des applications sous air. Dès lors, il s’est posé la question de savoir si les aldéhydes pouvaient être utilisés dans la polymérisation cationique photo-thermique. La première année de thèse a donc commencé par l’étude du potentiel des aldéhydes dans la polymérisation cationique photo-thermique de résine époxydes. Les aldéhydes ont montrés qu’ils sont de bons photosensibilisateurs de la photopolymérisation cationique amorcée par un sel d’iodonium. Certaines structures aldéhydes couplées à un sel d’iodonium ont conduit à une polymérisation thermique. Les vitesses de polymérisation sont néanmoins trop lentes pour pouvoir être exploitées. La voie des aldéhydes a donc été abandonnée suite à ces résultats. Malgré ceci, ce sujet a fait l’œuvre d’une étude mécanistique qui a permit de conclure que le couple sel d’iodonium/aldéhyde réagit selon un mécanisme redox au courant duquel l’auto-oxydation de l’aldéhyde est indispensable. La réduction du photoamorceur par le radical issu de l’auto-oxydation de l’aldéhyde permet d’amorcer la polymérisation cationique. Par la suite, une importante bibliographie sur la polymérisation cationique des époxydes a été réalisée, le but étant de rechercher de nouveaux systèmes amorceurs. Plusieurs systèmes ont alors été retenus à savoir, les acides de Lewis et de Brönsted ainsi que les espèces cationiques. Les acides de Lewis étudiés n’ont pas apportés de résultats satisfaisants et ont donc été abandonnés. Parmi les acides de Brönsted, les acides sulfoniques ont été sélectionné. Des résultats mitigés ont été obtenus. En effet, soit la polymérisation s’est montrée trop rapide et non contrôlable soit trop lente. Le mécanisme de polymérisation amorcé par ces espèces ne semble pas adapté aux résines époxydes. La synthèse d’une structure appropriée a été envisagée mais pour des raisons stratégiques a été par la suite abandonnée. Plusieurs structures d’espèces cationiques ont été étudiées, à la fois des espèces commerciales (ex : triphénylcarbénium, …) ainsi que des espèces synthétisées au laboratoire (ex : xanthénium, …). Les travaux effectués sur ces systèmes amorceurs ont montrés qu’un amorçage indirect avec formation de l’amorceur in situ était une voie à privilégier.A partir de ce constat, deux technologies ont été étudiées. La première, à caractère purement académique, concerne une voie redox. Un système déjà publié basé sur le système sel d’iodonium/sel de cuivre/acétoïne a été ré-évalué. Les résultats obtenus ne correspondant pas au mécanisme publié, une étude mécanistique a été réalisée afin de proposer un nouveau mécanisme réactionnel. Le mécanisme de réaction est basé sur une réaction de décomposition, probablement par complexation, du sel d’iodonium par un sel de cuivre. Le produit de décomposition formé étant sensible à l’hydrolyse, il est possible d’accélérer la vitesse de polymérisation par la présence d’un composé hydroxylé type acétoïne. [...] / In the past few years, The Mäder Group has launched a new theme, " dual- cure " polymerization and process. This process is a coupling between photochemical and thermal reactivity. This theme is designed for applications where the product is thick and/or loaded with fillers. The photopolymerization is limited in depth and then the thermal process is used to complete the polymerization of the sample or in the non-irradiated areas. This theme has been the work of a first PhD (2007-2010) conducted by the student Adrien Criqui in the “Département de Photochimie Générale (DPG)”. In this PhD, the photo- and thermal radical polymerization with aldehydes was studied. Results have given birth to an innovative technology, particularly with applications under air. Therefore, it wonder if aldehydes could be used in the photo- and thermal cationic polymerization.The first year of PhD has begun with the study of the potential of aldehydes in the photo- and thermal cationic polymerization of epoxy resin. Aldehydes have shown that they are good photosensitizers of the cationic photopolymerization initiated by an iodonium salt. Some aldehydes coupled with an iodonium salt led to thermal polymerization. However rates of polymerization are too slow to be exploited. The way of aldehydes has been aborted due to these results. Despite this, this topic has been the work of a mechanistic study that led to the conclusion that the iodonium/aldehyde salt couple reacts according to a redox mechanism in which the auto-oxidation of the aldehyde is essential. The reduction of the photoinitiator by the radical derived from the auto- oxidation of the aldehyde aollow to initiate cationic polymerization.Subsequently, an extensive bibliography on the cationic polymerization of epoxides was carried out with the aim to find new initiator systems. Therefore, several systems have been selected i.e., Lewis and Brösted acids, and cationic species. Lewis acids studied gave no satisfactory results and were therefore given up. Among the Bronsted acids, sulfonic acids were selected. Mixed results were obtained. Sometimes the polymerization has been too fast and sometimes too slow. The polymerization mechanism initiated by these species does not seem suitable for epoxy resins. The synthesis of a suitable sulfonic acid was considered but for strategic reasons was later dropped. Several structures of cationic species have been also studied, both commercial species (eg: triphenylcarbenium , ... ) as well as synthesized species (eg: xanthénium ...). Work on these initiator systems convinced to use an indirect method to initiate polymerization.From this, two technologies have been studied. The first, relates to a redox pathway. A published system based on iodonium salt/copper salt/acetoïne combination has been re-evaluated. Results do not match the published mechanism. A new mechanistic has been proposed. The reaction mechanism is based on a decomposition reaction, presumably by complexation, of the iodonium salt with a copper salt. The decomposition product formed is susceptible to hydrolysis. Rates of polymerization have been accelerated the by the presence of a hydroxy compound like acetoïne. From the knowledges, ways of controlling the rate of polymerization (eg: complexing metal salt) and a new initiator system have been proposed. The second technology relates to a bi-component consisting of a photoinitiator/thermal initiator and a co- initiator. The reaction between the initiator and co-initiator allows initiating the polymerization. The polymerization rate can be controlled from the structure of initiator and co-initiator. The initiator is also a photoinitiator, the photo- and thermal nature is ensured. Two classes of co-initiators have been studied from a fundamental point of view (hydroperoxides and vinyl ether). It has been shown that hydroperoxides reduce initiator by an electron transfer. [...]
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Silk fibroin-reinforced hydrogels for growth factor delivery and In Vitro cell cultureBragg, John Campbell 12 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / A variety of polymers of synthetic origins (e.g., poly(ethylene glycol) or PEG) and naturally derived macromolecules (e.g., silk fibroin or gelatin) have been explored as the backbone materials for hydrogel crosslinking. Purely synthetic hydrogels are usually inert, covalently crosslinked, and have limited degradability unless degradable macromers are synthesized and incorporated into the hydrogel network. Conversely, naturally derived macromers often contain bioactive motifs that can provide biomimicry to the resulting hydrogels. However, hydrogels fabricated from a single macromer often have limitations inherent to the macromer itself. For example, to obtain high modulus PEG-based hydrogels requires an increase in macromer and crosslinker content. This is associated with an increase in radical concentration during polymerization which may cause death of encapsulated cells.
Pure gelatin (G) hydrogels have weak mechanical properties and gelatin undergoes thermo-reversible physical gelation. Covalent crosslinking is usually necessary to produce stable gelatin hydrogels, particularly at physiological temperatures. The limitations of these hydrogels may be circumvented by combining them with another macromer (e.g., silk fibroin) to form hybrid hydrogels. Silk fibroin (SF) from Bombyx mori silkworms offers high mechanical strength, slow enzymatic degradability, and can easily form physical hydrogels.
The first objective of this thesis was to evaluate the effect of sonication and the presence of synthetic polymer (e.g., poly (ethylene glycol) diacrylate or PEGDA) or natural macromer (e.g., gelatin) on SF physical gelation kinetics. SF physical gelation was assessed qualitatively via tilt tests. Gelation of pure SF solutions was compared
to mixtures of SF and PEGDA or G, both with or without sonication of SF prior to mixing. The effect of gelatin on SF gelation was also evaluated quantitatively via real time in situ rheometry. Sonication accelerated gelation of SF from days to hours or minutes depending on SF concentration and sonication intensity. Both PEGDA and G were shown to accelerate SF physical gelation when added to SF and sonicated SF (SSF) solutions.
The second objective was to develop a simple strategy to modulate covalently crosslinked PEG-based hydrogel properties by physically entrapping silk fibroin. The physical entrapment of silk fibroin provides an alternative method to increase gel storage modulus (G’) without the cytotoxic effect of increasing macromer and crosslinker concentration, or altering degradation kinetics by increasing co-monomer concentration. The effect of SF entrapment on gel physical and mechanical properties, as well as hydrolytic degradation and chemical gelation kinetics were characterized. SF physical crosslinking within the PEG-based network was shown to increase gel storage moduli by two days after gel fabrication. There was no change hydrolytic degradation rate associated with the increased moduli. SF entrapment did not affect gelation efficiency, but did alter gel physical properties.
The third objective of this thesis was to develop a silk-gelatin in situ forming hybrid hydrogel for affinity-based growth factor sequestration and release and in vitro cell culture. SF provides mechanical strength and stability, whereas G contains bioactive motifs that can provide biomimicry to the gel network. Hydrogel G’ and its dependency on temperature, SF processing conditions, and secondary in situ chemical crosslinking (i.e., genipin crosslinking) were studied. Gelatin can be conjugated with heparin, a glycosaminoglycan, to impart growth factor (GF) binding affinity. Growth factor sequestration and release were evaluated in a pair of designed experiments. The hybrid gels were evaluated as substrates for human mesenchymal stem cell proliferation.
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PET-RAFT Polymerization: Under Flow Chemistry and Surface Initiated PolymerizationRong, Lihan 27 January 2023 (has links)
No description available.
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Photopolymerization-Induced Crystallization in Relation to Solid-Liquid Phase Diagrams of Blends of Blends of Poly(ethylene oxide)/Multi-functional Acrylate MonomersPark, Soo Jeoung 26 August 2008 (has links)
No description available.
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Photoisomerization - And Photopolymerization-Induced Phase Transitions in Mixtures of Photoresponsive Chromophores and Reactive MesogensKim, Namil 09 August 2010 (has links)
No description available.
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Vat Photopolymerization of High-Performance Materials through Investigation of Crosslinked Network Design and Light Scattering ModelingFeller, Keyton D. 08 June 2023 (has links)
The reliance on low-viscosity and photoactive resins limits the accessible properties for vat photopolymerization (VP) materials required for engineering applications. This has limited the adoption of VP for producing end-use parts, which typically require high MW polymers and/or more stable chemical functionality. Decoupling the viscosity and molecular weight relationship for VP resins has been completed recently for polyimides and highperformance elastomers by photocuring a scaffold around polymer precursors or polymer nanoparticles, respectively. Both of these materials are first shaped by printing a green part followed by thermal post-processing to achieve the final part properties. This dissertation focuses on improving the processability of these material systems by (i) investigating the impact of scaffold architecture and polysalt monomer composition on photocuring, thermal post-processing, and resulting thermomechanical properties and (ii) developing a Monte Carlo ray-tracing (MCRT) simulation to predict light scattering and photocuring behavior in particle-filled resins, specifically zinc oxide nanoparticles in a rigid polyester resin and styrene butadiene rubber latex resin.
The first portion of the dissertation introduces VP of a tetra-acid and half-ester-based polysalt resin derived from 4,4'-oxydiphthalic anhydride and 4,4-oxydianiline (ODPA-ODA), a fully aromatic polyimide with high glass transition temperature and thermal stability. This polyimide, and polyimides like this, find use in demanding industries such as aerospace, automotive and electronic applications. The author evaluated the hypothesis that a non-bound triethylene glycol dimethacrylate (TEGDMA) scaffold would facilitate more efficient scaffold burnout and thus achieve parts with reduced off-gassing potential at elevated temperatures.
Both resins demonstrated photocuring and were able to print solid and complex latticed parts. When thermally processed to 400 oC, only 3% of the TEGDMA scaffold remained within the final parts. The half-ester resin exhibits higher char yield, resulting from partial degradation of the polyimide backbone, potentially caused by lack of solvent retention limiting the imidization conversion. The tetra-acid exhibits a Tg of 260oC, while the half-ester displays a higher Tg of 380 oC caused by the degradation of the polymer backbone, forming residual char, restricting chain mobility. Solid parts displayed a phase-separated morphology while the half-ester latticed parts appear solid, indicating solvent removal occurs faster in the half-ester composition, presumably due to reduced polar acid functionality. This platform and scaffold architecture enables a modular approach to produce novel and easily customizable UV-curable polyimides to easily increase the variety of polyimides and the accessible properties of printed polyimides through VP.
The second section of this dissertation describes the creation and validation of a MCRT simulation to predict light scattering and the resulting photocured shape of a ZnO-filled resin nanocomposite. Relative to prior MCRT simulations in the literature, this approach requires only simple, easily acquired inputs gathered from dynamic light scattering, refractometry, UV-vis spectroscopy, beam profilometry, and VP working curves to produce 2D exposure distributions. The concentration of 20 nm ZnO varied from 1 to 5 vol% and was exposed to a 7X7 pixel square ( 250 µm) from 5 to 11 s. Compared to experimentally produced cure profiles, the MCRT simulation is shown to predict cure depth within 10% (15 µm) and cure widths within 30% (20 µm), below the controllable resolution of the printer. Despite this success, this study was limited to small particles and low loadings to avoid polycrystalline particles and maintain dispersion stability for the duration of the experiments.
Expanding the MCRT simulation to latex-based resins which are comprised of polymer nanoparticles that are amorphous, homogeneous, and colloidally stable. This allows for validating the MCRT with larger particles (100 nm) at higher loadings. Simulated cure profiles of styrene-butadiene rubber (SBR) loadings from 5 vol% to 25 vol% predicted cure depths within 20% ( µm) and cure widths within 50% ( µm) of experimental values. The error observed within the latex-based resin is significantly higher than in the ZnO resin and potentially caused by the green part shrinking due to evaporation of the resin's water, which leads to errors when trying to experimentally measure the cure profiles.
This dissertation demonstrates the development of novel and functional materials and creation process-related improvements. Specifically, this dissertation presents a materials platform for the future development of unique photocurable engineering polymers and a corresponding physics-based model to aid in processing. / Doctor of Philosophy / Vat Photopolymerization (VP) is a 3D printing process that uses ultraviolet (UV) light to selectively cure liquid photosensitive resin into a solid part in a layer-by-layer fashion. Parts produced with VP exhibit a smooth surface finish and fine features of less than 100 µm (i.e., width of human hair). Recoating the liquid resin for each layer limits VP to low-viscosity resins, thus limiting the molecular weight (and thus performance) of the printed polymers accessible. Materials that are low molecular weight are limited in achieving desirable properties, such as elongation, strength, and heat resistance. Solvent-based resins, such as polysalt and latex resins have demonstrated the ability to decouple the viscosity and molecular weight relationship by eliminating polymer entanglements using low-molecular-weight precursors or isolating high-molecular-weight polymers into particles. This dissertation focuses on expanding and improving the printability of these methods.
The second chapter of the dissertation investigates the impact of scaffold architecture in printing polyimide polysalts to improve scaffold burnout. Polysalts are polymers that exist as dissolved salts in solution, with each monomer holding two electronic charges. When heated, the solvent evaporates and the monomers react to form a high molecular-weight polymer. While previous work featured a polysalt that was covalently bonded to the monomers, the polysalt in this work is made printable by co-dissolving a scaffold. The polysalt resins are photocured and thermally processed to polymerize and imidize into a high-molecular-weight polymer, while simultaneously pyrolyzing the scaffold. Using a co-dissolved scaffold allows the investigation of two different monomers of tetra-acid and half-ester functionality. The half-ester composition underwent degradation during heating, increasing the printed parts' glass transition or softening point. The scaffold had little impact on the polysalt polymerization or final part properties and was efficiently removed, with only 3% remaining in final parts. The composition and properties of the monomers selected played a bigger role due to partial degradation altering the properties of the final parts. Overall, this platform and scaffold architecture allows for a larger number of polyimides to be accessible and easily customizable for future VP demands.
The third chapter describes the challenges of processing photocurable resins that contain particles due to the UV light scattering in the resin vat during printing. When the light from the printer hits a particle, it is scattered in all directions causing the layer shape to be distorted from the designed shape. To overcome this, a Monte Carlo ray-tracing (MCRT) simulation was developed to mimic light rays scattering within the resin vat. The simulation was validated by comparing simulation results against experiment trials of photocuring resins containing 20nm zinc oxide (ZnO) nanoparticles. The MCRT simulation predicted all the experimental cure depths within 10% (20 µm) and cured widths within 30% (15 µm) error.
Despite the high accuracy, this study was limited to small particles and low concentrations.
Simulating larger particles is difficult as the simulation assumes each particle to be uniform throughout its volume, which is atypical of large ceramic particles.
The fourth chapter enables high particle volume loading by using a highly stretchable styrene-butadiene rubber (SBR) latex-based resin. Latex-based resins maintain low viscosity by separating large polymer chains into nano-particles that are noncrystalline and uniform.
When the chains are separated, they cannot interact or entangle, keeping the viscosity low even at high concentrations (>30 vol%). Like the ZnO-filled resin, the latex resin is experimentally cured and the MCRT simulation predicts the resulting cure shape. The MCRT simulation predicted cure depths within 20% (100 µm) and over-cure widths within 50% (100 µm) of experimental values. This error is substantially higher than the ZnO work and is believed to be caused by the water evaporating from the cured resin resulting in inconsistent measurements of the cured dimensions.
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