Projection Stereolithography (PSL) is an Additive Manufacturing process that digitally patterns light to selectively expose and layer photopolymer into three dimensional objects. Nanomaterials within the photopolymer are therefore embedded inside fabricated objects. Adding varying concentrations of multi-walled carbon nanotubes (MWCNT) to the photopolymer may allow for the engineering of an objects tensile strength and electric conductivity. This research has two goals (i) the fabrication of three-dimensional structures using PSL and (ii) the material characterization of nanocomposite photopolymers. A morphological matrix design tool was developed and used to categorically analyze published PSL systems. These results were used to justifying design tradeoffs during the design and fabricate of a new PSL system. The developed system has 300μm resolution, 45mm x 25mm fabrication area, 0.23mW/cm2 intensity, and 76.2mm per hour vertical build rate. Nanocomposite materials were created by mixing Objet VeroClear FullCure 810 photopolymer with 0.1, 0.2, and 0.5 weight percent MWCNT using non-localized bath sonication. The curing properties of these nanocomposite mixtures were characterized; adding 0.1 weight-percent MWCNT increases the critical exposure by 10.7% and decreases the depth of penetration by 40.1%. The material strength of these nanocomposites were quantified through tensile testing; adding 0.1 weight-percent MWCNT decreases the tensile stress by 45.89%, the tensile strain by 33.33%, and the elastic modulus by 28.01%. Higher concentrations always had exaggerated effects. Electrical conductivity is only measurable for the 0.5 weight-percent nanocomposite with a 8k/mm resistance. The 0.1 weight-percent nanocomposite was used in the PSL system to fabricate a three-dimensional nanocomposite structure. / Master of Science

The goal of this work was to design and build a mask projection microstereolithography (MPμSL) 3D printing system to characterize, process, and quantify the performance of novel photopolymers. MPμSL is an Additive Manufacturing process that uses DLP technology to digitally pattern UV light and selectively cure entire layers of photopolymer resin and fabricate a three dimensional part. For the MPμSL system designed in this body of work, a process was defined to introduce novel photopolymers and characterize their performance. The characterization process first determines the curing characteristics of the photopolymer, namely the Critical Exposure (Ec) and Depth of Penetration (Dp). Performance of the photopolymer is identified via the fabrication of a benchmark test part, designed to determine the minimum feature size, XY plane accuracy, Z-axis minimum feature size, and Z-axis accuracy of each photopolymer with the system. The first characterized photopolymer was poly (propylene glycol) diacrylate, which was used to benchmark the designed MPμSL system. This included the achievable XY resolution (212 micrometers), minimum layer thickness (20 micrometers), vertical build rate (360 layers/hr), and maximum build volume (6x8x36mm3). This system benchmarking process revealed two areas of underperformance when compared to systems of similar design, which lead to the development of the first two research questions: (i) 'How does minimum feature size vary with exposure energy?' and (ii) 'How does Z-axis accuracy vary with increasing Tinuvin 400 concentration in the prepolymer?' The experiment for research question (i) revealed that achievable feature size decreases by 67% with a 420% increase in exposure energy. Introducing 0.25wt% of the photo-inhibitor Tinuvin 400 demonstrated depth of penetration reduction from 398.5 micrometers to 119.7 micrometers. This corresponds to a decrease in Z-axis error from 119% (no Tinuvin 400) to 9% Z-axis error (0.25% Tinuvin 400). Two novel photopolymers were introduced to the system and characterized. Research question (iii) asks 'What are the curing characteristics of Pluronic L-31 how does it perform in the MPμSL system?' while Research Question 4 similarly queries 'What are the curing characteristics of Phosphonium Ionic Liquid and how does it perform in the MPμSL system?' The Pluronic L-31 with 2wt% photo-initiator had an Ec of 17.2 mJ/cm2 and a Dp of 288.8 micrometers, with a minimum feature size of 57.3 ± 5.7 micrometers, with XY plane error of 6% and a Z-axis error of 83%. Phosphonium Ionic Liquid was mixed in various concentrations into two base polymers, Butyl Diacrylate (0% PIL and 10% PIL) and Poly Ethylene Dimethacrylate (5% PIL, 15% PIL, 25% PIL). Introducing PIL into either base polymer caused the Ec to increase in all samples, while there is no significant trend between increasing concentrations of IL in either PEGDMA or BDA and depth of penetration. Any trends previously identified between penetration depth and Z accuracy do not seem to extend from one resin to another. This means that overall, among all resins, depth of penetration is not an accurate way to predict the Z axis accuracy of a part. Furthermore, increasing concentrations of PIL caused increasing % error in both XY plane and Z-axis accuracy . / Master of Science

The curing characteristics of photopolymer resin determine the relationship between the vat polymerization (VP) process parameters and the layer thickness, geometric accuracy, and surface quality of the 3D printed specimen. Dispersing filler material into the photopolymer resin changes its curing characteristics because the filler scatters and absorbs light, which modifies the curing reaction. However, the ability to cure photopolymer resin with high filler volume fraction is important to 3D print material specimens for specific engineering applications, e.g. structural polymer composite materials, electrical and thermal conductive materials, and ceramic materials for biological and high-temperature environments. We methodically measure the curing characteristics of diacrylate/epoxy photopolymer resin with dispersed glass microspheres. The experiments show that the curing depth, degree-of-cure, and surface roughness depend on both the light exposure dose and the filler fraction. We determine that the degree-of-cure increases with increasing filler fraction for constant exposure dose, and approaches 90% with increasing exposure dose, independent of the filler fraction. The geometric accuracy of the 3D printed specimens decreases with increasing exposure dose and with increasing filler volume fraction due to so-called profile broadening. Finally, we show that the average surface roughness of the 3D printed specimens decreases with increasing exposure dose and filler fraction. This work has implications for VP of photopolymer resins with high filler fraction. / Master of Science / Photopolymer resin is a gel-like liquid material that hardens (cures) into solid after absorbing light energy, and such a material is often used in the field of additive manufacturing (3D printing) to create complex geometry. Certain types of filler materials, such as metal powder or carbon fiber, can be added into the photopolymer resin to tailor the material properties, and thus, affects the curing behavior of photopolymer resin mixed with these filler materials. We conducted an experiment to understand how adding glass microspheres to a consumer grade photopolymer resin affects the process of creating 3D objects. This is important in the context of 3D printing engineered composite materials that derive their function from the organization and orientation of filler material in a matrix. To do this, we created many samples in the shape of a "VT" logo using the composite resin we made and measured their thickness (curing depth), degree-of-cure, surface roughness, and geometric accuracy, as a function of the amount of light energy being exposed to the resin (exposure dose) and the amount of the glass filler being added into the resin (filler fraction). We observed that when we increased the amount of light exposure, it resulted specimens that are thicker and more in degree of cure. Adding the glass filler to the liquid had mixed effects on the hardening process, because glass can scatter light and change how light travels within the resin. As a result, the printed objects became less accurate in shape and have smoother surface with increasing exposure dose and filler fraction, because more light is scattered off the designed curing profile and unintentionally cured the surrounding resin.