Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C08: Physics and Chemistry of Polymer 3D PrintingFocus Live
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Sponsoring Units: DPOLY DSOFT GSNP DFD Chair: Jinhye Bae,University of California, San Diego; Anthony Kotula, NIST |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C08.00001: Enhanced dimensional accuracy and impact resistance of 3D printed polymers using core-shell filaments containing high density polyethylene Jia-Ruey Ai, Bryan D Vogt The limitation of using polyolefins in 3D printing results from the deformation of the printed structure caused by volume change during crystallization. We have previously described a route to partially circumvent this structural distortion using structured core-shell filaments with high density polyethylene (HDPE) shell that are printed with materials extrusion (MatEx) 3D printing. This improved performance was hypothesized to be a result of the core polymer acting as a composite reinforcement to inhibit bending from the stresses generated during the crystallization of HDPE. Here, we describe how the core selection influences the dimensional accuracy of the printed part using a shell of HDPE (at 50 vol%) and cores of polycarbonate-based polymer with increment of glass transition temperature (Tg). As might be expected, the highest Tg core material leads to the lowest warpage and provides the best overall dimensional accuracy. However, these differences in dimensional accuracy are strongly dependent on the details of the print shape. Through quantitative layer-by-layer analysis of complex object, we find that under most printing conditions, parts printed with cores of the highest Tg exhibit the lowest deviations. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C08.00002: Simulated extrusion of filaments into support baths Leanne Friedrich, Jonathan E Seppala Embedded direct ink writing, wherein continuous filaments are extruded into a support bath, has enabled the fabrication of soft materials including living cell scaffolds. Inks and support baths have consisted of Newtonian and non-Newtonian fluids, across a wide viscosity range. Additionally, previous works have used both hydrophobic and hydrophilic materials for inks and support baths. In order to guide material selection for more reliable prints, we use numerical simulations in OpenFOAM to directly probe the effects of viscous dissipation, viscoelasticity, and interfacial energy on the three-dimensional shape and position of the printed filament within the support bath. These simulations indicate that when both the ink and support are Newtonian fluids, their surface tension and the ratio of their viscosities control the cross-sectional shape of the filament. Further, surface tension and support viscosity can both be used to suppress Plateau-Rayleigh instabilities. Introducing a Hershel-Bulkley support bath can stabilize a Newtonian filament and improve the positional accuracy of the print, but it can also introduce new cross-sectional shape irregularities. Printing a Herschel-Bulkley filament into a Newtonian support bath can lead to positioning errors. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C08.00003: Simulation of polymer stretch and disentanglement in Fused-Filament Fabrication (FFF) Benjamin Dolata, Peter Olmsted We utilize the RheoTool package in the OpenFOAM toolbox to simulate the viscoelastic flow of polymer deposition in Fused-Filament Fabrication (FFF). FFF is an additive manufacturing technique whereby polymer filaments are feed through a heated printer head to build three-dimensional structures layer-by-layer. Recent work has shown that the weld strength between layers depends on the interdiffusion of entanglements across the interface and residual stresses arising from flow-induced alignment. We simulate flow-induced conformational changes in the polymer molecules in order to determine how processing conditions influence molecular conformations. The evolution of the polymer microstructure (orientation, stretch, and entanglement fraction) is described by coarse-grained, continuum evolution equations, which we solve numerically within the nozzle as well as within the extruded polymer. We examine different constitutive equations for the polymer and find that models where disentanglement arises from affine-stretch of the molecules overpredict disentanglement at high shear rates. We compare our results to prior analytical theory with simplified dynamics. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C08.00004: 3D Printed Absorber for Capturing Chemotherapy Drugs before they Spread through the Body Hee Jeung Oh, Mariam Aboian, Michael Yi, Jacqueline Maslyn, Whitney Loo, Xi Jiang, Dilworth Parkinson, Mark Wilson, Terilyn Moore, Colin Yee, Gregory Robbins, Florian Barth, Joseph DeSimone, Steven Hetts, Nitash Balsara Cancer is becoming the leading cause of death in most developed nations. Despite efforts to develop targeted and personalized cancer therapeutics, dosing of drugs in cancer chemotherapy is limited by systemic toxic side effects. During intra-arterial chemotherapy infusion to a target organ, typically, more than 50-80% of the injected drug is not trapped in the target organ, bypasses the tumor, and causes severe toxicities in distant locations. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C08.00005: 4D Printing of Shape Memory Polymers Kevin Cavicchi, Bangan Peng The combination of shape memory polymers and 3D printing has led to a new technique termed 4D printing where objected are fabricated that exhibit stimuli-responsive, shape-changing behavior. In this talk we will present approaches to 3D print shape memory polymers through digital light processing (DLP) and fused filament fabrication (FFF). In the case of DLP a monomer formulation containing alkyl acrylates and an ion-pair comonomer is free radically polymerized. The reaction induced microphase separation into ionic and non-ionic domains produces an interpenetrating network structure with two different glass transition temperatures, allowing for multiple shape memory processing. In the FFF printing filaments are prepared from shape memory polymer blends of a thermoplastic elastomer and a crystalline small molecule or polymer. The flow and alignment of the polymer chains during filament fabrication and printing improve the resultant shape memory properties material compared to analogous compression molded articles. |
Monday, March 15, 2021 4:00PM - 4:36PM Live |
C08.00006: Material physics and metrology of material extrusion additive manufacturing Invited Speaker: Jonathan E Seppala Material extrusion additive manufacturing covers a small set of processes and a broad set of materials. The two most common versions are fused filament fabrication (FFF), and direct ink write (DIW). Fused filament fabrication, and at large scale, big area additive manufacturing (BAAM), use thermoplastics or thermoplastic composites processed through liquefication followed by solidification to generate 3-dimensional structures. The technique can produce a wide range of components, from medical implants to wind-mill turbine-blade molds. Further, highly-loaded thermoplastics composites can create green bodies, which are post-processed into metallics or ceramics. Unlike fused filament fabrication, direct ink write utilizes a rich set of material physics (yield stress, thixotropy, support-bath, precipitation, and chemical reactions) to produce 3-dimensional structures. Direct ink write has the advantage of finer resolution and more expansive material space, allowing bioprinting, production of tissues scaffolds, and electronic components. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C08.00007: Vat Photopolymerization in a Hybrid Atomic Force Microscope: In situ, Nanoscale Characterization of the Printing Process Callie Higgins, Tobin Brown, Jason Killgore Vat photopolymerization is a powerful additive manufacturing technique that addresses many applications ranging from personalized medicine to mainstream manufacturing. Unfortunately, this printing process introduces micrometer-scale anisotropic inhomogeneities due to the resin absorptivity, diffusivity, reaction kinetics, and swelling during the requisite photoexposure. Previously, it has not been possible to characterize high-resolution mechanical heterogeneity as it develops during the printing process. By combining DLP 3D printing with atomic force microscopy in a hybrid instrument, heterogeneity of a single, in situ printed voxel is characterized. Here, we describe the instrument and demonstrate one of the three modalities for characterizing voxels during and after printing. In sensing Modality I, the mechanical properties of just-printed, resin-immersed voxels are mapped, providing the framework to study the relationships between voxel sizes, print exposure parameters, and voxel-voxel interactions. This mode also affords iterative print fidelity correction using the measured properties to optimize photopatterning. Overall, this instrument equips researchers with a tool to develop rich insight into resin development, process optimization, and fundamental printing limits. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C08.00008: Volumetric 3D printing enabled by triplet fusion upconversion nanocapsules Tracy Schloemer, Samuel Sanders, Mahesh Gangishetty, Daniel Anderson, Michael Seitz, Christopher Stokes, Daniel congreve One way to achieve volumetric 3D printing, where a vat of polymerizable resin is patterned by light in three dimensions, is to use two-photon photopolymerization (2PP). While this approach has its advantages, high energy ultrafast lasers and slow print speeds hinder widespread adoption. Here, we present an analogous process driven by triplet fusion upconversion (UC). To ensure excellent light penetration through the vat of resin with the high sensitizer/annihilator concentrations required, the UC materials are encased in silica to generate robust nanocapsules for suspension in the resin. By pairing UC nanocapsules and commercially available photoinitiators and resins, we rapidly generate macroscale prints with fine detail. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C08.00009: Triplet-triplet annihilation polymerization (TTAP) for high resolution 3D printing David Limberg, Ji-Hwan Kang, Ryan Hayward Two-photon polymerization (TPP) is currently the dominant approach to 3D printing with very high spatial resolution, down to ~ 100 nm, but suffers from very limited volumetric write speeds compared to conventional stereolithography (SLA) approaches and requires a specialized high intensity pulsed laser source. Here, we demonstrate a new method of photosensitized 3D printing initiated through triplet-triplet-annihilation (TTA) energy upconversion that achieves sub-micron resolution with an LED light source, requiring six orders of magnitude less intense light than TPP. TTA limits polymerization to the focal point of light, and resolution can be modulated from 0.6 μm to over 4 μm thanks to a micromirror array, which also offers the potential for parallelization and high throughput printing. We demonstrate a unique 3D printing mechanism capable of fabricating sub-micron features, and present a model for the system combining established kinetics for TTA and photopolymerization, which provides insight into the mechanism and guides the choice of printing parameters. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C08.00010: Depth-Of-Cure Study and Printing Resolution Analysis of Stereolithography 3D Printing Resins Keith David DeNivo, Anna Marie Smallwood, Alena Nicole Pursel, Patrick Gloria, Chang Ryu Stereolithography (SLA) is a 3D printing method of polymer resins using photoinitiated polymerization. We have studied how the photopolymerization characteristics of SLA photocurable resins affect the 3D printing resolution and mechanical properties. The characteristics include the depth-dependent UV polymerization kinetics. In particular, real time FTIR (RT-FTIR) with attenuated total reflectance (ATR) sample stage was used to study the UV penetration depth effects on the photopolymerization kinetics in terms of the rate of polymerization and monomer conversion at different UV irradiation times and intensities. Three types of commercially available FormLab SLA resins are compared for the study of printing resolution and depth-of-cure characteristics. Additional tuning of depth-of-cure characteristics has been performed by mixing additional photoinitiators or inhibitors. Post UV-curing on the 3D printed samples is performed to further manipulate their mechanical properties with an aim to elucidate how the network structure in SLA samples affect the stress-strain behavior of thermosets under tensile elongation. The layer curing process and morphology has been also investigated by DSC and microscopy. |
Monday, March 15, 2021 5:24PM - 6:00PM Live |
C08.00011: Chemical and Engineering Approaches for Soft Material Additive Manufacturing Invited Speaker: Andrew Boydston Our research team focuses on discovering and developing new chemical approaches and engineering techniques for additive manufacturing. We place emphasis on: 1) incorporation of functional materials, particularly those that respond via conversion of mechanical force into chemical reactivity; 2) expansion of the materials space available for AM; 3) selective multi-material printing from “all-in-one” mixed-resin vats; and 4) unique methods for energy transduction that are atypical in additive manufacturing. As representative examples, we will discuss two unique approaches for additive manufacturing with silicone resins. In each example, we aim for complete geometric freedom as one would enjoy from vat photopolymerization or material fusion techniques, yet neither of our approaches use any photochemical or powder bed technologies. In one discovery, we realized that heating at a patterned photothermal interface (HAPPI) additive manufacturing could be achieved using near-IR light sources in combination with photothermal vat materials. In this way, we were able to construct 3D objects using patterned light while relying on thermal curing of traditional silicone resins. The preliminary mechanical properties of printed parts after thermal post-treatment are on par with those of molded parts. Separately, we discovered that high-intensity focused ultrasound can be used as a method for converting liquid silicone resins into cured 3D object, even through optically opaque barriers. |
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