Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C52: Physics of 3D Printing and Additive ManufacturingFocus
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Sponsoring Units: DPOLY GSOFT Chair: Bryan Vogt, Univ of Akron Room: LACC 512 |
Monday, March 5, 2018 2:30PM - 2:42PM |
C52.00001: A Polymer Science Perspective on Improving Additive Manufacturing Connor Perryman, Sahar Rostom, Neiko Levenhagen, Mark Dadmun 3-D printing of polymers has become an important manufacturing process in industry and among hobbyists. This process, however, results in significantly weak interfaces between filaments and between layers. These weak interfaces manifest in anisotropic properties, where the sample is stronger parallel to the print direction than perpendicular to it. Our research is focused on cultivating methods to understand the adhesion between layers on a molecular level and develop materials and processes to optimize this bonding process and structural robustness. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C52.00002: Chain alignment and welding of polymer interfaces Marco Galvani, Thomas O'Connor, Mark Robbins Fused Filament Fabrication (FFF) is an increasingly popular method for manufacturing of materials. In FFF, layers of polymer are extruded from a nozzle on top of previously deposited layers and bond to them by interdiffusion and formation of entanglements across the interface. The extrusion process in FFF is usually fast enough to align the polymer chains, giving rise to non-equilibrium effects that may alter the entanglement structure at the weld. We perform large scale molecular dynamics simulations of polymer welding. Melts of bead-spring FENE chains in equilibrium or after alignment under simple shear are joined and allowed to interdiffuse. We examine how chain retraction and entanglement evolution affect interdiffusion. After welding, we quench the system below the glass transition temperature and simulate tensile fracture, characterizing craze formation in the materials and strength of the interface for different welding times and degrees of alignment. The results provide insight into the molecular mechanisms responsible for fracture in polymer glasses with aligned chains, relating the degree of alignment to the competition between chain pullout and scission. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C52.00003: Weld formation during material extrusion additive manufacturing Jon Seppala, Sung Hoon Han, Kaitlyn Hillgartner, Chelsea Davis, Kalman Migler Material extrusion (ME) is a layer-by-layer additive manufacturing process that is now used in personal and commercial production where prototyping and customization are required. However, parts produced from ME frequently exhibit poor mechanical performance relative to those from traditional means; moreover, fundamental knowledge of the factors leading to development of inter-layer strength in this highly nonisothermal process is limited. In this work, we seek to understand the development of inter-layer weld strength from the perspective of polymer interdiffusion under conditions of rapidly changing mobility. Our framework centers around three interrelated components: in situ thermal measurements (via infrared imaging), temperature dependent molecular processes (via rheology), and mechanical testing (via mode III fracture). We develop the concept of an equivalent isothermal weld time and test its relationship to fracture energy. For the printing conditions studied the equivalent isothermal weld time for Tref = 230 °C ranged from 0.1 ms to 100 ms. The results of these analysis provide a basis for optimizing inter-layer strength, the limitations of the ME process, and guide development of new materials. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C52.00004: Spectral Analysis for Resonant Soft X-ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures Thomas Ferron, Michael Pope, Brian Collins Interfaces are of critical importance in a wide range of soft matter applications. Progress in organic electronics, bio-interfacing, directed self-assembly, among others require advanced morphological probes to gain critical insight to buried, often 3D, structures and interfaces. Traditional techniques such as electron microscopy, X-ray or neutron scattering are often hampered by minimal density contrast, low levels of crystallinity, or require laborious and potentially disruptive labeling (e.g. deuteration for neutrons). Advances in resonant soft X-ray scattering have shown sensitivity to nano-to-mesoscale structure in polymer blends as well as correlative local measurements of molecular orientation, but thus far such measurements have only been qualitative. Here we demonstrate a quantitative spectral analysis of resonant soft X-ray scattering to measure the volume of buried nonplanar polymer interfaces. We measure the scattering invariant on an absolute scale to quantify the nonplanar interfacial width of 3D block copolymer nanostructures. Using continuous contrast tuning available over an absorption edge, this spectral analysis enables the identification and characterization of potentially limitless unique molecular species in complex nanostructures. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C52.00005: Utilizing Surface Segregating Additives to Improve the Isotropy of Fused Deposition Modeling Products Neiko Levenhagen, Mark Dadmun Reducing the anisotropy of 3D printed parts prepared by fused deposition modeling (FDM) is a major goal for researchers in the 3D printing community. For typical FDM parts, mechanical properties observed of samples printed orthogonal to the print bed (transverse) are significantly weaker than those printed parallel to the bed (longitudinal). These anisotropic properties arise due to limited diffusion and entanglement of chains across the inter-layer interface. Minimizing the anisotropy has been achieved in our group by implementing a process in which bimodal blends comprised of a parent, high molecular weight polymer blended with a chemically identical but low molecular weight (LMW) polymer is utilized. Recently, we have extended this research to include LMW additives with various architectures. For linear and 3-arm star type additives, drastic improvements in the mechanical properties are observed in the transverse orientation; however, not for 4-arm star type additives. To better understand these differences, we compare the effect of additive architecture on the layer adhesion of FDM printed parts and their rheology, from which, we provide crucial insight into the mechanism by which the LMW additives improve the interlayer adhesion. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C52.00006: Computer Simulations of Continuous 3-D Printing Zilu Wang, Heyi Liang, Andrey Dobrynin 3-D printing is a revolutionary manufacturing technique which makes it possible to fabricate objects of any shape and size that are hard to reproduce by traditional methods. We develop a coarse-grained molecular dynamics simulation approach to model the continuous liquid interface production (CLIP) 3-D printing technique. This technique utilizes a continuous polymerization and cross-linking of the liquid monomeric precursor by the UV light within a thin layer while pulling the cross-linked polymeric object out of a pool of monomers. Simulations show that the quality of the shape of the 3-D printed objects is determined by a fine interplay between elastic, capillary, and friction forces. Using simulation results, we identify the source of the object shape deformations and develop a set of rules for calibration of the parameters to meet the accuracy requirements. Comparison between different continuous 3-D printing setups shows that proposed modifications of the printing process could improve quality and accuracy of the printed parts. |
Monday, March 5, 2018 3:42PM - 4:18PM |
C52.00007: Molecules to Manufacturing: Advancing the Polymeric Materials Toolbox for Additive Manufacturing Invited Speaker: Christopher Williams This abstract not available. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C52.00008: Process line measurements of polycaprolactone crystallization in additive manufacturing Anthony Kotula, Lily Northcutt, Kalman Migler Polycaprolactone is a semicrystalline polyester used in additive manufacturing processes for biomaterials. Filament-based additive manufacturing processes often force molten polymer through a printer nozzle at high (> 100 s-1) wall shear rates prior to cooling and crystallization. Although the phenomenon of flow-induced crystallization is well-known, the effect of flow on the crystallization kinetics of polymers is unknown for additive manufacturing. A significant barrier to understanding this process is the lack of in situ measurement techniques to quantify crystallinity after polymer filament extrusion. To address this issue, we use a fiber optic probe to measure the Raman spectrum of extruded polycaprolactone during additive manufacturing. We quantify crystallinity as a function of time for the nozzle temperatures and filament feed rates accessible to the apparatus. Crystallization is shown to occur faster at higher shear rates and lower nozzle temperatures. Our measurements provide experimental evidence of the effect of shear flow on polymer crystallization in additive manufacturing. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C52.00009: Tough, High Impact Resistant 3D Printed Objects from Core-Shell Filaments Fang Peng, Miko Cakmak, Bryan Vogt Fused deposition modeling (FDM), an extrusion-based 3D printing method, uses solid polymeric filaments. Typically, the polymers are formulated to provide desired characteristics and extruded into homogeneous filaments with well-defined diameter. However, an intrinsic weakness of FDM is the poor adhesion between printed layers with the bonding interfaces being poorly developed during printing. These poorly constructed interfaces lead to poor mechanical properties from FDM. Here, we propose a route to attack this intrinsic problem using core-shell structured filaments. The shell polymer is an ionomer and the core is polycarbonate (PC). The disparate solidification temperatures lead to the PC solidifying first to act as fiber reinforcement for shape control, while the ionomer generates a strong shell-shell interface between adjacent filaments. Samples printed from core-shell filaments show enhanced mechanical strength with samples that do not fail and an order of magnitude improvements in impact resistance. The mechanism for improvement is core-shell delamination energy dissipation, which is critical for inhibition of crack propagation. In addition to improvements in mechanical properties, the printed core-shell sample are less prone to warpage than the individual components. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C52.00010: 3D Printing and Evaluation of Novel Nano-graphene Containing ABS Thermoplastics Robert Bubeck, Michael Most, Tracy Zhang Novel Acrylonitrile Butadiene Styrene (ABS) materials melt-blended with 5 wt.% and 10 wt.% XGnP™ M5 graphene nanoplatelets were fabricated into 1.75 mm diameter filament for 3D printing in order to ascertain how strength and toughness of 3D-printed ABS may be affected by M5 addition. Compared to the unmodified ABS, 3D- printed ABS composites containing M5 were determined to have roughly twice the modulus without an unacceptable decrease in toughness. Samples were characterized for molecular weight, AN level, rubber content, and melt rheology. Material and 3D printing variables were assessed. 3D printing patterns (0/90 and 45/45) were selected in order to determine their influences on toughness, tensile and dynamic mechanical properties. Test bars fabricated to shape by 3D printing were compared with analogous bars milled to the identical shape to measure the differences in the resulting physical properties. Generally, the properties for the as-printed tensile samples were found to be inferior to the milled equivalents. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C52.00011: Composite Ink Extrusion Behaviors in Direct Ink Writing with Acoustic Focusing Leanne Friedrich, Matthew Begley Intra-nozzle microparticle positioning methods can impose structural and functional gradients in 3D printed components. One such method is direct ink writing with acoustic focusing (DIWA), wherein a polymer fluid with suspended microparticles flows through a microfluidics channel. A piezoelectric actuator establishes a standing wave in the channel, which co-orients and directs particles to the wave nodes. Using the channel as a direct-write nozzle, we can print filaments with controlled spatial particle distributions. Because drag inhibits acoustic focusing, DIWA inks must be less viscous than conventional direct write inks. In this previously unexplored viscosity domain, we experimentally characterize how surface energies and viscous dissipation influence internal and external filament deformation, which indicate the quality and reliability of DIWA extrusion. Using digital image analysis to measure dynamic contact line positions, filament curvatures, and particle movement, we quantify nozzle wetting, filament stability, and maintenance of spatial particle distributions. By mapping these metrics across extrusion and raster speeds, we measure how the boundaries of the printable region vary in terms of ink composition, nozzle and substrate surface energies, and process parameters. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C52.00012: Soft Matter Manufacturing: 3D Printing with Cells, Gels, Elastomers and Colloids Tapomoy Bhattacharjee, Christopher O'Bryan, Sarah Ellison, Cameron Morley, Samantha Marshall, Thomas Angelini 3D printing is generally a race against instabilities; the challenge is to prevent printed liquid features from moving once deposited. Printing directly into a support material made from jammed granular-scale gel particles mitigates the two nearly ubiquitous sources of instability encountered in 3D printing: surface tension and body forces. Jammed microgels yield at extremely low applied stresses, making them an excellent medium in which to create macroscopic structures with microscopic precision. While tracing out spatial paths with an injection tip, these granular gels yield at the point of injection and then rapidly solidify, trapping injected material in place. In this talk, we demonstrate how this physical approach to creating 3D structures negates the effects of surface tension and gravity, allowing a wide breadth of materials to be structured. With this method we create complex 3D objects made from silicones, hydrogels, colloids, and living cells, including funcitonal living cell constructs and fluidic devices made from silicone. Immediate application areas include tissue engineering, flexible electronics, particle engineering, smart materials, and encapsulation technologies. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C52.00013: Micro 3D Printing of a Temperature-Responsive Hydrogel and Its Applications Daehoon Han, Zhaocheng Lu, Shawn Chester, Howon Lee Poly(N-isopropylacrylamide) (PNIPAAm) has been extensively studied due to its unique thermo-responsive swelling behavior. However, potential of PNIPAAm has not been fully unleashed due to the limited available fabrication processes such as molding and lithographical techniques, which are often inherently 2D in nature. 3D PNIPAAm structures have been achieved employing an origami approach, but accessible 3D geometries are still limited. |
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