Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S05: Physics of Soft Materials Advanced Manufacturing I: Extrusion and PerformanceFocus
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Sponsoring Units: DPOLY Chair: Leanne Friedrich, National Institute of Standards and Tech Room: Room 128 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S05.00001: Spatially and temporally resolved crystallization and orientation of high performance polymers during additive manufacturing Invited Speaker: Hilmar Koerner Additive manufacturing of high-performance polymers enables light-weighting for aerospace applications and complexity enabled capabilities for military applications. While good progress has been made towards robust processing, the coupling of processing parameters to morphological evolution and resulting heterogeneities in material properties and their effects on mechanical performance still lacks detailed understanding. Extrusion-based 3D printing of polymers such as PEEK is challenged by fast crystallization kinetics far from equilibrium that lead to challenges in batch repeatability and inconsistencies in performance. Overall, degree of crystallinity and heterogeneities of crystallinity between roads and layers lead to weak mechanical performance. Real-time monitoring techniques, such as synchrotron X-ray scattering experiments, shed light on the evolution of crystallite size, alignment and crystallinity. Real-time wide-angle and small-angle scattering with a microbeam setup and an industrial printhead are used on a 7-axis table to capture temporally and spatially resolved crystallinity, crystallization kinetics and polymer alignment during the 3D printinging process. The result reveals 2D maps of crystallinity and crystallite orientation within roads and at road and layer interfaces. The real-time snapshot over several centimeters along the heated build platform and throughout the height of the printed roads offers never-before-seen details of heterogeneous crystallization kinetics and polymer morphology at interfaces during extrusion-based 3D printing of high-performance polymers and enables a facile way to optimize processing parameters for improved performance of additively manufactured parts. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S05.00002: Additive Manufacturing of Multimaterials with Controllable Microstructure Daniel V Krogstad Additive manufacturing (AM) is a promising approach to fabricate polymer multimaterials for custom actuators. In particular, the use of AM approaches, such as direct ink writing (DIW), allow us to produce these polymer actuators with highly controllable multiscale structure as well as customizable geometries. Here, we will present our work on developing the materials and processes necessary to create multimaterial structures through extrusion-based AM. In one system, we have developed a series of DIW printable epoxy/block copolymer (BCP) blends with controllable microstructures and thus, mechanical properties. Using rheology and small angle x-ray scattering, we have shown that the self-assembled nanostructures within the blends can be controlled by the composition as well as through the non-equilibrium processing conditions that occur during printing. Printing multimaterials with a combination of high stiffness and low stiffness epoxy/BCP materials enables the formation of passive actuators. Mechanical testing with digital image correlation was then used to show that classical lamination theory can be extended to predict the coupled mechanical response of the materials in response to an applied load. This work shows that multimaterial structures with controllable nanostructures can be designed and fabricated, laying the groundwork for the development of future 3D printed multifunctional actuators. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S05.00003: 3D printing of granular microgels: rheological responses with capillary interactions Zhecun Guan, Jinhye Bae Colloids and particle suspensions have served as facile approaches to introduce biological functionalities by loading with bioactive agents. The jamming behaviors of packed granular microgels enable their use as a support medium for 3D printing stable shapes. Unfortunately, the loose interactions among a liquid-particle suspension system result in low self-supporting ability in extrusion-based 3D printing. To address this shortcoming, secondary immiscible liquid is introduced into the system, in which particle networks are formed through the capillary bridges, known as capillary suspensions. Rigid particle systems with capillary suspensions have been widely investigated, however, the rheological response of the capillarity-mediated soft particle networks remains to be elucidated. Here, it is demonstrated that the size and stiffness of soft microgels depend on the emulsification method, and their rheological responses can be manipulated in the presence of capillary bridges. These findings offer an in-depth understanding of how soft, deformable microgels can be munufactured into programmable bulk microstructured materials and how the size of microgels and concentrations of capillary liquid affect the rheological response, thus paving a new way for the adjustment of interparticle interaction in soft particle systems. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S05.00004: Shape Memory Effect of Polymer Composites Dharneedar Ravichandran Shape memory polymers (SMP) are a new class of materials that can recover their shape through an external stimulus and are primarily composed of elastomers, gels, or other soft matter. Reversible one-way shape recovery of these materials for complex geometries can provide control over their dynamic material properties by combining various polymers. Here we present the use of a newly designed and developed 3D printing mechanism, multiphase direct ink writing (MDIW), for the one-step fabrication of layered composite structures with shape memory. The MDIW allows for a combination of a few different polymers and nanoparticles to effectively tune the material properties to precisely control their stimuli responsiveness. The shape memory polymer was composed of thermoplastic polyurethanes (TPUs), biodegradable semi-crystalline polycaprolactone (PCL), and metallic iron oxide (Fe3O4) nanoparticles. The composite was designed to respond to thermal and magnetic stimulus with elastomeric TPUs providing the necessary flexibility and strength, while the PCL was used to tune the thermal responsiveness with its low melting temperature and Fe3O4 for the magnetic responsiveness. The as-fabricated structures displayed actuation control over a wide temperature range of 40 - 65°C and an efficient recovery rate at higher strain loading. The layered arrangement of the polymers displayed recovery of complex shapes and magnetic maneuverability with 5 degrees of freedom. The dimension-temperature-time relationship of the SMP provides a broad application in bioengineering, microfluidics, energy, and aerospace. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S05.00005: Controlling Residual Stress in Material Extrusion Austin W Riggins, Mark D Dadmun Fused filament fabrication (FFF) is a popular method of Material Extrusion additive manufacturing. Semi-crystalline polymers such as poly(lactic acid) (PLA) and poly(ether ether ketone) (PEEK) are easily processed using FFF; however, the slow mobility of polymer molecules, along with a complex thermal history, results in residual stress and limited interfilament diffusion within the printed parts. The impact of graphene incorporation into FFF feedstocks and in situ light-initiated crosslinking on residual stress is examined in this work. Stress release in FFF-printed PLA and PEEK monoliths was monitored over a 24-hour period by measuring their dimensional changes with thermal annealing (irreversible thermal strain). Filament formulation and light irradiation produced varying magnitudes of strain in the annealed monoliths, indicating that the residual stress of FFF-printed structures can be controlled. Differential scanning calorimetry provides evidence that polymer spherulite growth contributes to the irreversible strain; this is particularly important for PEEK, in which crystalline domains act as barriers to diffusion but may grow large enough to produce interlocked filament interfaces. Annealing printed structures with solvent vapors to release internal stress will also be discussed. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S05.00006: Enhanced Structural Stability and Interfacial Strength of Thermoplastic Elastomers using Dual Material Bi-layered Filaments by Material Extrusion Additive Manufacturing Jay H Park, Nikhil Patil, Eric D Wetzel, Kartik H Joshi While fused filament fabrication (FFF) for soft elastic materials has gained interest, critical challenges need to be addressed for 3d-printing such soft materials. Present technologies within FFF yields poor print resolution, inconsistent print parts, and buckling of filament. This investigation focuses on developing structural integrity and mechanical performance of thermoplastic elastomer (TPE) parts by FFF technique. Proposed approach improves 3D printing characteristics of TPE (shore hardness 75A) by assembling smaller volume fractions of ABS material, to develop core-shell structure of ABS and TPE respectively. Rheological characterizations of feed material using high and low shear viscometry provided an insight about optimizing extrusion parameters for filament production as well as wetting characteristic at the printing interface. Structural integrity of produced filaments was verified by fabricating high precision 3D printed complex benchmark geometries. Izod and 3-point bending test's helped verify that filament geometry was significant for enhancing impact resistance and flexibility of the printed part, owing to its superior interlayer adhesion. Higher volume fractions of TPE exhibited better interlayer adhesion, withstanding mechanical strain of 20% due to its interlayer cohesion. Microstructures of printed geometries under microscope verified good print uniformity of 3D-printed structures with high packing density within adjacent layers. Further investigation includes AFM modulus mapping of print structures to micro-analyze flexibility among soft segments. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S05.00007: Reducing Anisotropy in FFF Printed High-Temperature Thermoplastic Polymers: The importance of Crystallization Mark D Dadmun Limiting anisotropy in the design of geometrically complex and 3D printed structures via material extrusion additive manufacturing (or 3D printing) remains a critical issue that hampers the widespread adoption of the technology. Fused filament fabrication (FFF), in particular, is the most widely used 3D printing approach However, due to the complex shear and thermal history that the material experience in the printing process, weak inter-filament bonding ensues due to incomplete polymer diffusion, causing significant mechanical anisotropy in the final parts. To improve this interfacial adhesion and tailor polymer diffusion, our research group has previously incorporated low-molecular-weight (LMW) additives into poly(lactic acid) (PLA) and acrylonitrile butadiene styrene (ABS) polymer blends that surface segregate which improves interfacial adhesion and enhances mechanical properties of the printed structures. This talk will focus on transitioning these concepts to FFF of high temperature polymers, such as poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI). Specific areas of investigation include formulating multimodal blends of polymer molecular weights to control polymer diffusion during printing, as well as control of the distribution of crystalline PEEK through processing and post-processing protocols. In particular these results will emphasize the importance of controlling the crystallization of the PEEK in these studies. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S05.00008: A new class of high-performance metal-fiber thermoplastic composites for additive manufacturing Debapriya Pinaki Mohanty, Brian Arnold, Srinivasan Chandrasekar, James Mann We demonstrate a new class of thermoplastic composites processed by additive manufacturing that utilize aluminum alloy fibers in a Polyethylene Terephthalate Glycol (PETG) matrix. Al6061-T6 microfibers, ~30μm cross section and 0.5 mm length, are merged with a PETG matrix by filament extrusion, and then 3D printed by fused deposition modeling (FDM). The metal fibers are produced by Modulation-Assisted Machining, wherein a low-frequency, sinusoidal oscillation is continuously superimposed onto a cutting process. The discrete fibers produced by the cutting have distinct characteristics, including uniform morphology (shape), roughened surface texture, and fine-grained microstructure, compared to conventional fiber processing. A range of particulate/fiber morphologies can be produced from virtually any metal or alloy, enabling the high-performance metal-fiber composites for additive manufacturing. The mechanical properties of the aluminum fiber/PETG composite show important advantages over other commercially available composites. Fiber-matrix combinations are discussed, along with performance benefits and applications. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S05.00009: Controlling structural and mechanical anisotropy in thermoplastic elastomers by 3D printing Alice S Fergerson, Emily C Davidson Traditional manufacturing techniques lack the ability to produce controlled hierarchical structures approaching the level of complexity that exists in biological systems. 3D printing of nanostructured materials brings us closer to this goal by providing macroscopic geometric control over a printed architecture coupled with nanoscale control over material structure along the print path. We focus on material extrusion 3D printing of thermoplastic elastomers to induce domain orientation resulting in anisotropic mechanical properties. We examine both how the complex processing flows of 3D printing and post-printing thermal annealing impact domain orientation. By designing print paths for these soft and mechanically anisotropic materials, we will enable fabrication of highly tailored architectures with desirable macroscopic mechanical behavior, such as shock absorption and local strain isolation. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S05.00010: Weld formation between polymer films subject to a thermal gradient -- insights from Molecular Dynamics simulations Mauro L Mugnai, Jonathan Seppala, Peter D Olmsted The weld between adjoining polymer filaments is formed by polymers diffusing across the interface. This process has important scientific and technological applications. In the simplest, symmetric case the two filaments are constituted of identical polymers in the same thermodynamic state. However, in some cases asymmetric settings are of interest. For instance, in polymer extrusion additive manufacturing, a high-temperature liquid polymer melt is placed in contact with a room-temperature glassy substrate, which results in material and heat exchange across their interface. Here, we investigate whether and how this asymmetric interdiffusion differs from the symmetric setup. We present results of Molecular Dynamics simulations of polymer films that are first equilibrated at a given temperature and then placed in contact with each other. As the films are laid side-by-side, polymers begin interdiffusing. By comparing symmetric, isothermal films, and asymmetric pairs equilibrated at different temperatures, we explore how the thermal gradient influences the formation of the weld. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S05.00011: Advanced manufacturing of multi-stable metamaterials Taylor E Greenwood, Md Nahid Hasan, Pai Wang, Yong Lin Kong We design and experimentally evaluate a new class of metamaterials capable of achieving multiple stable morphologies, which can be tailored to respond to external stimuli. Further, we engineer the metamaterial to achieve reconfigurations with a high fatigue resistance and expansion ratio. Ultimately, we anticipate that the multi-stability of an expandable structure can enable a broad range of biomedical devices. |
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