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 Y12: Recent Progress in Polymer CrystallizationInvited
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Sponsoring Units: DPOLY Chair: Lucia Fernandez-Ballester, University of Nebraska - Lincoln Room: Room 235 |
Friday, March 10, 2023 8:00AM - 8:36AM |
Y12.00001: Tuning crystallization pathway via confinement Invited Speaker: Christopher Y Li Polymer crystallization is often sensitive to the environment and chain defects. In this talk, we present how to tune polymer crystallization pathways by introducing soft confinement and varying the chain structure. The first part of the talk will be focusing on templating crystallization using a liquid/liquid interface. Both flat and curved interfaces will be discussed. In the second part of the talk, we will show that by introducing non-crystallizable moieties into the chain, the morphology and structure of polymer crystals can be significantly modified. These non-crystallizable moieties can also be viewed as internal confinement for chain crystallization. The discussion will be particularly focused on shape-symmetry incommensurate crystals with broken translational symmetry. We emphasize that not only can tuning crystallization pathways shed light on understanding crystallization mechanisms, but it also provides a promising way to fabricate functional materials. |
Friday, March 10, 2023 8:36AM - 9:12AM |
Y12.00002: Crystallization of Sustainable Polyethylene-Like Materials Invited Speaker: Rufina G Alamo Bio-sourced polyethylene-like polymers have been synthesized as possible substitutes for commodity polymers derived from fossil fuel feedstocks. Their crystalline and mechanical properties are of interest in the path to developing a more sustainable, circular plastics economy. We are interested in understanding their solidification behavior from the melt and the semicrystalline morphology acquired under different crystallization modes. Recent studies of polymorphism, melting behavior and crystallization kinetics of polyethylenes with moieties placed at an exact equal distance along the backbone will be presented with especial focus on the crystalline properties of precision polyethylenes with acetals and esters, under rapid and isothermal crystallization from the melt.(1-6) All display unusual discrete crystallization rate minima with increasing crystallization temperature. Such inversions in the temperature coefficient of the crystallization kinetics correlate with transitions between crystalline structures differing in packing symmetry (polymorphs), or in a step-increase in crystal thickness. At the rate minima, the level of crystallinity is very low. Hence, the rate minima are “kinetic traps” of relevance in processing these materials from the melt. The origin of the rate minima will be discussed. |
Friday, March 10, 2023 9:12AM - 9:48AM |
Y12.00003: Recent Progress in Molecular Simulation of Flow Induced Crystallization: Biaxial Flows Invited Speaker: Gregory C Rutledge Crystallization is a defining step in the fabrication of most polymeric materials. It occurs predominantly through the mechanisms of nucleation and growth from an amorphous melt or solution, which determine the ultimate morphology and properties of the resulting product. In industrial processes like fiber spinning, film blowing, extrusion, injection molding, and fused deposition modeling, crystallization takes place while the polymer is in a state of flow, which can significantly alter the crystallization kinetics, or even change the nature of nucleation and growth qualitatively. Nucleation, in particular, is very sensitive to flow-induced structures in the melt. However, nucleation occurs on time and length scales that are hard to observe experimentally. We use molecular simulations to characterize nucleation in flowing melts of linear, polyethylene-like chains, both with and without entanglements. Using nonequilibrium molecular dynamics and an analysis of mean first-passage times (MFPT), we have previously reported the dependence of enhanced nucleation rates of the structure and thermodynamics of the flowing melt in simple shear and uniaxial extensional flow. More recently, we have extended this work to include the more general cases of equibiaxial and nonequibiaxial flows. We find that a relationship describing flow enhanced nucleation as a function of orientational ordering of Kuhn segments models the kinetics most robustly for a diverse set of flow states. Furthermore, we reveal the onset of nematic ordering, previously observed for uniaxial extensional flows, in entangled polymer melts undergoing nonequibiaxial flow above a critical state of strain rate and flow asymmetry. Such nematic ordering is found to support nucleation preferentially, and is likely responsible for at least a part of the enhancement in nucleation observed in entangled polymer melts. |
Friday, March 10, 2023 9:48AM - 10:24AM |
Y12.00004: Revisiting Crystallization Pathways in PEO-b-PCL Copolymers Invited Speaker: Ryan M Van Horn Hierarchical assembly in block copolymers (BCPs) is a critical process and structural component for tailoring macroscopic properties in these diverse materials. Crystallization in BCPs has been studied under a variety of conditions. Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) copolymers have received a lot of attention due to their biocompatibility and amphiphilicity. Interestingly, PEO and PCL are miscible and have similar transition temperatures. These features allow for a diverse and robust set of parameters, such as chain weight fraction, thermal history, casting solvent, aging or annealing conditions, etc., to be used for tailoring their physical structure. We have shown that crystallization order and crystallinity can be manipulated using different film preparation conditions. Hydrophobic PCL contains ester bonds capable of hydrolytic cleavage, and hydrophilic PEO promotes water uptake in these amphiphilic materials. Both processes, water uptake and degradation, are dependent on the crystallinity of the two blocks. By preparing films using various solvent casting and thermal preparation techniques, we can begin to correlate structure-property relationships to the hierarchical assembly of crystalline-crystalline copolymers. |
Friday, March 10, 2023 10:24AM - 11:00AM |
Y12.00005: Polymer Chains Fold Prior to Crystallization Invited Speaker: Toshikazu Miyoshi Crystallization of long polymer chains changes their own structures from a random coil state to a partially folded structure in the thin crystal lamellae. There have been continuous debates in the folding mechanism and structure of long polymer chains in the melt and solution-grown crystals. In this talk, I would like to summarize our recent efforts on understanding folding structure of a semicrystalline polymer in the melt-grown crystals by using solid-state NMR spectroscopy. NMR spectroscopy does not require three-dimensional long-range order and thus is capable of being applied to structural study even in a glassy state. First, we focus on the folding structure or local chain trajectory of poly(L-lactic acid) (PLLA) in a glassy state. Comparisons of the folding structure between the crystalline and glassy states will provide a new mechanism of the folding event and polymer crystallization. Second, we prepared various 13C enriched PLLAs with different molecular weights (Mw = 2.5k – 300k g/mol) across critical entanglement length (Mc = 16k g/mol). We observed molecular weight dependence of chain folding structure of PLLA. Based on the experimental results, I would like to discuss a possible mechanism for chain folding in the melt-grown crystal. |
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