Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K36: Recent Progress in Polymer CrystallizationInvited
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Sponsoring Units: DPOLY Chair: Toshikazu Miyoshi, The University of Akron Room: BCEC 205C |
Wednesday, March 6, 2019 8:00AM - 8:36AM |
K36.00001: Reaching the structural intimacy of polymer crystals and spherulites. Invited Speaker: Bernard Lotz The complex architecture of polymer crystals involves four interconnected levels of organization: chain conformation, unit-cell, lamellar crystals and spherulites. Many of the fundamental features of and connections between structural levels were established with the investigation of solution grown single crystals of structurally “simple” polymers such as polyethylene. Polymers with more complex chemical structure or conformation (e.g. helical) add further constraints or requirements on the crystal structure and/or the folds conformation/organization. These constraints lead to unusual features of their diffraction pattern (e.g. specific streaks) or morphology (e.g. lamellar branching, scrolled crystals). Their analysis helps reach some very finer details of the crystalline polymers’ buildup. Older and very recent examples include the impact and identification of helical hand in crystal structures and the origin of unbalanced surface stresses in the lamellae fold surfaces. These stresses induce twisted and scrolled lamellae. Observation of scrolled single crystals of even-even nylons helped solve the decades long issue of their negative spherulites’ architecture. |
Wednesday, March 6, 2019 8:36AM - 9:12AM |
K36.00002: Shape-Symmetry Incommensurate Polymer Crystals Invited Speaker: Christopher Li Crystallization is ubiquitous in nature and semicrystalline polymers are of crucial importance in our daily life. Because of their long chain nature, polymers crystallize via a more complex pathway, leading to profound metastable states and morphology. This talk will focus on polymer crystals whose shape is incommensurate with three-dimensional translational symmetry. Examples are helix, tubes and spheres. Not only can this shape-symmetry incommensurateness arise from the intrinsic characteristics of the crystal such as unbalanced chain folding and/or local stress, it also can be imparted by nanoscale confinement. Bothe cases will be discussed, and emphasis will be given to the formation mechanism, associated properties and possible applications of these unique polymer single crystals. |
Wednesday, March 6, 2019 9:12AM - 9:48AM |
K36.00003: The Role of Entanglements for Polymer Crystallization Invited Speaker: Jens-Uwe Sommer We use a coarse-grained polymer model to study the crystallization and melting behavior of long polymer chains in the dense state under various conditions. Our primary goal was to investigate the impact of the local state of entanglement on the properties of the lamellar crystal, in particular on the thickness selection, using algorithms to calculate the primitive path of the chains. In situ analysis of the local entanglement length prior to crystallization and analysis of the stem length and crystallinity at the same location reveals a direct correlation between the entanglement length and crystallization properties in the nucleation-controlled regime [1]. We have investigated various scenarios to change the apparent entanglement length in the system such as rapid cooling and cold-crystallization protocols, dilution of the melt by short chains, and the influence of solid substrates [2-4]. All studies confirm the correlation between entanglement length and thickness selection in the dense state. First results on non-concatenated ring polymer melts display an increase of the lamellar thickness and in the degree of crystallization as compared to otherwise identical linear counterparts subject to the same thermal history [5]. Our studies suggest a topological viewpoint on thickness selection in polymer crystals. |
Wednesday, March 6, 2019 9:48AM - 10:24AM |
K36.00004: In Situ Real-Time Observation of Polymer Folded-Chain Crystallization by Atomic Force Microscopy at the Molecular Level Invited Speaker: Jiro Kumaki The crystallization process of a folded-chain crystal (FCC) was clearly visualized at the molecular level in situ and in real time for the first time [1]. We deposited an amorphous isotactic poly(methyl methacrylate) monolayer on mica, and the crystallization of the monolayer under high humidity was followed by atomic force microscopy. Detailed crystallization behaviors, especially, the stepwise growth of the FCC with blocks shorter than the chain, chain slipping in the FCC, the formation of an anisotropic nucleus and its growth, and the formation of a small nucleus with a short lifetime, were clearly visualized at the molecular level. The stepwise growth of the FCC differed from that expected by the classical Lauritzen-Hoffman theory and was consistent with recent reports that indicated the formation of some ordered states in the amorphous phase. In addition, the crystallization process of a poly(lactide), which formed an extended-chain crystal (ECC) in a monolayer was also visualized, and will be discussed. |
Wednesday, March 6, 2019 10:24AM - 11:00AM |
K36.00005: Crystallization of Precision Polyethylenes Invited Speaker: Rufina Alamo The self-assembly, 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 recent studies of the crystalline properties of precision polyethylenes with halogens (as pendant), and acetals (in-chain) groups under rapid and isothermal crystallization from the melt.1-5 The observed discrete minima in the temperature coefficient of the crystallization kinetics correlates with transitions between polymorphic structures that differ in packing symmetry. The minima or retardation of crystallization kinetics may be due to self-poisoning at the growth front or to differences in nucleation and growth between two polymorphs at the transition temperature. Control over different layered crystalline structures, demonstrate the ability of these novel systems to generate new polyethylene-based materials based on nanostructures at the lamellar and sub-lamellar level not feasible in classical branched polyethylenes. |
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