Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W33: Polymer Crystals and Crystallization IFocus
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Sponsoring Units: DPOLY DSOFT DMP Chair: Christopher Li, Drexel Univ Room: 505 |
Friday, March 6, 2020 8:00AM - 8:12AM |
W33.00001: Polymer epitaxy under heterogeneous confinement Jason Liu, Yang Xia, Geoffrey Zheng, Mikko Haataja, Craig Arnold, Rodney Priestley It is challenging to grow polymer crystals which are aligned over long length scales due to the inherent tendency of polymer lamellae to undergo spherulitic branching and splaying during growth. One approach to the creation of ordered and aligned polymer structures is by epitaxial crystallization. Typically, crystallization proceeds in a film of uniform thickness, in which polymer crystals nucleate and grow along rotationally symmetric, epitaxially matched crystallographic directions. In this work, we heterogeneously confine the film into spatially disparate regions of varying thickness to separate the nucleation and growth processes, allowing oriented arrays of epitaxial crystals to grow unimpeded over long distances. We uncover the hierarchical structure of polymers crystallized under heterogeneous confinement and elucidate the undercooling and molecular weight dependencies of pattern formation with experiments and phase-field simulations. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W33.00002: Understanding polymer crystallization undergoing zone annealing Alejandro Krauskopf, Andrew Jimenez, Sanat Kumar, Elizabeth Lewis, Bryan Vogt, Julia Pribyl, Brian C Benicewicz Zone annealing is a process through which a temperature gradient is translated at a set velocity across a polymer sample of interest, differentiating it from other crystallization processes by its inherent directionality. Through the application of the Hermans orientation function to our small-angle X-ray scattering detector patterns, we explore the extent of anisotropy that the process imparts on both the pure polymer and the polymer nanocomposite systems, with a focus on the lamellar orientation for the former and the nanoparticle arrangement for the latter. We also utilize differential scanning calorimetry to quantify the effects that the process has on the crystalline content and the melting temperature of the materials. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W33.00003: Tie Molecules and the Brittle-to-Ductile Transition in Near-Monodisperse and Bidisperse Linear Polyethylene Seong Hyuk Cho, Richard Register The Huang-Brown (HB) model predicts that tie molecules (TM), polymer chains that connect different crystalline lamellae across the amorphous layer, form when the end-to-end distance of the coil in the melt (R) exceeds the intercrystalline spacing (d) in the solid state, i.e., the TM probability should scale with R/d. To test the HB model, we synthesize narrowly-distributed (dispersity < 1.2) linear PEs of varying molecular weight (M) using ring-opening metathesis polymerization of cyclopentene followed by hydrogenation. Each PE is either quenched or slowly-cooled from the melt to vary the thermal history, giving two different d values. Uniaxial tensile tests of these PEs show a rather abrupt brittle-to-ductile transition (BDT) with increasing M, but the transition occurs at different R/d for the different crystallization conditions, in the contrast to the HB prediction. Quenched blends with variable contents of high-M PE in a low-M PE matrix show a BDT at the same HB tie chain probability as the quenched PEs. The differences among the values of R/d at the BDT for PEs with different thermal histories and hydrogenated polybutadiene (literature data) suggest that the degree of crystallinity has a significant influence on the value of R/d at the BDT. |
Friday, March 6, 2020 8:36AM - 9:12AM |
W33.00004: Flow Induced Crystallization: Insights from Molecular Simulation Invited Speaker: Gregory Rutledge Crystallization is an essential step in the processing of most polymers. It takes place under conditions of rapid cooling and high strain rate, and is strongly accelerated relative to quiescent conditions. The initial step in this process is flow-enhanced nucleation (FEN), which occurs on time and length scales that are hard to capture experimentally. To resolve this problem, we use nonequilibrium molecular dynamics simulations to characterize FEN from a melt of linear polyethylene-like chains. Both short and long (entangled) chains are simulated. First, methods are described for identifing the critical nucleation event using mean first-passage times (MPFT). Fitting of the data to a master equation is used to extract important thermodynamic and kinetic quantities. Results for nucleation kinetics accelerated under different modes of deformation, e.g. simple shear or uniaxial extension, and rates of strain are used to assess several of the existing models in the literature for flow-enhanced nucleation, based on their abilities to describe the data accurately, and new models based on the orientational ordering of Kuhn segments induced by flow are proposed. Evidence is presented for a breakdown of classical nucleation theory for entangled polymer melts at high strain rates, which in turn is traced to the flow-induced formation of nematic domains in the melt. The appearance of such domains suggests a different perspective on the underlying physics of flow-enhanced nucleation of long chain molecules. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W33.00005: Stereoregularity, Molecular Dynamics, and Unusual Crystallinity of Hydrogenated Polynorbornenes: Configurational Disorder Toshikazu Miyoshi, Navin Kafle, Yuta Makita Solid-state NMR spectroscopy can be used to study both the structure and dynamics of macromolecular systems that exhibit different degrees of order to understand the fundamental properties of materials. One such point of interest is to determine the difference of a polymer’s structure, local dynamics and phase transition between various isomers of semicrystalline polymers. Recently, a thorough study on stereospecific ring-opening metathesis polymerization has been conducted on norbornenes making the synthesis and the study of hydrogenated polynorbornene (hPNB) stereoisomers possible. The unique local dynamics, phase strucutre, and phase transition of atactic- syndiotactic- and isotactic-hPNBs will be shown and their relationships will be discussed. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W33.00006: Crystallization of Asymmetric PEO-b-PCL from Different Solvents Ryan Van Horn Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) copolymers have received a lot of attention due to their biocompatibility and amphiphilicity. One unique characteristic is that PEO and PCL have similar crystallization behavior, thus making them a robust model for phase behavior studies. Our previous work showed that the crystallization order could be switched in symmetric copolymers (nearly equal mass fraction) through selective solvent interactions. Further work has been done to identify similar behavior in asymmetric systems. Relative crystallinity and morphology are varied in as-cast films based on solvent characteristics. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W33.00007: Symmetry breaking via polymer chain overcrowding in molecular bottlebrush crystallization Christopher Li, Hao Qi, Mark Staub, Daniel Henn, Bin Zhao One of the fundamental laws in crystallization is translational symmetry, which accounts for the profound shapes observed in natural mineral crystals and snowflakes. Spherical polymer crystalsomes have been grown and investigated in the context of spherical crystallography, where translational symmetry is broken be confining crystal growth in a curved liquid/liquid interface. In this talk, we present the spontaneous formation of spherical hollow crystals with broken translational symmetry in crystalline molecular bottlebrush (mBB) polymers. The unique structure was named as mBB crystalsome (mBBC), highlighting its similarity to the classical molecular vesicles. Fluorescence resonance energy transfer (FRET) experiments showed that the mBBC formation was driven by local chain overcrowding-induced asymmetrical lamella bending. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W33.00008: Improving Crystallite Size and Orientation in Organic Semiconductor Thin Films using PDMS-Assisted Crystallization Vesta Zhelyaskova, Prachi Sharma, Daniel Dessau, Sean Shaheen We aim to develop a scalable, solution-based method for growing crystalline organic semiconductor thin films, which can be used in a variety of electronic charge transport, metal doping, and device integration studies. Using a polydimethylsiloxane (PDMS)-assisted deposition method for fullerenes, we grew polycrystalline C60 thin films on plain glass, between gold electrodes on glass, and on silicon substrates under a range of growth conditions. AFM characterization revealed that the films (1) were typically 200-300 nm thick, (2) were made up of crystallites extending up to 200 μm, and (3) had crystalline microstructures that vary with choice of solvent, temperature, and substrate pre-treatment. Films grown from carbon disulfide solutions covered larger areas than those grown out of o-dichlorobenzene—an interplay between the C60’s low solubility and the PDMS’s absorption of nonpolar solvents. Growth at lower temperatures resulted in uniformly aligned crystallites, which formed farther from the PDMS-substrate boundary. Growth along and between gold contacts resulted in nucleation of similarly aligned crystallites at the gold's edge. Here we discuss the growth kinetics of these films along with their electronic, structural, and spectroscopic characterizations. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W33.00009: Wang-Landau Simulation of the Free Energy Surface of Crystallization in a Polymer Melt Pierre Kawak, Andrew Scott Gibson, Logan Stewart Brown, Beverly Delgado, Douglas Tree Semicrystalline polymers comprise as much as 70% of the hundreds of million of tons of polymers produced worldwide. However, the polymer crystallization process remains imperfectly understood. Recently, there has been a lively debate in the literature concerning the applicability of classical nucleation theory to the primary nucleation process in a polymer melt. Recent experimental observations have lead several authors to propose mesomorphic phases that mediate the melt-crystal transition. To investigate these claims, we have constructed a GPU-accelerated Wang-Landau Monte Carlo algorithm that employs both configurational bias and bond breaking moves. Our algorithm has the ability to directly sample the density of states, which can be used to construct a free energy surface as a function of relevant order parameters for crystallization. Our initial results show that we are able to capture both melt and crystalline phases with speed increases of about two orders of magnitude greater than with a comparable serial algorithm. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W33.00010: Crystallization and self-nucleation of conjugated polymers Lucia Fernandez-Ballester, Ramin Hosseinabad, Jesse Kuebler It is well known that the specific conditions under which polymer crystallization occurs dictate the resulting semicrystalline morphology and, therefore, the final mechanical, optical, and diffusive properties of the solidified material. For conjugated polymers, even seemingly small differences in crystallinity, orientation, or tie chains can result in significant changes in charge transport properties; however, the interplay between chain structure, crystallization conditions, and structure development remains elusive because they are typically processed in solution (for example, by spin-coating) where ill-defined conditions are prevalent. Here, we explore the role of molecular attributes on the crystallization behavior of poly-3-hexylthiophene under well-defined conditions. The results indicate that molecular characteristics play an important role in the way crystallization proceeds, and that self-nucleation strategies can be used effectively to manipulate crystallization conditions. |
Friday, March 6, 2020 10:24AM - 10:36AM |
W33.00011: Paradigm on the Growth Kinetics of Lamellar Polymer Crystals Wenbing Hu Growth kinetics of lamellar polymer crystals is the holy grail topic in the crystallization mechanism of polymers.There exist so far many controversial arguments, but only three of them have derived the kinetic equations of the linear crystal growth rate at the lateral front of lamellar crystals: Lauritzen-Hoffman model, Sadler-Gilmer Model and the intramolecular crystal nucleation model. Three equations hold however similar forms. This fact reveals the long-existing paradiam during the development of these three models.The latest intramolecular nucleation model provides interpretations to those unique kinetic phenomena of polymer crystallization, such as the origin of chain-folding, the determination of fold-length, molecular-length segregation, sequence-length segregation, three-regime transitions, linear concentration dependence, and self-poisoning growth with integer-folding of short chains. |
Friday, March 6, 2020 10:36AM - 10:48AM |
W33.00012: Tuning Nanoparticle Dispersion to Control Confined Polymer Crystallization for Induced Ordering Andrew Jimenez, Abdullah Al Torbaq, Alejandro J Müller, Sanat Kumar Extremely slow isothermal processing presents the ability to control nanoparticle dispersion in semicrystalline polymers, hierarchically ordering them in the amorphous regions of the crystal structure and providing mechanical reinforcement to the composite. The necessity for “extremely slow processing” is, of course, not ideal despite its favorable outcome. Recent work began to understand the tradeoff of crystallization rate and the subsequent particle alignment, both of which depend strongly on nanoparticle grafting and concentration. Building from these insights, we have worked to tune nanoparticle parameters (size and grafting) to manipulate their influence on nucleation and crystal growth rate by effectively controlling polymer confinement and polymer-particle interactions. Designing relative differences in nanoparticle dispersion and mobility allows for increased control over the crystallization rate of the polymer matrix and the subsequent nanoparticle structure of the composite. |
Friday, March 6, 2020 10:48AM - 11:00AM |
W33.00013: Kinetics of Shape-fixing in Semicrystalline Shape-memory Networks Jeh-Chang Yang, Mitchell Anthamatten Crystallization of elastic polymer networks can enable shape-fixing of elastically deformed shapes which can subsequently be melted to regenerate stress or revert to the original shape. The initial step of a shape-memory cycle is shape-programming and involves the formation of connected crystal domains that can prevent the release of stored elastic strain energy. Crystallization kinetics play a critical role in determining the conditions required for sufficient shape-fixing. Here, we assess how imposed strain and undercooling affect crystallization kinetics and concomitant stress loss of crosslinked poly(caprolactone)s. Isothermal crystallization experiments were performed that involve in situ x-ray scattering combined with stress decay measurements. The main finding is that that only a small amount of crystallization is needed to significantly reduce tensile stress. This result is valid for low levels of strain and undercooling, and it has broad implications for engineering new shape memory materials. |
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