Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X33: Polymer Crystals and Crystallization IIFocus
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Sponsoring Units: DPOLY DSOFT DMP Chair: Toshikazu Miyoshi, Univ of Akron Room: 505 |
Friday, March 6, 2020 11:15AM - 11:27AM |
X33.00001: Controlling the Mechanical Behavior of Hydrogenated Polynorbornene Jared Klein, Richard Register Hydrogenated polynorbornene (hPN) synthesized via ring-opening metathesis polymerization is a semi-crystalline polymer even while atactic, as it is able to accommodate stereodefects within the crystal. We have previously shown control over phase behavior in hPN via epimerization of the cyclopentylene ring in the backbone structure. The polymorphic transition temperature into a rotationally-disordered state, Tcc, is strongly affected by epimerization, while epimerization has only a minor effect on the melting temperature, Tm, and no appreciable effect on the total crystallinity (J. P. Klein and R. A. Register, J. Polym. Sci. B, 57, 1188 (2019)). In this talk, the effect of epimerization on both the stress-strain behavior and dynamic mechanical thermal properties are discussed. Epimerization causes a decrease in both the Young’s modulus and the yield strength of the polymer, and it also reduces the breadth of the modulus-vs.-T plateau region (above Tg) significantly, in line with the decrease in Tcc. hPN-based polymers with a pyrene endgroup show a strong fluorescence sensitivity to melting/crystallization, and work is underway to evaluate their utility in probing other hPN transitions. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X33.00002: What happens upon annealing of pre-drawn semicrystalline polymers? Travis Smith, Shiqing Wang As part of efforts to understand mechanical behavior semicrystalline polymers under large deformation, we investigate what happens to predrawn semicrystalline polymers upon annealing at elevated temperatures. For instance, LLDPE drawn at room temperature will neck to its characteristic draw ratio around 5.5 and will shrink by 10% when unloaded but will remain in this highly stretched state for many years. Such predrawn PE samples will either exhibit various levels of retractive stress when held at a fixed length or shrink by different amounts, depending on the annealing temperature. The physical meaning of this characteristic will be explored experimentally, first mechanically and eventually by in situ WAXS and SAXS measurements. Specifically we will search for evidence to support our concept that there is partial melting upon annealing due to the chain tension produced by the pre-cold-drawing, at temperatures well below the melting temperature. The universality of the phenomenology and its molecular interpretation is explored by making a similar investigation of a second semicrystalline polymer, poly(ethylene terephthalate), drawn above its glass transition temperature T = 70 Celsius. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X33.00003: Entanglement Effect on Chain-Folding Structure in Semicrystalline Polymer Blends Fan Jin, Toshikazu Miyoshi Entanglement effect on chain-folding structure of semicrystalline polymers is not clearly understood over the past decades. Very recently, we demonstrated that Poly(Lactic Acids) chains with three different molecular weights of 46K, 90K, and 320K g/mol do not change adjacent re-entry structure under different supercoolings. It was suggested that entanglement of polymer chains limit adjacent re-entry number in the melt-grown crystals. In this study, we isothermally crystallize polymer blend samples consisting of long and short Poly(Lactic acid) chains from the melt state. Only long polymer chains are labeled by 13C. 13C-13C double quantum (DQ) spectroscopy is applying to study local chain-folding structure of PLLA as a function of blending ratio and as a function of molecular weight of short PLLA chains. |
Friday, March 6, 2020 11:51AM - 12:27PM |
X33.00004: Flow-Induced Crystallization of Polymers during Multi-Axial Deformation Invited Speaker: Liangbin Li Flow- or stretch-induced crystallization (FIC/SIC) is believed to be mainly responsible for the excellent mechanical properties of polymers during real processing. The development of synchrotron radiation (SR) X-ray scattering techniques with high time resolution has been a mainstream research tool to study the structural evolution of polymers under complex external fields. The FIC behaviors of polymers during multi-axial deformation like biaxial stretching, film blowing and service of sounding balloon has been systematically studied with the combination of in-situ SR X-ray scattering and the custom-built devices. Considering the phenomenon of frustrating SIC for natural rubber during biaxial stretching, we proposed a new model for SIC based on the results of theoretical calculation and the in-situ X-ray scattering, which decoupled the free energy contributions of chain orientation from that of conformational entropy reduction. This model is also suitable for the crystallization of polymers under other flow fields. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X33.00005: Homogeneous crystal nucleation – Nucleation kinetics and thermal stability of nuclei Christoph Schick, Ruslan Adrianov, Timur Mukhametzyanov, Rene Androsch Crystal nucleation in polymer melts at common laboratory cooling rates (< 10 K/s) is typically heterogeneous. Studying homogeneous crystal nucleation in bulk samples requires bypassing the low-supercooling temperature range of pre-dominant heterogeneous nucleation. This became possible with the availability of fast scanning chip calorimetry. |
Friday, March 6, 2020 12:39PM - 12:51PM |
X33.00006: Are Spherulites Spherical? 3D Visualization of Semicrystalline Polymer Morphology Using Optical Tomography Shu-Gui Yang, Zhen-Zhen Wei, Goran Ungar, Pantea Kazemi, Hui-Jie Xie, Liliana Cseh, Hina Saba Spherulites, shish-kebab, cylindrites and other morphological features of bulk semicrystalline polymers have been studied for decades using methods such as polarized optical microscopy, TEM or AFM. For these studies either thin films or thin sections were used, giving 2D but not 3D pictures. The organization in the 3rd dimension has been implied rather than directly observed. Attempts at 3D imaging have been made with varying success using approaches, notably electron tomography (TEMT) and some other methods. Most studies focussed on polymer blends and block copolymers, relying on contrast produced by the chemically different components, although some remarkable images of crystal lamellae were obtained by TEMT. However 3D images of microstructure on the crucial 10-1000 micron scale, especially of single-component polymers or their nanocomposites, are still missing. Here we present first such images obtained by confocal microscopy using appropriate sample preparation and image processing. Already rather unsuspected features of 3D morphology are emerging, previously being hidden by the limitations of the conventional techniques. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X33.00007: Advanced Polymeric Particles Templated by Polymer Crystallization at Curved Liquid/Liquid Interface Mark Staub, Christopher Li Polymeric micro/nanoparticles have attracted significant interest in the past few decades due to their relevance in a number of fields. The methods commonly employed tend to provide particles that have simple morphology of spheres or cylinders that are inherently fluidic and dynamic due to the long chain nature of macromolecules. As more complex particles, in function and structure, are emerging as solutions to a variety of problems, simple and versatile methods to obtain them are a necessity. Towards this aim, our group has developed a miniemulsion crystallization process where polymer single crystal-like growth is confined to a dynamic liquid/liquid interface. This process produces unique hollow polymer capsules termed “crystalsomes” that have excellent mechanical properties compared to their amorphous counterpart the polymersome. This talk will focus upon using blends of amphiphilic block co-polymers in the miniemulsion process to template hierarchically structured crystalsomes. The block co-polymers serve as macromolecular surfactant along with the hydrophobic segment acting as the crystalline motif. It will be shown by altering the hydrophobic monomeric unit, its degree of polymerization, and the particle size a variety of crystalsomes with tunable porosity can be obtained. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X33.00008: Phenomenological Theory of Prefreezing at the Solid-Melt Interface Oleksandr Dolynchuk, Muhammad Tariq, Thomas Thurn-Albrecht Crystallization of liquids is usually initiated at the interface to a solid. The underlying process can be either heterogeneous nucleation or the recently observed process of prefreezing. The latter is the reversible and abrupt formation of a crystalline layer at the interface melt-solid at temperatures higher than the bulk melting point. We present a phenomenological theory of prefreezing and derive such equilibrium properties as the temperature dependent thickness of the prefrozen layer, the prefreezing temperature Tmax, and the mesoscopic jump of thickness at Tmax.1 The theory provides a clear thermodynamic explanation of the abrupt formation of a crystalline layer as a result of the interplay of the interfacial energies γsub,cry, γcry,melt, and γsub,melt. The prefreezing temperature Tmax was found to depend on all three interfacial energies and bulk parameters. However, we show that the difference of the interfacial energies Δγ = γsub,melt – (γsub,cry + γcry,melt) acts as a driving force for prefreezing, as Tmax tends to increase with increasing Δγ. The analytical outcomes are in accordance with recent experimental results for polyethylene and poly(ε-caprolactone) crystallized on graphite and MoS2 via prefreezing. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X33.00009: Role of flow-induced nematic order in polyethylene nucleation Wenlin Zhang, Ronald Larson We employ united-atom molecular dynamics (MD) simulations to quantify the role of nematic order in polyethylene (PE) nucleation. In our simulations, stretched periodic PE chains are blended with free PE chains of the length of 500 and 1000 backbone carbons (C500 and C1000). These bidisperse systems are the simplest realizations of real polymer samples, in which only polymers with long branches or high molecular weights are stretched by flows. By simulating isothermal nucleation and performing mean-first-passage time analysis for the growth of the largest nucleus in our simulations, we show that the nucleation rate of PE increases exponentially with increasing average nematic order of monomers. We also validate the predicted quiescent nucleation rates by computing the crystallization half-time at various temperatures using the crystal growth velocity, sampled from simulations of isothermal crystallization of chains near crystalline slabs, and the Avrami equation. The predicted crystallization half-times agree with experiments, suggesting our predicted nucleation rates are reasonable. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X33.00010: Crystallization and liquid crystallinity in heptadecanylcarbazole-dithienylbenzothiadiazole (PCDTBT) conjugated polymers Ryan Fair, Enrique Gomez Conjugated polymers exhibit rich phase behavior including liquid crystalline and crystalline phases. Conflicting reports of one such polymer, poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), have claimed the material to be amorphous or semicrystalline. We use oscillatory shear rheology to demonstrate that PCDTBT exhibits liquid crystallinity by identifying the nematic to isotropic temperature. We also find a crystalline phase when annealed at high temperatures, which is likely due to the high Tg, near 120 oC, that is identified also through rheology. We corroborate the phase behavior using X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy. High resolution transmission electron microscopy reveals the consequences of annealing in the amorphous or liquid crystalline phase prior to crystallization, and yields images of the crystalline morphology that are produced under these different conditions. |
Friday, March 6, 2020 1:39PM - 1:51PM |
X33.00011: Analyzing morphological and optical properties of poly(3-hexylthiophene) (P3HT) via emitted light’s polarization Huan Nguyen, Paulo T Araujo With the improvement in synthetic methodologies, polythiophenes and specifically poly(3-hexylthiophene) (P3HT) have become forerunners in the field of conjugated polymers. We study P3HT’s morphological and optical properties via measurements of absorption and polarization-resolved photoluminescence via Stokes spectroscopy. Our recent results show that P3HT’s aggregation behaviors change drastically when using chloroform stabilized and non-stabilized by amylene. Specifically, P3HT drop-cast films made from stabilized chloroform presented H-aggregates, while similar samples using non-stabilized chloroform exhibited J-aggregates. Here, we hypothesize that the amylene from stabilized chloroform induces a higher probability for the stacked coupling of isolated chains via weak van-der-Waals force leading to the formation of H-aggregates. To rule the influence of amylene out, we are currently performing a set of analyses and experiments consisting of temperature-dependent measurements, thermal annealing, various P3HT chain sizes, and blended MeOH@Chloroform solvents. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X33.00012: Computational Model for End-On LCEs James Waters, Anna Balazs
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Friday, March 6, 2020 2:03PM - 2:15PM |
X33.00013: WITHDRAWN ABSTRACT
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