Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B32: Focus Session: Polymer Crystallization and Morphology |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Xinfei Yu, NIST Room: 340 |
Monday, March 18, 2013 11:15AM - 11:51AM |
B32.00001: Disentangled solid state and metastable polymer melt; a solvent free route to high-modulus high-strength tapes and films of UHMWPE Invited Speaker: Sanjay Rastogi Ultra High Molecular Weight Polyethylene (UHMWPE) having average molar mass greater than a million g/mol is an engineering polymer. Due to its light-weight, high abrasion resistance and biocompatibility it is used for demanding applications such as body armour, prostheses etc. At present, because of its high melt viscosity to achieve the uniaxial/biaxial properties in the form of fibers/films the polymer is processed via solution route where nearly 95wt{\%} of the solvent is used to process 5wt{\%} of the polymer. In past several attempts have been made to process the polymer without using any solvent. However, compared to the solvent processing route the achieved mechanical properties were rather poor. Here we show that by controlled synthesis it is feasible to obtain UHMWPE that could be processed free of solvent to make uniaxial tapes and biaxial films, having unprecedented mechanical properties, exceeding that of the solution spun fibers. We address some of the fundamental aspects of chemistry, physics, rheology and processing for the development of desired morphological features to achieve the ultimate mechanical properties in tapes and films. The paper will also address the metastable melt state obtained on melting of the disentangled crystals and its implication on rheology in linear and nonlinear viscoelastic region. Solid state NMR studies will be applied to establish disentangled state in solid state to the polymerisation conditions. References: Macromolecules 2011, 44(14), 5558-5568; Nature Materials 2005, 4, 635-641; Phys Rev Lett 2006, 96(21), 218303-218205. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:03PM |
B32.00002: A simple model for heterogeneous nucleation of isotactic polypropylene Michael Howard, Scott Milner Flow-induced crystallization (FIC) is of interest because of its relevance to processes such as injection molding. It has been suggested that flow increases the homogeneous nucleation rate by reducing the melt state entropy. However, commercial polypropylene (iPP) exhibits quiescent nucleation rates that are much too high to be consistent with homogeneous nucleation in carefully purified samples. This suggests that heterogeneous nucleation is dominant for typical samples used in FIC experiments. We describe a simple model for heterogeneous nucleation of iPP, in terms of a cylindrical nucleus on a flat surface with the critical size and barrier set by the contact angle. Analysis of quiescent crystallization data with this model gives reasonable values for the contact angle. We have also employed atomistic simulations of iPP crystals to determine surface energies with vacuum and with Hamaker-matched substrates, and find values consistent with the contact angles inferred from heterogeneous nucleation experiments. In future work, these results combined with calculations from melt rheology of entropy reduction due to flow can be used to estimate the heterogeneous nucleation barrier reduction due to flow, and hence the increase in nucleation rate due to FIC for commecial iPP. [Preview Abstract] |
Monday, March 18, 2013 12:03PM - 12:15PM |
B32.00003: Monte Carlo Simulations of Strain-induced Polymer Crystal Nucleation Wenbing Hu, Yijing Nie, Huanhuan Gao We performed dynamic Monte Carlo simulations of lattice polymer chains, to investigate primary crystal nucleation induced by a homogeneous stretching at high temperatures. We developed a new scheme to realize a homogeneous stretching of bulk polymer chains with their one chain ends fixed on a shifting plane and the other ends on a fixed plane. We observed a sudden decay of chain-folding probability in those newly emerged small crystallites, which indicated a transition of crystal nucleation from intramolecular mode to intermolecular mode. There exists a competition between two nucleation modes, as revealed by a theoretical fitting of the critical strains for mode transitions at various temperatures. The theoretical estimation is based on the classical nucleation theory. [Preview Abstract] |
Monday, March 18, 2013 12:15PM - 12:27PM |
B32.00004: Solid to solid beta to alpha form transition in crystalline structures of syndiotactic polystyrene (sPS) Tetsu Ouchi, Suguru Nagasaka, Atsushi Hotta The new solid to solid crystalline transition from beta to alpha forms in syndiotactic polystyrene (sPS) was discovered and analyzed. sPS has five crystalline structures: alpha, beta, gamma, delta, and epsilon forms. Among these crystalline structures, alpha and beta forms are two major crystalline structures due to their high mechanical properties. In this research, it was found that the transition was induced by mechanical strain well below the melting temperature of sPS (273 deg C) unlike the reverse transition from alpha to beta form observed at 260 deg C. The transition became more pronounced as testing temperature increased from 130 to 220 deg C. The transition should occur under the interaction of annealing process and mechanical strain, as the transition would not occur just by raising temperature. It was concluded from our experimental results that the destruction of the $\beta $ form first took place under mechanical strain, causing beta form to transform into not only alpha form but also mesomorphic alpha form. The hot environment had a great impact on the perfection and the promptness of the transition: testing temperature could accelerate the transition ending up with more perfect alpha form transformed from beta form through mesomorphic alpha form. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B32.00005: Molecular Structure of Semicrystalline Polyethylene Blends Studied by Broadband Coherent Anti-Stokes Raman Scattering Microscopy Young Jong Lee, Chad Snyder, Aaron Forster, Marcus Cicerone, Wen-li Wu Blends of polyolefins have been widely used to diversify and improve material properties and to avoid complications that exist in blending immiscible heterogeneous polymers. The properties of a blend quite often deviate from predicted ones with the linear combination of its constituent homopolymers or copolymers, likely due to microscopic phase separation and differing degrees of crystallization. However, the current measurement techniques for studying the structure of polyolefin blends are primarily based on bulk averaging methods such as calorimetry or neutron scattering or through solvent extraction of a lower melting component. As a result, development of new blends depends on mostly empirical approached, not based on microscopic structural information. We demonstrate here that a noninvasive imaging technique, based on coherent anti-Stokes Raman Scattering (CARS) microscopy, can provide microscopic structural information of a bimodal polyethylene blend. We discuss new findings of the spatial distribution of species with different molecular architectures and the orientation of their semicrystalline structures. [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B32.00006: Enhanced segmental mobility of Poly(lactic acid) in presence of water Omkar Vyavahare, Shaw Hsu The objective of this work was to understand the effect of water on the segmental mobility of Poly(lactic acid) (PLA). When PLA was crystallized by soaking it in water, the crystallization temperature was lowered significantly, allowing PLA to crystallize even below the generally accepted glass transition temperature (T$_{\mathrm{g}})$. PLA crystallized below 90$^{\mathrm{o}}$C has a metastable $\alpha $' crystalline phase. However, in presence of water, it formed a mixture of $\alpha $', and stable $\alpha $ crystalline phases. Water also had a prominent effect on the physical aging of PLA, with the polymer rapidly undergoing densification in the glassy state compared to the dry conditions. Dielectric relaxation studies of PLA with 0{\%} and 13{\%} d-lactide content revealed contradictory influence of water on their respective sub-T$_{\mathrm{g}}$ ($\beta )$ transitions. The $\beta $ transition was suppressed for PLA with no d-lactide content, while it got enhanced for PLA with 13{\%} d-lactide. These experiments demonstrate that water promotes interchain interactions and enhances segmental mobility. This allows the chains to have a conformation which provides an easier pathway with lower energy barrier for the transformation among various polymorphic states. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B32.00007: Molecular engineering of high-performance elastomeric materials Shengwei Deng, Michael Falk Polyurethane is a typical elastomeric material and among the most versatile materials today. It is a linear block copolymer consisting of alternating soft and hard segments with phase separation due to thermodynamic segmental incompatibility. Inspired by the hierarchical structure of spider silk, this kind of block copolymer can be synthesized with two distinct blocks that can differ in their propensity to crystallize. Either the soft or hard segments can be amorphous or semicrystalline. Recent experiments indicate that crystallizable segments lead to higher tensile strength and that systems with crystalline hard segment exhibit better stiffness, strength and mechanical toughness. Here we implement molecular dynamics simulation to investigate the influence of block architectures on mechanical properties and molecular chain movement. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B32.00008: Tuning Properties of Semi-Crystalline Polymers at Constant Crystallinity: Adjusting Rigid Amorphous Fraction and Crystallization Conditions by Solid-State Shear Pulverization Philip Brunner, John Torkelson Semi-crystalline polymers consist of both crystalline and amorphous regions, the latter of which can be subdivided into rigid amorphous fraction (RAF) and mobile amorphous fraction. The RAF does not undergo a glass transition at the measured Tg but may remain rigid up to the melting temperature of the crystalline regions. This means that RAF can quantified by DSC measurements related to the change in heat capacity in going from the glassy to liquid state upon heating. We have discovered that RAF levels in some semi-crystalline polymers can be altered dramatically by solid-state shear pulverization although the crystallinity level remains constant. We take advantage of this to demonstrate how permeation characteristics and mechanical properties of semi-crystalline polymers may be significantly altered by SSSP while maintaining constant crystallinity levels. Examples include nylon 11 in which oxygen permeability can be decreased by 50{\%} due to an increase in RAF, with the permeability reduction caused by nearly equal effects of RAF on solubility and diffusivity. Additionally, major changes in tensile properties of nylon 11 and polycaprolactone can be correlated with changes in RAF at constant crystallinity. [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B32.00009: Determining the Heat of Fusion and Crystallization Kinetics of Trogamid Bin Mao, Peggy Cebe Trogamid$^{\mathrm{TM}}$ is a high performance semi-crystalline polyamide with optical clarity, chemical resistance and high toughness. It also has much higher glass transition temperature than traditional polyamides, providing excellent thermal stability. We have used differential scanning calorimetry and real-time synchrotron wide and small angle X-ray scattering to study the isothermal crystallization of Trogamid from the melt at crystallization temperatures between T$_{\mathrm{c}} =$ 221 $^{\circ}$C and 233 $^{\circ}$C. Our goal is to correlate the endothermic area from heat flow measurements with the crystallinity index obtained from X-ray scattering, to provide fundamental thermal information about the heat of fusion of Trogamid, which has not been measured to date. Avrami analysis has also been performed over the same temperature range, and been correlated with spherulitic growth rate data obtained from polarizing optical microscopy. For isothermal melt crystallization, the Avrami exponent, n, ranged from 2.13 to 2.23 for T$_{\mathrm{c}}$ from 230 $^{\circ}$C to 233 $^{\circ}$C. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B32.00010: Unusual Temperature Dependence of the Growth Rate of a Bromine Substituted Polyethylene Rufina G. Alamo, Wei Zhang, Laura Santonja, Emine Boz, Kenneth B. Wagener Precisely halogenated polyethylenes are unique polyolefins with a halogen placed on and every ``n'' number of backbone carbons. Contrasting random analogs, precision systems are highly crystalline developing spherulitic morphologies due to a crystallization pattern similar to that of a homopolymer chain. The halogen is accommodated in the crystalline regions as a defect that strains the chain packing proportionally to the van der Waals radius of the halogen. In the present work, we have studied the temperature dependence of the linear growth rates of a bromine substituted polyethylene on each and every 21$^{\mathrm{st}}$ backbone carbon. The linear growth rates display a discrete minimum with decreasing temperature at a crystallization temperature of 64.5 $^{\circ}$C which is reminiscent of the minimum in crystallization rate observed in long chain $n$-alkanes. The spherulitic morphology and overall positive birefringence remains unchanged. The minimum in growth rate is analyzed on the basis of self-poisoning at the growth front resulting from frequent but unstable disordered chains depositions that accommodate the Br atoms. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B32.00011: A Fast Scanning Calorimetric Comparison Study of Crystallization Behavior between Semi-crystalline Polymers and Liquid Crystals Dongshan Zhou, Jing Jiang, Lai Wei, Zhijie Huang, Gi Xue Mesomorphic state with similar liquid crystal order was found to precede the crystallization in many polymers, so the study of nucleation and crystallization from a liquid crystal can provide reference for the study of polymers. The same procedure to study the nucleation and crystallization of semi-crystalline polymers was used to study 4-cyano-4'-octyloxy biphenyl-carbonitrile (8OCB). Different from metastable semi-crystalline polymers of multi-folded chains, whose melting temperature was basically continuously dependent on the crystallization temperature, melting temperature of 8OCB should have definite values, corresponding to disordering of four different polymorphism modifications at 309.0 K, 319.0 K, 325.0 K, and 327.0K, respectively. But, a lower temperature melting peak below 300K was found when 8OCB was annealed at temperature below 250K. More importantly, the peak temperature shifted positively with the increasing annealing temperature, just the same as that of semi-crystalline polymers. At the moment, we were not sure about the structure of the metamorphism and why small molecular liquid crystal showed similar melting behavior that was thought only inherited to chain like semi-crystalline polymers. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B32.00012: Unusual ``Twisting'' Morphology in Poly(3-hydroxybutyrate-co 3-hydroxyhexanoate) and Poly(bisphenol A hexane ether) Spherulites Jerold Schultz Polarized light images of poly(3- hydroxybutyrate-co 3-hydroxyhexanoate) spherulites grown from the melt exhibit the standard evidence of periodic twisting of lamellae. AFM images of lamellae growing from the melt, on the other hand, reveal a sudden change in orientation and a trowel-like morphology. Similarly, AFM images of poly(bisphenol A hexane ether) (BA-C6) lamellae growing from the melt show a sudden orthogonal change of orientation. It is suggested that chain extension in the melt near the propagating front forces the observed reorientation, possibly through creation of crystals with an orientation approximately orthogonal to that of the original crystals. A rudimentary model for this behavior is proposed. [Preview Abstract] |
Monday, March 18, 2013 2:03PM - 2:15PM |
B32.00013: Crystal Pattern and Orientation Structure of Poly Ethlyene Oxide at Surface Qi Liao We try to develop a new morphological method to estimate the orientation structure of polymer crystal at the surface quantitatively. The crystalline structures of PEO single crystals on PVPY substrates were studied in dependence on the degree of supercooling. We show that the diverse patterns could be explained by the difference of crystal orientation. The edge-on and flat-on structure, as well as the patterns in the cross-over states, could give the information of molecular structure. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700