Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A19: Polymer Crystals and Crystallization IFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Christopher Li, Drexel University Room: McCormick Place W-185A |
Monday, March 14, 2022 8:00AM - 8:36AM |
A19.00001: Crystallization and multi-crystalline morphology in PE-b-PEO-b-PCL-b-PLLA tetrablock quarterpolymers and their respective precursors Invited Speaker: Alejandro J J Müller Semi-crystalline block copolymers are fascinating materials. The level of complexity in their crystallization behavior increases with the number of potentially crystallizable blocks in the material. Even though a large body of literature exists on double crystalline diblock copolymers, much less has been published in the cases of triple crystalline triblock terpolymers or tetra crystalline tetrablock quarterpolymers. The morphology and crystallization of novel tetrablock quarterpolymers of polyethylene (PE), poly (ethylene oxide) (PEO), poly (ε-caprolactone) (PCL), and poly (L-lactide) (PLLA) with four potentially crystallizable blocks have been investigated. Their corresponding precursors: triblock terpolymers PE-b-PEO-b-PCL, diblock copolymers PE-b-PEO, and PE homopolymers, were also studied. The direct comparison of the results obtained with DSC, SAXS/WAXS, and polarized light optical microscopy intensity measurements allows to precisely identify the complex crystallization sequence of the blocks upon cooling from the melt. Additionally, it is demonstrated how the self-assembly during sequential crystallization can produce, depending on crystallization conditions, remarkable double, triple, and even tetracrystalline superstructures (i.e., axialites and spherulites). |
Monday, March 14, 2022 8:36AM - 8:48AM |
A19.00002: Critical Tie Molecule Density for Ductility in Linear Polyethylene Seong Hyuk Cho, Richard Register Semicrystalline polymers of low Tg, such as polyethylene (PE), can be brittle or ductile depending on whether sufficient intercrystalline tie chains are present, which depends in turn on molecular weight (M) and crystallization conditions. In linear PEs of narrow M distribution, the strain at break increases steeply over a narrow range of M. However, converting M to a molecular size (melt Rg) and scaling by the solid-state intercrystalline distance (d) fails to collapse the breaking strains for the same PEs crystallized under different conditions (different d); the brittle-ductile transition occurs at smaller values of Rg/d (or equivalently, smaller values of the Huang-Brown tie molecule probability P) for PEs crystallized slowly vs. quenched. Combining these results with literature data for hydrogenated polybutadiene, a lower-crystallinity PE, reveals a strong correlation between the critical value of Rg/d (or P) and the polymer's crystallinity, a behavior strongly mirrored in the yield stress, which increases with crystallinity. The number (or density) of tie chains required for ductility thus decreases strongly with increased crystallinity, as those tie chains become more solidly anchored in less-deformable crystals of higher yield stress. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A19.00003: The role of molecular attributes on crystallization and self-nucleation of conjugated polymers Lucia Fernandez-Ballester, Jesse L Kuebler, Ramin Hoseinabad, Linus Dhapola, Lucia Fernandez-Ballester Mechanical, optical, and diffusive properties of classical semicrystalline polymers are dictated by morphology, which in turn is highly dependent on crystallization conditions and chain molecular characteristics. In the case of conjugated polymers, even small differences in morphology—i.e. crystallinity, orientation, or amount of tie chains between crystallites—can significantly impact transport properties; however, the exact interplay between polymer chain structure, crystallization conditions, and morphology development remains obscured, partly because common solvent processes such as spin coating typically result in ill-defined crystallization conditions. Here, we investigate the role of molecular characteristics on solventless crystallization of poly-3-hexylthiophene under well-defined conditions. The results show that molecular characteristics play a key role in the way crystallization proceeds, and that self-nucleation strategies are effective at manipulating crystallization and morphology but are also highly dependent on molecular characteristics. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A19.00004: Crystallization of Poly(Phenylene Sulfide) Go Matsuba, Genta Mase, Misa Yogiashi, Wenbing Hu Polyphenylene sulfide (PPS) is a super engineering plastic with excellent heat resistance, flame retardancy, and wear resistance. PPS is used for sliding materials and ultra-precision materials because of its characteristics. In recent years, materials with higher performance have been demanded. To clarify crystal morphology and crystallization process in the various annealing temperature, we performed on in-situ small- and wide-angle X-ray scattering and conventional/rapid-scanning DSC measurements. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A19.00005: Liquids that freeze when mixed: Thermodynamics and kinetics of co-crystallization of polyoxacyclobutane with water Emily Barker, Sudesna Banerjee, Tara Meyer, Sachin Velankar Polyoxacyclobutane (POCB) with structure –[CH2-CH2-CH2-O]<sub>n</sub>- has the remarkable ability to cocrystallize with water to form a hydrate. At low molecular weights, simply mixing liquid POCB with water at room temperatures induces freezing. Yet, above the melting point of the hydrate, 37C, and POCB/water mixtures phase-separate into two co-existing liquid phases. This combination of hydrate cocrystallization and LCST-type liquid-liquid equilibrium (LLE) yields a unique of phase diagram. We examine the kinetics of isothermal cocrystallization in mixtures with less than 25 wt% POCB which are homogeneous prior to hydrate formation. The bulk kinetics of hydrate cocrystallization can be well-fitted with the Avrami equation, with the exponent decreasing as temperature increases. The dependence of spherulite growth kinetics on temperature is generally in agreement with the Hoffman-Lauritzen model. Bulk kinetics and spherulite velocities both slow down as the water content decreases far below the hydrate stoichiometry. This suggests that the excess POCB, which cannot crystallize, acts as an impurity. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A19.00006: Molecular Structural Basis in Polymer Melt-Crystallization Toshikazu Miyoshi There are long-standing debates in crystallization mechanism and chain folding structure of long polymer chains from the melt. In this talk we present local chain trajectory of Poly(L-lactic Acid) (PLLA) in extreme conditions, thermodynamically stable crystals formed at a very high temperature from the melt and the glass (cold-crystallization), and a rapidly quenched glass by applying 13C-13C double quantum spectroscopy. The results indicate that i) polymer chains adopt adjacent folding structure even in a glassy state, and ii) adjacent re-entry number in the cold and melt-grown crystals is the same with that in the glass. The newly obtained molecular view in the glassy state proves that chain folding occurs in the pre-stage of crystallization and subsequent crystallization do not induce additional chain folding. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A19.00007: Self-Nucleation Behavior in PEO-b-PCL Copolymers Ryan M VanHorn, Trevor Jonny, Barbara Flores Controlling crystallization in biomedically-relevant block copolymers such as PEO-b-PCL has potential to tailor degradation and drug release properties. Recent studies have shown that the crystallization processes in PEO-b-PCL copolymers are impacted by thermal and casting procedures. Specifically, the crystallization order can be switched due to solvent-polymer interactions during drying. The stability of this unique crystal sequence was analyzed here using self-nucleation studies. Symmetric and asymmetric PEO-b-PCL samples were cast from solvent that induces PEO as the initial crystallizing block. The copolymer's self-nucleation behavior as-cast or from the melt depends on the crystallization order. This technique provides the possibility to tune the crystallinity of each block using post-casting thermal treatment. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A19.00008: Heterogeneous Nucleation in PA66: Efficency of Flow-induced Precursors vs Equivalent Loading of Carbon Nanotubes Alicyn M Rhoades, Anne Gohn, Xiaoshi Zhang, René Androsch, Ralph Colby The nucleating efficiency of a known volume of flow-induced precursors in polyamide 66 (PA66) was established and compared to the nucleating efficiency of a volumetric and surface-area equivalent loading of carbon nanotubes loaded into quiescent PA66. Fast Scanning Calorimetry (FSC) was used to establish critical cooling rates and rotational rheology was used to investigate flow-induced crystallization (FIC). The onset of crystallization time was found to be a function of CNT content, where higher CNT loading reduced the onset time. Above the percolation threshold, CNT nucleation was maximized as quantified by the halftime of crystallization, overshadowing the heterogeneous nucleation that results from FIC. |
Monday, March 14, 2022 10:00AM - 10:12AM Withdrawn |
A19.00009: Tuning the Crystallization Behavior of Block Copolymers with Phospholipid Hybridization Yoo Kyung Go, Cecilia Leal Block copolymer (BCP) self-assembly and crystallization processes can modify their mechanical, optical, and transport properties. Some physical and chemical ways to control BCP self-assembly have been developed over the years. However, studies on modulating the crystallization behavior, particularly crystallite size and orientation, are lacking and remain challenging. In this work, we investigate the use of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipids additives that expand the utility of conventional confinement effects in directing methoxy-poly(ethylene glycol)-b-poly(e-caprolactone) (mPEG-b-PCL) assembly and crystallization on solid supports. mPEG-b-PCL/DPPC hybrid films assemble into multilamellar structures where BCP and lipid layers align in registry throughout the film thickness. DPPC tails and crystalline PCL chains interact at the molecular level: i) DPPC tails un-tilt forming a liquid ordered phase and ii) PCL crystallites re-orient. We suggest that the PCL chains on the fold plane (of orthorhombic lattice) maximize molecular binding with vertically aligned acyl tails of the DPPC by rotating the PCL crystallite by 20 degrees. Our results provide a new approach for switchable crystallization routes of polymeric systems. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A19.00010: Free energy analysis of polymer crystal nucleation indicates cooperative crystallization and nematic alignment Pierre Kawak, Dakota S Banks, Douglas R Tree Despite the prevalence of semicrystalline polymers and their long manufacturing history, the fundamentals of crystallizing a polymer melt are still debated. In particular, recent observations have called into question the validity of classical models of primary nucleation. Several competing newly-proposed models aim to explain these observations by incorporating more polymer features. These near-equilibrium theories behave in accordance with a postulated free energy landscape (FEL). To qualify their applicability, we recently performed calculations of the FEL of oligomer crystal nucleation using advanced Monte Carlo methods. 2D FELs of crystallizing polymers show two basins (equilibrium states), one at low crystallinity and nematic alignment (liquid) and the other at high values of both (crystal). Extracted minimum free energy paths (MFEP) indicate that crystallinity and nematic alignment increase cooperatively during nucleation. We further used the MFEP to extract the nucleation barrier height, which enables calculation of nucleation rates and comparison to experiment. These methods demonstrate quantitative methods for probing nucleation behavior of polymer systems more rigorously, which will aid in validation of future proposed theories and their reconciliation with experiment. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A19.00011: Inversion in the Temperature Gradient of the Crystallization Kinetics of Long-Spaced Polyesters at the Transition Between Two Crystalline Structures Stephanie F Marxsen, Manuel Häußler, Stefan Mecking, Rufina G Alamo We investigate the sharp range of isothermal crystallization temperatures for which a transition between non-integer (thinner) and integer (thicker) layered crystals occurs in long-spaced aliphatic polyesters, and furthermore demonstrate a discrete minimum in the overall crystallization and linear growth rates near the melting point of the non-integer layered crystals. We explain the presence of these minima on the basis of self-poisoning, arising from unstable depositions of non-integer layered chains on the growth surface of integer layered crystals, which dramatically slow the crystallization process. This self-poisoning phenomenon was observed originally in long-chain n-alkanes and low molar mass PEO fractions and has been found more recently in bromine-substituted precision polyethylenes. In this work, we demonstrate that self-poisoning is ubiquitous to high molar mass polymers when transitioning between structures that are not energetically equivalent, and consequently display sufficiently different nucleation and growth kinetics. We thus contribute further evidence to support a polymer crystallization process controlled by segmental deposition events taking place at the crystal growth front. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A19.00012: Linear molecular weight dependence of lamellar aspect ratio in polyethylene Jonathan M Camara Krishnaswamy proposed that the lamellar growth rate of polyethylene was associated with the molecular weight due to chain entanglements. [1] In the Krishnaswamy model the chain diffusion rate to the growing crystal might be proportional to the number of chain entanglements which in turn is proportional to the molecular weight. This kinetic effect should lead to variability in the asymmetry of lamellar crystals in melt crystallized polymers, which could impact the hierarchical growth of fibers and superstructures. However, there is no method to verify this predicted dependence of the aspect ratio for melt crystallized polymers so the proposition has remained conjecture. In this talk, a new hierarchical scattering function, the Unified Born-Green model (UBG), is presented that can quantify the lamellar aspect ratio allowing experimental verification of the Krishnaswamy model. [2] This model also quantifies the local degree of crystallinity within a lamellar stack and two types of disorder in addition to the lamellar thickness. The local degree of crystallinity, when compared to the bulk crystallinity allows for a quantification of lamellar stack clustering. The UBG function can also describe higher order structures such as fibers and mesoscopic crystalline domains for block copolymers. |
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