Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z04: Polymer Crystals and CrystallizationFocus
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Sponsoring Units: DPOLY Chair: Julie Albert, Tulane Univ Room: Room 127 |
Friday, March 10, 2023 11:30AM - 12:06PM |
Z04.00001: Exploring the Effect of Chain Stiffness on the Amorphous Topology of Semicrystalline Polymers Invited Speaker: Chad R Snyder While there are many methods to measure and quantify the structure of the crystalline phase of semicrystalline polymers, our toolbox for quantifying the topology of the amorphous phase is far smaller. Statistical models exist for predicting the topology and have shown good correlation with mechanical properties and some correlation with charge carrier transport in semiconducting polymers, [1] but they rely on assumptions that are not necessarily universal across all classes of semicrystalline polymers. Recently, we presented a method and theoretical framework for quantifying stress transmitters, tie molecules and trapped entanglements, in semicrystalline polymers, which showed good correlation with the statistical models for a system of flexible polymers. [2] Here, we examine the effect of the assumptions of the statistical models and our theoretical framework as they apply to both flexible commodity polymers and semiflexible semiconducting polymers. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z04.00002: Role of processing conditions and molecular attributes on melt-crystallization of conjugated polymers Lucia Fernandez-Ballester, Ramin Hosseinabad, Jesse L Kuebler It is well known that molecular characteristics and processing conditions determine the crystallization process and semicrystalline structure of classical polymers, which in turn dictates their final optical, mechanical, and diffusive properties. For semicrystalline conjugated polymers, charge transport properties are also known to critically depend on semicrystalline structure. However, the interplay between chain structure, processing conditions, and final morphology remains poorly understood because ill-defined crystallization conditions are typically present during solvent processing. Here, we investigate the role of molecular characteristics and well-defined processing conditions on the crystallization process of poly-3-hexylthiophene (P3HT). In particular, we show that the role of molecular weight (Mw) on P3HT crystallization is strongly dependent on regioregularity (RR): crystallization is increasingly hindered with increasing Mw for 90% RR-P3HT but nearly invariant for 95% RR-P3HT. Furthermore, self-seeding processing is more effective in manipulating crystallization of longer, more defective P3HT chains. Overall, this work highlights a key need to report both Mw and RR in P3HT studies. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z04.00003: Dependence of critical tie molecule content on crystallinity for semicrystalline polymers Katherine Gunter, R. A Register Tie molecules - individual polymer chains that quite literally tie together adjacent polymer crystallites - are key to providing structural integrity to semicrystalline polymers. Without such intercrystallite stress transmitters, a semicrystalline polymer will be brittle and unsuitable for most applications. In order to probe the brittle-ductile transition (BDT), we systematically vary the molecular weight, crystallinity, and domain spacing of hydrogenated polynorbornene homopolymers, hPN, and hydrogenated norbornene-hexylnorbornene random copolymers, hP(N-r-H). How these factors affect tie molecule fraction (as calculated by the Huang and Brown model) is also investigated and correlated with brittle/ductile fracture. We find crystallinity to be a major factor in predicting critical tie molecule content (the fraction of tie molecules needed to reach the BDT); a factor of 2 increase in crystallinity reduces the fraction of tie molecules at the BDT by an order of magnitude. Comparing these data with those from linear polyethylene homopolymers (LPE), we find similar trends in both cases, but for identical crystallinities, the critical tie molecule content is lower by nearly an order of magnitude for hPN than LPE. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z04.00004: End group effect on poly(L-lactic acid) crystal Shichen Yu, Seyong Kim, Christopher Y Li Following translational symmetry in crystal growth is one of the most fundamental laws in crystallization. Numerous polymer crystals with broken translational symmetry however have been observed, including helicoidal, tubular, and spherical crystals. Herein we report a new group of single crystals that has broken translational symmetry. Scrolled α-form poly(L-lactic acid) (PLLA) crystals are grown via solution crystallization. PLLA is end-functionalized with different types of end groups study the end-group effect on the crystallization process. The single crystal gradually scrolled into a hollow cylindrical structure along a specific axis of crystals. Selected area electron diffraction shows the scrolling axis of single crystals is along the fastest crystal growth direction. The bending of original 2D lamellae of single crystals is attributed to the unbalance surface stress of the lamellae. The end groups’ effect on crystal morphology is discussed in the solution crystallization regime. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z04.00005: Processing-structure-property relationships during uniaxial rolling and subsequent tensile drawing of polyolefin cast films and composites Dayne A Plemmons, Joseph L Lenhart, Randy A Mrozek Extreme plastic deformation in semi-crystalline polyolefins is facilitated by chain mobility in the crystalline fraction. The temperature at which such motion is activated – the alpha-transition temperature (Tα) – and the nature of such motion (e.g. torsional chain-slip) depends heavily on chain conformations within lamella and near crystalline interfaces. Accordingly, processing history can have cascading effects on structural progression during orientation of extruded films. Here, we examine multi-stage structure-property relationships during the solid-state orientation of polyethylene films. The thickness of the films is first reduced by uniaxial rolling at temperatures below the melting point. Next, the rolled films are tensile drawn at elevated temperature. In the first stage, deformation primarily occurs through modification of the as-extruded spherulitic structure. DMTA measurements indicate that the intermediate structures resulting from rolling at different temperature have varying Tα. In the tensile drawing stage, the total orientation and mechanical properties are largely dependent on the proximity of the drawing temperature to Tα; far below Tα deformation is substantially elastic, while far above Tα deformation is localized due to poor stress transmission. Independent of rolling temperature, the most effective orientation occurs when the drawing temperatures are near the onset of the alpha-transition as identified by linear thermal expansion measurements. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z04.00006: Grafting density effect on the crystallization behavior of molecular brushes Jeffrey T Wilk, Carl Furner, Michael Kelly, Christopher Y Li, Bin Zhao Molecular bottlebrushes are a class of grafted block-copolymer containing polymer chains grafted to a semi-flexible backbone. Of particular interest are molecular bottlebrushes containing semicrystalline side chains. In such systems, the grafting density of tethered side chains will significantly influence the development of the final crystalline phase. To investigate this effect in more detail, a series of poly(2-hydroxyethylmethacrylate)-g-poly(ethylene oxide) (PHEMA-g-PEO) bottlebrush polymers were synthesized via a copper catalyzed azide-alkyne cycloaddition reaction. Crystallization behavior, investigated through non-isothermal and isothermal differential scanning calorimetry (DSC), displayed a general increase in crystallization and melting temperature as grafting density increases, suggesting the defect contribution of the backbone is alleviated through increased chain packing. Crystal morphology was investigated through scanning electron microscopy, atomic force microscopy, and polarized light microscopy. Morphological investigations suggest architecture effect on nucleation and radial growth of formed spherulites. This work provides an overview on how grafting density can affect the crystallization behavior of molecular brush systems and provides a framework for future development for semicrystalline brush copolymers. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z04.00007: Free Energy Analysis of Crystal Nucleation of Semiflexible Polymers Douglas R Tree, Pierre Kawak Despite the prevalence of semicrystalline polymers and their long manufacturing history, there are still many fundamental questions surrounding the process of crystallization in a polymer melt. Specifically, recent simulations and experiments have called into question the validity of classical theories of the nucleation process. Emerging competing theories postulate the existence of stable or metastable intermediates, including nematically aligned states. We look more closely at the crystallization of polymers in a melt using advanced Monte Carlo methods such as Wang-Landau sampling and expanded ensemble density of states. Specifically, we explore the nucleation behavior of a family of models of semiflexible oligomers and use these methods to compute phase diagrams, free energy landscapes, and minimum free energy paths. Consistent with emerging theories, we find that models with continuous potentials have a universal phase diagram that contains an intermediate nematic phase that mediates nucleation. However, models with discontinuous potentials have a cooperative phase transition that does not have an intermediate nematic phase. These results further our understanding of crystal nucleation of polymers and improve our ability to compare molecular simulations to experiment. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z04.00008: Nonisothermal Melt Crystallization Behavior of Semicrystalline Polymers Monitored Using an In Situ Fluorescence Technique Kailong Jin, Richard G Nile, Maya Cabello Upon cooling a semicrystalline polymer from its amorphous melt state, it undergoes nonisothermal crystallization through nucleation and crystal growth. Understanding the nonisothermal crystallization kinetics of a semicrystalline thermoplastic is key to tuning its crystallinity, microstructure, and material properties. Conventional spectroscopic, calorimetric, and rheological techniques have been used for studying nonisothermal crystallization, but they are limited in sensitivity, tunability, and availability. Our group has developed a new fluorescence technique for sensing semicrystalline polymers’ melting transitions by incorporating fluorescent probes into polymer matrices. Herein, this methodology has been extended to study nonisothermal crystallization by monitoring the T-dependent fluorescence intensity of a dye-labeled polymer. As crystals form upon cooling from the melt state, the intramolecular motions of fluorophores are restricted and thus their T-dependent fluorescence intensity data exhibit a stepwise increase during crystallization. The crystallization processes monitored by fluorescence agree well with those measured by conventional differential scanning calorimetry. Moreover, fluorescent labeling could enable novel location-specific studies on the local crystallization within heterogeneous polymeric systems (e.g., multilayer films), which are out of reach for most conventional techniques that measure spatially averaged properties. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z04.00009: The origin of piezoelectricity in ferroelectric polymers Lei Zhu One important property of ferroelectric polymers is their piezoelectricity. Despite decades of research on piezoelectric polymers, the origin of polymer piezoelectricity is still unclear. Combined with the fact that their piezoelectric performance is much worse than the ceramic counterparts, such as barium titanate and lead zirconate titanate, this has hampered the development of high-performance piezoelectric polymers and their practical applications. Recently, we have discovered that the complex semicrystalline structure of ferroelectric polymers plays an important role. Namely, the electrostriction of the oriented amorphous fraction (OAF), which links between the primary crystalline lamellae and the isotropic amorphous fraction (IAF), is the origin of piezoelectricity of ferroelectric polymers. In addition, if relaxor-like secondary crystals can further grow in the OAF, the piezoelectricity will be further enhanced. For example, we have achieved high piezoelectric coefficients (both d31 and d33) in the range of 60-80 pC/N for poly(vinylidene fluoride) and its random copolymers with trifluoroethylene. This understanding will help us design new ferroelectric polymers with even higher performance and better applications. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z04.00010: Shear-Induced Crystallization in Polyethylene/Polypropylene Blends McKenzie L Coughlin, Derek Huang, Anthony P Kotula, Kalman B Migler The two most abundant single-use plastics are polyethylene (PE) and polypropylene (PP), contributing to the largest share of the plastics waste stream. PE/PP blends, created as a solution to separation issues in recycling, are often brittle due to their immiscibility and the resulting micro-separated domains that crystallize separately upon cooling. The crystallization behavior of PE/PP blends during processing controls the overall mechanical properties but is poorly understood. In this work, the crystallization and rheological properties of high-density polyethylene and isotactic polypropylene blends are studied using a combination of the rheo-Raman microscope, differential scanning calorimetry, and electron microscopy. In particular, we examine the impact of shear, blend morphology and composition on the crystallization kinetics, and how the resulting semicrystalline microstructure influences the rheological properties of the blend. We find unexpected composition dependence to the shear-induced crystallization behavior of the polypropylene which we attribute to domain structure and micro-flow fields. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z04.00011: Perspectives of Molecular Structure, Dynamics, and Morphology for Sustainable Semicrystalline Polymers Navin K Kafle Most semicrystalline polymers are incompatible with each other. Therefore, recycling and upcycling commercially available semicrystalline polymers (e.g., polyethylene and polypropylene) are challenging. This is one of the biggest issues in polymer science and polymer engineering. In this talk, I present unique examples of stereoregular and irregular hydrogenated poly(norbornene) (hPNB)s1 and their blends2 for sustainability. Based on unprecedented structures and molecular dynamics of hPNBs and their blends, I will provide a strategy designing novel semicrystalline polymers for next generations. |
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