Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F06: Semicrystalline Polymers and Polymer Blends |
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Sponsoring Units: DPOLY Chair: Julie Albert, Tulane Univ Room: LACC 153A |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F06.00001: Electrostatic Forces-Induced Transformation of an Atactic Polymer from Amorphous to Semicrystalline Chinomso Nwosu, Edward Coughlin Quaternization of P4VP by alkyl halides with varying number of carbons (n = 1 – 12) presents a platform to study the interplay between electrostatic attractive and steric repulsive forces. In P4VP-based random copolymers, the competition between these forces results in two distinct short-range ordering: ion clusters and backbone-to-backbone spacing. For copolymers quaternized with methyl or ethyl halides (n = 1 – 2), dipole forces are dominant forming ion clusters; while for copolymers quaternized with longer alkyl halides (n = 3 – 8), steric repulsion is dominant resulting in backbone-to-backbone spacing. The competition between electrostatics and sterics also governs the morphology of quaternized P4VP homopolymer. Unlike in the copolymers where clusters of ions are formed when dipole forces are dominant, for P4VP_CnI and P4VP_CnBr, the atactic amorphous microstructure is transformed into an atactic semicrystalline. Characterization of P4VP_C2I and P4VP_C2Br by WAXS show distinct Bragg peaks of a primitive simple cubic structure with possible polymorphism.Thermal analysis shows double melting endotherms with a single recrystallization exotherm. Macrostructures of samples probed by POM show that crystals upon nucleation can grow into spherulites or dendrites. |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F06.00002: Chain Conformation, Packing, and Folding Structures of Poly(L-Lactic Acid) in Glassy State as Studied by 13C Solid-State NMR and Selective Isotope Labeling Shichen Yuan, Toshikazu Miyoshi Deep quenching of semi-crystalline polymer from the melt state down to below glass transition temperature results in the glassy state. Comparing with the melt grown process, the cold-crystallization of glass samples usually exhibit a much higher overall crystallization rate, which triggers numerous investigation of the glassy state. The short-range-ordered nature of polymer in the glassy state poses difficulty in analyzing the chain conformation, packing and folding structure by conventional characterization techniques. Here, we synthesized 13C single and double sites labeled PLLA and investigated the structures of the glassy sample in detail. It was demonstrated that the conformational/packing/folding structures are quite similar between glassy and crystalline states. This result suggests that even rapidly quenched glassy sample possess the same local structure as the crystalline form. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F06.00003: SAXS/WAXS Studies of Flow-Induced Crystallization of LDPE under Uniaxial Extensional Flow Mu Sung Kweon, Wesley Burghardt We report flow-induced crystallization studies of LDPE under uniaxial extensional flow. Flow was applied using an SER housed in a custom-built oven designed to facilitate in situ synchrotron x-ray experiments. Samples loaded onto the fixture were first heated well into the melt, and then cooled to selected crystallization temperatures under which negligible quiescent crystallization occurred on reasonable time scales. Two types of flow protocols were employed: short-term and continuous. Under short-term flow, a short burst of flow was applied at temperatures where samples crystallized isothermally after the application of flow under varied extension rates and Hencky strains. Under continuous flow, samples crystallized isothermally at selected temperatures during the application of flow under varied extension rates. The extent of crystallization and orientation of crystallites were monitored using SAXS and WAXS measurements. WAXS measurements are generally consistent with each other and indicate alignment of unit cells along the flow direction in both short-term and continuous flows. SAXS patterns under short-term flow show diverse and complex evolutions in the lamellar scale morphologies; those under continuous flow show distinct features of shish-kebab crystalline structure. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F06.00004: Effect of Ultra-High Molecular Weight Chain On Flow-Induced Crystallization of Polymers Bo Shen, jeremy wei, Julie Kornfield Under shear flow, the morphology of crystalline polymers changes dramatically, leading to the formation of a unique structure known as the “shish-kebab.” The mechanism of shish formation has been under debate for decades. The current belief of shish formation is followed by a two-step mechanism: point nuclei is formed first and followed by shish growing from it, also researchers realizes concentration of high molecular weight chains in the shish is the same as in the bulk. Besides these progress, mechanism at molecular level is still not clear and few molecular theory is given to explain why high molecular long chains greatly enhance the shish formation. Methods such as in-situ X-ray scattering, microscopy, and rheology suffer from relatively poor time resolution, making birefringence a very powerful and complementary tool to study what happens during flow. We investigated the flow behavior of a series of polyethylene blends with different lengths and concentrations of ultra-high molecular weight chains using birefringence and rheology measurements. We found that even with very low concentration, birefringence response is different, which reflects the chain configuration during flow and leads to different final morphology. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F06.00005: Abstract Withdrawn
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Tuesday, March 6, 2018 12:15PM - 12:27PM |
F06.00006: Modelling Viscoelastic Response in Semicrystalline Polymer Fibers Aakash Sharma, Guruswamy Kumaraswamy, Shirish Thakre Polymer fibers are ubiquitous in Nature and find widespread applications in industry. Fiber mechanical properties are critical to their application and to product quality. Models for the mechanical properties of fibers that can capture their behavior in different deformation experiments, over a wide range of temperatures and that relate these properties to the fiber microstructure are currently lacking in the literature. We present a model that can accurately capture the mechanical behavior of semicrystalline fibers. We demonstrate that the moduli from model fits compare well with the crystalline and amorphous phase moduli from WAXD and vary with temperature in a physically realistic manner. The model relaxation timescales for semicrystalline/glassy fibers follow the TNM-KAHR temperature dependence. Our findings indicate that the qualitative features of the fiber mechanical properties are independent of microstructural details, and only require crystal/amorphous coexistence. Our model is also able to capture the mechanical response of several other non-equilibrium systems including biological cells, microgel pastes etc. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F06.00007: Angle-resolved In-Plane Thermal Anisotropy of Semi-Crystalline Polyethylene Films using Transient Grating Andrew Robbins, Austin Minnich Crystalline polymers are of keen interest due to their potential as low density thermal conductors. However, obtaining measurements of in-plane thermal conductivity and anisotropy needed to inform synthesis strategies remains challenging. Here, we report measurements of the in-plane thermal anisotropy of semi-crystalline polyethylene films using transient grating (TG) spectroscopy. Our measurements indicate a marked in-plane thermal anisotropy of around 50 in solution-processed aligned polyethylene films and an unusual angle-dependent thermal conductivity in biaxially stretched films. Our results provide insight into the microstructure and thermal transport properties of molecular thermal conductors that can be used to realize molecular solids with exceptionally high thermal conductivity. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F06.00008: Microscopic origin of plastic deformation in semicrystalline polymers Sara Jabbari-Farouji, Joerg Rottler, Olivier Lame, Michel Perez, Jean-Louis BARRAT The mechanical properties of polymeric materials strongly depend on their morphology and spatial arrangements. We examine the microscopic origin of the non-linear tensile response in amorphous and semicrystalline polymers by performing large-scale molecular dynamics simulations of various chain lengths [1,2]. Computing ratio of microscopic stretch of the polymers relative to the macroscopic stretch, we find that the semicrystalline polymers deform less affinely than their amorphous counterparts. Investigating the microscopic rearrangements of the polymers during tensile deformation, we show that the intercrystalline chain connections known as tie chains contribute significantly to the plastic response in the strain-hardening regime [2]. Our results suggest that the mechanical behavior of semicrystalline polymers is controlled by two interpenetrated networks of entanglements and tie chains. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F06.00009: Production and analysis of highly monodisperse oligomeric Polyethylene Oxide Junjie Yin, Adam Raegen, Zhu Shipei, James Forrest Synthesized polymers contain a distribution of different molecular weights. Even the most monodisperse synthetic polymers usually available have a polydispersity index (PDI) of about 1.01. Even these relatively monodisperse samples contain many different polymer chain components (N-mers). In this study, we produce highly monodispersed Poly(Ethylene oxide) through evaporative purification of a Mn 600 PEO sample with a relatively high PDI. The purified samples were studied with TOF-MALDI, differential scanning calorimetry (DSC), and optical microscopy. While the original polymer has a Tm of 294K, the melting temperature of separated products ranges from 265K to 296K. The Tm values are compared with Gibbs-Thompson predictions where the crystal size is determined by the number of monomers. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F06.00010: Fluctuation correction for the critical transition of symmetric homopolymer blends Tom Beardsley, Mark Matsen Monte Carlo simulations are performed on structurally symmetric binary homopolymer blends over a wide range of invariant polymerization indices, Ñ. A finite-size scaling analysis reveals that certain critical exponents deviate from the expected 3D-Ising values as Ñ increases. However, the deviations are consistent with previous simulations and can be attributed to the fact that the system crosses over to mean-field behavior when the molecules become too large relative to the size of the simulation box. Nevertheless, the finite-size scaling techniques provide precise predictions for the position of the critical transition. Using a previous calibration of the Flory-Huggins interaction parameter, χ, we confirm that the critical point scales as (χN)c = 2 + cÑ-1/2 for large Ñ, and more importantly we are able to extract a reliable estimate, c ≈ 1.5, for the universal constant. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F06.00011: Modeling hydrogen bonding in polymer blends using association models Debadutta Prusty, Victor Pryamitsyn, Monica Olvera De La Cruz We present a model to study the phase behavior of polymer blends with hydrogen bonding interactions. In our model, hydrogen bonding groups in A homopolymer and B homopolymer are modeled as sticker groups capable of both self-association and inter-association. We derive an expression for the free energy of such a system in the mean field limit. We use this expression to construct phase diagrams of the blend and explore the effect of strengths of inter-association and self-association, fractions of hydrogen bonding stickers and asymmetry in sticker fractions. Our model is different from the tradtional Flory approach in which a constant negative χ parameter is used to model hydrogen bonding interactions in that our model produces a concentration dependent χ parameter for hydrogen bonding interactions. We subsequently incorporate our model into self-consistent field theory of blends and using it, examine the properties of the A-B interface. We observe that when the net interaction strength between dissimilar stickers is significant, our model predicts lower interfacial tension and a more diffused interface than Flory model with an effective χ parameter corresponding to the same phase boundaries. We rationalize the above observation by analyzing the free energy curves of both models. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F06.00012: Spectroscopic Investigations on Polystyrene-Polyvinylidene Fluoride Nanofibers Maximiliano Villarreal, Karen Lozano, Dorina Chipara, Mataz alcoutlabi, James Hinthorne, Mircea Chipara Polystyrene-Polyvinylidene Fluoride (PS-PVDF) nanofibers have been obtained by force spinning. To achieve this goal, the two homopolymers have been dissolved in a common solvent (dimethylformamide). The obtained solution was homogenized by stirring at about 1,000 rpm for several hours, followed by a 30 minutes sonication. The homogeneous solution was force spun at room temperature, in the air, at various spinning rates ranging from 1,000 rpm to 10,000 rpm. Nanofibers of PS-PVDF blends containing various fractions of PVDF (ranging between 0 and 60 % wt.) have been obtained and collected as mats. The obtained mats were investigated by Raman spectroscopy and Wide-Angle X-Ray Scattering. The presence of both homopolymers has been confirmed. The distribution of the nanofibers diameters and their dependence of spinning rate, solution concentration, and PVDF fraction was derived from microscopy studies. Energy Dispersive Spectroscopy was used to generate a map of fluorine atoms and to better understand the morphology of these nanofibers. Additional contact angle measurements have been performed. The range of solutions' concentrations and PVDF fractions for which submicron polymer blend fibers have been obtained will be discussed in detail. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F06.00013: A Simulation Method for the Phase Diagrams of Polymer Blends Hyuntae Jung, Arun Yethiraj Computer simulations are a powerful tool for establishing the relationship between molecular interactions and the phase behavior of polymer blends. Phase diagrams are usually obtained from molecular simulations via the Gibbs Ensemble method with the absense of interfaces between phases. The method has challenges for polymers because chain insertion has a very low acceptance probability. Another approach is to simulate a system with an interface; the challenge here is that the interface moves during the course of the simulation making it difficult to estimate the coexisting concentrations (or densities). In this work we propose a method where the concentration profiles at different time slots are aligned by identifying the interface in each time window using a spatial density autocorrelation function. We validate the method by calculating the phase diagrams of the Widom-Rowlinson model and symmetric blends of freely-jointed polymers, and comparing to previous Gibbs ensemble simulations. We use the method to calculate the phase diagram of poly(ethylene oxide) in the ionic liquid BMIM BF4. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F06.00014: Crimping induced structural transformations explain lasting strength of bioresorbable vascular scaffolds during hydrolysis Karthik Ramachandran, Artemis Ailianou, Mary Beth Kossuth, James P Oberhauser, Julie Kornfield Bioresorbable vascular scaffolds (BVSs) are a promising new treatment for Coronary Heart Disease (CHD), one of the leading causes of death in the world (~7 millon/year). The first clinically approved BVS is made from poly L-lactide (PLLA), which hydrolyzes to L-lactic acid, a metabolic product processed by the body. Unlike permanent metal stents, “transient” BVSs support the occluded artery for 3-6 months, but are completely resorbed in 2-3 years, leaving behind a healthy artery with no risk of Late Stent Thrombosis. The clinical success of BVSs is surprising given the inherent brittleness of PLLA – the scaffold survives extensive deformation during crimping (>50%) and upon subsequent deployment in the artery. Using X-ray microdiffraction, we discovered that crimping creates a multiplicity of morphologies in the BVS; crystallites change orientation from the radial to the hoop-direction over distances of 100µm. This unique morphology facilitates a low-stress response upon deployment, protecting the scaffold from fracture and imparting the strength needed to support the artery. Therefore, the BVS takes advantage of structural transformations during crimping to exhibit ductile character upon deployment. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F06.00015: Radial Dependence of Film Formation During the Spin-coating of an Immiscible Polymer Blend Eleanor Dougherty, Mark Geoghegan, Matthew Mears The mixing of polymer blends is thermodynamically unfavourable and phase separation can often be observed in the morphology of spin-coated polymer blend films. Little work has been undertaken in determining the radial dependence of the spin coating process. In situ light scattering experiments before and method has been extended to explore how the effect varies radially at 0, 4, 8, and 12 mm from the centre of the film for solutions of 2% and 4% polymer concentration by mass for spin-coating at 1000 and 2000 rpm. It is shown that there is a significant radial dependence to the film formation. Inertial forces initially govern spin-coating until solvent evaporation becomes dominant. The turbulent forces change with radius and thus vary the evaporation rate with radius, resulting in a radial variance. These results are discussed in terms of applicable models. |
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