Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A45: Crystalline Polymers |
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Sponsoring Units: DPOLY Chair: Christopher Li, Drexel University Room: 216AB |
Monday, March 2, 2015 8:00AM - 8:12AM |
A45.00001: Interplay Between a Strong Memory Effect of Crystallization and Liquid-Liquid Phase Separation in Melts of Broadly Distributed Ethylene 1-Alkene Copolymers Rufina G. Alamo, Al Mamun, Xuejian Chen Ethylene-1-alkene copolymers with a broad, bimodal comonomer distribution display acceleration and retardation of the crystallization rate when cooling from a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. The acceleration of the rate is observed in a range of melt temperatures between 165 and 150 $^{\circ}$C, and is due to a strong memory effect of crystallization above their equilibrium melting point. The retardation or inversion of the rate, observed in a range of 150 to 123 $^{\circ}$C, demarcates the onset of a self-seed assisted liquid-liquid phase separation (LLPS) between comonomer-rich and comonomer poor molecules. The interplay between number of self-seeds at the initial melt temperature and chain diffusion during LLPS causes a decrease in the crystallization rate with decreasing melt temperature. When crystallites remain in the melt at temperatures \textless 123 $^{\circ}$C, the crystallization rate again accelerates quickly. The crystallization rates were studied by DSC, and the effect in nucleation density and in overall crystalline morphology of crystallizations from one phase or two liquid phases was followed by polarized optical microscopy and transmission electron microscopy. [Preview Abstract] |
Monday, March 2, 2015 8:12AM - 8:24AM |
A45.00002: Butyl Branch Partitioning to the Crystal Surface in Polyethylenes Detected by NMR Klaus Schmidt-Rohr, Allison White, Kanmi Mao, Diana Smirnova Short-chain branches have pronounced effects on the structure and properties of semicrystalline polyethylenes. Distinct partitioning of butyl branches in high- and linear low-density polyethylenes (HDPEs and LLDPEs) synthesized with hexene comonomers has been detected by solid-state $^{13}$C NMR. In mobility-selective $^{13}$C NMR spectra, distinct signals of mobile amorphous and of trans-rich immobilized branches are observed, the latter with longer $^{13}$C spin lattice relaxation times and limited mobility. This analysis takes advantage of double inverse filtering, which provides the signals of limited-mobility noncrystalline segments selectively. The location of the dynamically constrained branches near the crystal surface has been confirmed by $^{1}$H spin diffusion measurements. The fraction of immobilized butyl branches is approximately constant at about 0.5 mol{\%} for a series of copolymers with 0.35 -- 3.3 mol{\%} hexene. It is close to the percentage expected if one surface site is freely available for each crystalline chain stem. Lower molecular weight appears to enable better ordering of branches at the crystal surface. Further, it more strongly limits a fast-relaxing component in $^{13}$C spin-lattice relaxation of the crystalline signal that can be attributed to chain diffusion. In a HDPE with 0.35 mol {\%} hexene content, nearly all branches are at the crystal surface. [Preview Abstract] |
Monday, March 2, 2015 8:24AM - 8:36AM |
A45.00003: Chain Trajectory of Polymer Chains in Bulk and Single Crystals: Molecular Weight Effect Toshikazu Miyoshi, Youlee Hong Semicrystalline polymers are crystallized as folded chains in thin lamellae of ca. 5-20 nm from random coils in the melt and solution states. Recently, we developed a novel strategy to access chain trajectory of semi-crystalline polymers using $^{\mathrm{13}}$C -$^{\mathrm{13}}$C double Quantum (DQ) NMR combined with selectively isotopic labeling This approach does not suffer from morphology (bulk vs single crystals), molecular weight distribution, and crystallization temperatures. Thereby, DQ NMR has been successfully applied to determination of chain trajectory of semi-crystalline polymer with a relatively low molecular weight in bulk as well as single crystals in wide crystallization temperatures. In this work, we will report chain-folding structure of a semicrystalline polymer with a high molecular weight in bulk as well as single crystals. Molecular weight effects on chain trajectory in different morphology will be demonstrated. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 8:48AM |
A45.00004: SAXS/WAXS measurements of HDPE crystallization during uniaxial extensional flow Erica McCready, Wesley Burghardt We report studies of flow-induced crystallization of high density polyethylene during uniaxial extensional flow. Flow was applied using an SER extensional fixture housed in a custom built oven designed to facilitate in situ synchrotron x-ray experiments. Samples were loaded onto the fixture, heated to well above the melting temperature, and then cooled to the desired crystallization temperature. Extent of crystallization, orientation of crystallites, and extensional viscosity were determined throughout the entire uniaxial extensional flow, using simultaneous small- and wide-angle x-ray scattering (SAXS and WAXS) and torque measurements. Both temperature and extension rate were varied. SAXS patterns show distinct shapes characteristic of shish kebab morphology formation. WAXS peaks indicate high alignment of unit cell structure along the flow direction. Evolution of both SAXS and WAXS patterns can be correlated to each other and to extensional viscosity features during the crystallization process. [Preview Abstract] |
Monday, March 2, 2015 8:48AM - 9:00AM |
A45.00005: Selective crystallization of conjugated polymer nanowires from graphene-coated surfaces Daniel Acevedo Cartagena, Yue Zhang, Elvira Trabanino, Emily Pentzer, Todd Emrick, Alejandro Briseno, Ryan Hayward Solution-based crystallization of conjugated polymers is a promising route to develop hierarchical structures for organic electronic devices, especially solar cells. Well-defined nucleation sites in supersaturated solutions can regulate the crystallization behavior to control the morphology of the material. We have developed an approach to tune the hysteresis between melting and crystallization of poly(3-hexylthiophene) in a marginal solvent, using temperature controlled fractionation. This process produces supersaturated solutions in a metastable state at room temperature, suppressing homogenous nucleation of crystals but allowing for heterogeneous crystallization on nucleation sites. We show that in these metastable solutions, crystalline nanowires are selectively grown on graphene-coated surfaces and highly orientated pyrolytic graphite. [Preview Abstract] |
Monday, March 2, 2015 9:00AM - 9:12AM |
A45.00006: Mesomorphic State in Early Stage Crystallization of Polyethylene Kalman Migler, Angela Hight Walker, Anthony Kotula The kinetic pathway by which a molten polymer transforms into a multi-length scale, semi-crystalline structure upon cooling is an unsolved problem in polymer physics, yet it is critical to the processing, properties and ultimate performance of these materials. Here we utilize Raman spectroscopy to probe the early stage crystallization kinetics of a high-density polyethylene during low undercooling. The importance of Raman as a tool stems from its ability to measure the mass fraction of conformations that are in consecutive trans sequences (locally straight) but are not in an orthorhombic configuration, which we term non-orthorhombic continuous-trans (NOCT). We find that the Raman peaks indicative of NOCT precede the appearance of the peak which indicates orthorhombic crystallinity. We analyze the spectra within the context of a three-state conformational model to extract the mass fractions of the NOCT and the orthorhombic conformational states as crystallization proceeds. Concomitant birefringence and turbidity measurements indicate that this NOCT state can be understood as a separate mesomorphic phase which emerges from the melt state and precedes crystallization. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:24AM |
A45.00007: Morphology and Crystallization Behavior of Poly(3-(2'-ethyl)hexlthiophene) (P3EHT) Containing Diblock Copolymers Emily Davidson, Bryan Beckingham, Victor Ho, Rachel Segalman Poly(3-alkylthiophene) crystallites are confined within classical diblock copolymer microphase separated domains by substituting the alkyl side chain to reduce the crystalline driving force. Previously, we determined that the P3AT chain axis is oriented perpendicular to the domain interface within crystallites. Here, we find that following block copolymer self-assembly in the melt, crystallite growth drives expansion of microdomains, indicating that chains adopt an extended conformation within confined crystallites. In addition, we demonstrate that the degree of perfection of crystallites confined within lamellae may be tuned via the degree of undercooling. [Preview Abstract] |
Monday, March 2, 2015 9:24AM - 9:36AM |
A45.00008: Exploring Molecular Dimension and Trajectory of Polymer Chains Embedded in Single Crystals Youlee Hong, Toshikazu Miyoshi Semicrystalline polymers are crystallized as folded chains in thin lamellae of ca. 5-20 nm from random coils in the melt and solution states.. Even though there are continuous efforts on understanding of crystallization mechanisms at molecular levels for understanding of crystallization mechanism of polymers at molecular levels, the fundamental questions - when, where, and how do semicrystalline polymers fold during crystallization?- have not been clarified due to experimental limitations. Recently, we developed a novel strategy to access chain trajectory of semi-crystalline polymers using 13C -13C double Quantum (DQ) NMR. In this work, we recently investigated determined molecular dimension as well as chain-trajectory of 13C CH3-labeled isotactic poly(1-butene) (iPB1) in form III chiral single crystals blended with nonlabeled iPB1 crystallized under low supercooling, using solid-state NMR. Comparisons of 13C -13C double quantum (DQ) NMR results at multiple sites with spin dynamics simulation revealed individual chains form the three dimensional nanoclusters via folding. This result supports proves two step process of i) cluster formation by chain-folding the prestage of crystallization. and ii) depositions of the cluster on the growth front of single crystal. [Preview Abstract] |
Monday, March 2, 2015 9:36AM - 9:48AM |
A45.00009: On the strain-induced structural evolution upon uniaxial stretching of Poly(VinyliDene Fluoride): influence of secondary crystals and crystalline relaxation Juliette Defebvin, Sophie Barrau, Gr\'egory Stoclet, Jean-Marc Lefebvre Development of more efficient piezoelectric devices tends to innovate and create materials able to combine flexibility and electro-mechanical conversion. Poly(vinylidene fluoride) (PVDF) is a semi-crystalline polymer that exhibits interesting piezoelectric properties. Besides PVDF is able to convert a mechanical solicitation into an electric energy and vice versa. However these physical properties are highly dependent on the polymer crystal structure. PVDF presents at least two main crystalline forms. The most common phase is the $\alpha $-phase that is non-polar. On the other hand, the $\beta $ phase is the most polar one and it can be obtained by a stretching of the $\alpha $-phase. Knowing the influence of the drawing conditions on the strain-induced structural evolution is thus of prime interest. To assess this point the strain-induced structural evolution of PVDF, stretched under different conditions, has been followed in-situ by means of WAXS/SAXS experiments. As a main result, this study shows that drawing conditions strongly affect both the $\alpha $ to $\beta $ phase conversion degree and the crystalline morphology. Moreover the key role played by the crystalline relaxation of PVDF on the strain-induced structural evolution is also highlighted for the first time. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A45.00010: Quantifying tie-chain content in semicrystalline polyolefins with vapor-flow small-angle neutron scattering Amanda McDermott, Chad Snyder, Paul DesLauriers, Ronald Jones Tie molecules bridging adjacent crystalline lamellae in semicrystalline polymers strongly impact mechanical properties, but they remain difficult to characterize. In this work we apply equilibrium swelling theory, balancing the entropic cost of tie-chain extension against the free energy of mixing, to small-angle neutron scattering patterns from semicrystalline polyethylene films whose interlamellar amorphous regions are swollen with deuterated organic solvent. Results show that for a linear polyethylene and several ethylene-hexene copolymers, these vapor-flow SANS measurements of tie-chain content compare favorably with a primary structural parameter (PSP2) that is calculated from molecular architecture and correlates with slow crack growth behavior. [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A45.00011: Isothermal Programming Triple Shape Memory Sergei Sheiko, Jing Zhou, Qiaoxi Li, Sara Turner, Valerie Ashby, Andrey Dobrynin While a variety of shape memory materials have been developed for triple shape memory (TSM), different fixation temperatures are required for memorizing different shapes, with imposed limitations on materials design. We present a new strategy for TSM, where different shapes are programmed at a constant fixation temperature and can be applied to a variety of semi-crystalline elastomers. This universal strategy is based on controlling the interplay between shape-memory thermodynamics and kinetics of polymer crystallization. We have developed a composite model to study correlations between the control parameters (chemical composition, crosslinking density, crystallization rate) and TSM performance (shape fixation and recovery). Furthermore, the isothermal TSM allows one-way reversible shape memory. [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A45.00012: Flow-induced crystallinity in polyethylene as probed by time-resolved Raman spectroscopy and optical microscopy Anthony Kotula, Angela Hight Walker, Kalman Migler The crystallization of polymer melts under flow is critically relevant to the polymer processing industry. Optical, thermal, and mechanical properties of semi-crystalline polymer products depend on the final crystallinity of the material, which depends on the structure and orientation of the initial molecular-scale crystal nuclei formed in flow. Here, we present a combination of optical microscopy and Raman scattering techniques to analyze structure formation in high density polyethylene during steady shear at low degrees of undercooling. When low shear rates ($\sim$ 1~s$^{-1})$ are imposed after a temperature quench to less than 10~$^{\circ}$C undercooling, fibrous structures aligned parallel to the flow direction appear over a period of minutes. Raman spectra indicate that chain straightening (consecutive \textit{trans} chain conformation) precedes the growth of the crystalline phase, and increased shear increases the rate of growth of the consecutive \textit{trans} and crystalline fractions. Complimentary Raman scattering experiments are performed on $n$-alkanes to compare conformational similarities in the molecular structure during the crystallization process. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 10:36AM |
A45.00013: Short-Range Order of Mesomorphic Phase of a Semi-crystalline Polymer by Solid-State NMR: Isotactic Polypropylene Shichen Yuan, Toshikazu Miyoshi Mesophase is intermediate phase between crystalline and melt state. Characterization of short-range structures of disordered mesomorphic phase without long-range order is challenging issue in polymer characterization. The short range order was considered same as $\alpha^{\mathrm{\thinspace }}$or $\beta \quad i$PP, or neither. In this work, a new strategy using $^{\mathrm{13}}$C-$^{\mathrm{13}}$C through space interactions as well as molecular dynamics based on chemical shift anisotropy (CSA) re-orientation is proposed for evaluating short-range order of mesophase of isotactic-polypropylene ($i$PP). $^{\mathrm{13}}$C-$^{\mathrm{13}}$C double quantum (DQ) build up curves of $^{\mathrm{13}}$C 15 percent CH$_{\mathrm{3}}$ selectively labeled iPP and spin dynamics simulations elucidate that local packing structures in mesophase is very close to that in $\beta $ phase. Moreover, exchange NMR proves that the crystalline chains perform large amplitude motions in all $\alpha $, $\beta $, and mesophase. The correlation time of overall dynamics of stems in mesophase follows the same Arrhenius line with that of $\beta $ phase but is largely deviated from the Arrhenius line of the $\alpha $ phase. Through the obtained results, it is concluded that short-range order in mesophase is exceedingly close or same to those in $\beta $ phase. [Preview Abstract] |
Monday, March 2, 2015 10:36AM - 10:48AM |
A45.00014: Stress induced reversible crystal transition in poly(butylene succinate) Guoming Liu, Liuchun Zheng, Xiuqin Zhang, Chuncheng Li, Dujin Wang The plastic deformation mechanism of semi-crystalline polymers is a long-studied topic, which is crucial for establishing structure/property relationships. For polymers with stress induced crystal transition, some open questions still need to be answered, such as on which stage of plastic deformation does the crystal transition take place, and more importantly, what happens on the lamellar structure during crystal transition. In this talk, stress-induced reversible crystal transition in poly(butylene succinate) was systematically investigated by in-situ WAXS and SAXS. A ``lamellar thickening'' phenomenon was observed during stretching, which was shown to mainly originated from the reversible crystal transition. This mechanism was shown to be valid in poly(ethylene succinate). The critical stress for the transition was measured in a series of PBS-based crystalline-amorphous multi-block copolymers. Interestingly, these PBS copolymers exhibited identical critical stress independent of amorphous blocks. The universal critical stress for crystal transition was interpreted through a single-microfibril-stretching mechanism. [Preview Abstract] |
Monday, March 2, 2015 10:48AM - 11:00AM |
A45.00015: Crystallization of low molecular weight atactic polystyrene Yu Chai, James Gilbert, Chad Daley, James Forrest It is well known that atactic polystyrene does not crystallize. However, it is also true that even in pure atactic polymer, there is a small fraction of isotactic and syndiotactic moieties due to random statistics, which are crystallizable. Using small molecular weight atactic polystyrene, we are able to observe crystallization in an acceptable time window. We characterize the crystals in terms of both the morphology and dynamics by using atomic force microcopy and differential scanning calorimetry and the results are consistent with that from the bulk isotactic and syndiotactic polystyrene. As the molecular weight increases, the fraction of pure isotactic and syndiotactic components becomes smaller, and crystallization is not observed. [Preview Abstract] |
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