Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V55: Polymer Crystallization III: Copolymer Crystallization, Intercrystalline Topology and Mechanical PropertiesFocus
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Sponsoring Units: DPOLY Chair: Wenbing Hu, Nanjing University Rufina Alamo, Florida A&M and Florida State University Room: BCEC 254B |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V55.00001: Statistics of Ties and Loops in Amorphous Regions of Polymer Crystals Sabin Adhikari, Murugappan Muthukumar Polymer crystals grown from melt consist of alternating lamellar crystalline regions and amorphous regions. We study the statistics of ties and loops in the amorphous region. Mechanical properties of crystalline polymers are highly dependent on the relative populations of ties and loops in the amorphous regions. We develop a statistical mechanical formulation to calculate the conformational entropy of ties and loops with consideration of finite chain length and possible association of a chain with multiple lamellae. Results of our numerical calculations show that, the fraction of the tie population relative to loops increases with increasing chain length, and it decreases with increasing the interlamellar separation and the lamellar thickness. The average number of lamellae connected by a chain is also calculated. It is also found to increase with increasing the chain length and to decrease with increasing the amorphous thickness. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V55.00002: Tie Molecule Formation in High Density Polyethylene Seong Hyuk Cho, Richard Alan Register The mechanical toughness of a semicrystalline polymer, such as polyethylene (PE), originates from tie molecules: polymer chains that span two or more crystalline lamellae. During rapid crystallization, polymers cannot disentangle, so tie molecules form when the size of the polymer coil in the melt, controlled by its molecular weight (M), exceeds the intercrystalline spacing (L) in the solid state, governed by the specimen’s crystallization history. Prior studies have yielded some insight into the brittle-to-ductile transition in PE as M is increased, but often for broadly-distributed PE with no measure of L. Here we synthesize a series of narrowly-distributed (dispersity < 1.2), perfectly linear (high density) PEs with targeted M using ring-opening metathesis polymerization of cyclopentene followed by hydrogenation. PEs were either quenched or slow-cooled to vary crystallinity (0.65 - 0.85) and L, measured by differential scanning calorimetry and small-angle x-ray scattering. We investigate the brittle-to-ductile transition of PE by uniaxial tensile testing in relation to its M, end-to-end distance in the melt, and L, and find a relatively abrupt transition in these narrow-distribution PEs. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V55.00003: Does crystal thickness dictate yield kinetics in polyethylene? Jevan Furmanski, Jonathan Schaefer, Leon Govaert, Hans Van Dommelen There has been a longstanding effort to predict the resistance to plastic deformation of polyethylene via crystal plasticity-based micromechanical modeling, deriving the plasticity kinetics from the assumption that the strain carrier is a screw dislocation. This leads to the notion that the yield kinetics are dominated by crystal thickness, or more precisely the chain stem length within the crystal. There is in general a high degree of correlation between the crystallinity and crystal thickness, making it difficult to distinguish between these two microstructural attributes as the driving variable for plasticity. A wide range of crystallinity and stem lengths was obtained by varying crystallization via both cooling rate and various concentrations of short-chain branching, permitting the disentangling of stem length from crystallinity. The rate- and temperature-dependence of yield strengths were fit to a two-term stress-activated Ree-Eyring model. Chain stem length was measured via the Longitudinal Acoustic Mode in low wavenumber Raman spectroscopy. With this material series it was shown that crystallinity drives yield kinetics, rather than stem length. These insights will be placed in the context of a micromechanical model employing stress-activated crystal slip kinetics. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V55.00004: Structure and morphology of poly(ethylene)-block-isotactic poly(propylene) di-block copolymers Claudio De Rosa, Rocco Di Girolamo, Anna Malafronte, Finizia Auriemma, Miriam Scoti A study on the structure and morphology of crystalline di-block copolymers (BCP), composed of stereoregular crystallizable polyolefins is presented. In particular, we report a structural characterization of di-block copolymers formed by crystalline PE block linked to crystalline isotactic polypropylene (iPP) block of different block lengths. The dependence of the thin film BCP morphology on the sequential crystallization from the phase separated melt of the crystallizable blocks has been investigated. The BCPs have been epitaxially crystallized onto crystals of a substrate to achieve a better control over the crystallization. Ordered nanostructures where the two blocks are organized in separated alternating lamellar domains guided by the orientation of the crystalline lamellae are obtained. We demonstrate that, tuning the block length and using a specific substrate, it is possible to control the crystallization process and obtain large-sized, well-oriented lamellar microstructures with long range order achieved over the area in contact with the crystalline substrate. Possible applications of these nanostructures are discussed. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V55.00005: Quiescent and flow-induced crystallization of polyolefins studied by a novel low-field RheoNMR combination Karl-Friedrich Ratzsch, Volker Räntzsch, Begüm M. Özen, Manfred Wilhelm Combining NMR and rheology has received great attention in the past, as it allows studying the interdependence of macroscopic and molecular properties of soft matter, e.g. polymers, liquid crystals or colloids. Flow profiles (e.g. steady or oscillatory shear) both in the linear and non-linear regime can be applied to monitor and also to modify the (time) evolution of sample properties. Most RheoNMR designs have been realized for high-field NMR spectrometers using only simple shear cells. Here we present a low-field RheoNMR set-up based on a portable 30 MHz NMR unit that was integrated into a commercial strain-controlled rheometer. This unique combination can be employed to simultaneously conduct a full rheological characterization while monitoring molecular dynamics in-situ via 1H TD-NMR. Possible applications include the measurement of quantitative composition in crystallizing soft matter (fats, polymers, etc.) and multiphase systems during the application of shear protocols. To display the possibilities of this new technique, studies on the quiescent and flow-induced crystallization of polyolefins are presented. A short time steady-shear protocol was applied to study flow-induced crystallization as a function of different temperatures and flow conditions. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V55.00006: Distribution of Chain Ends in a Crystal-Fixed Polymer Elucidated by Solid-State NMR Shichen Yuan, Klaus Schmidt-Rohr The location of chain ends in the morphology of semicrystalline polymers has recently received renewed attention. In particular, chain ends at the crystal surface can help avoid density anomalies in the noncrystalline surface layers.1 Here we present a detailed analysis of the distribution of chain ends across the ~ 15 nm repeat unit of semicrystalline poly(ε-caprolactone) (PCL)2, a crystal fixed polymer3 of moderate crystallinity. An excellent signal-to-noise ratio and spectral resolution is achieved by isotopic labeling of chain ends via conversion of OH end groups with 13COO-acetyl groups. Through distinct (an)isotropic chemical shifts and relaxation times, one can distinguish chain ends in the crystaline, interfacial, and amorphous layers. 56% of the chain ends are found in the core amorphous layers, which exceeds the amorphous core fraction. About 20% are immobilized in the crystal lattice; many of these segments are found near the interface, according to fast 1H spin diffusion from the amorphous core layer. |
Thursday, March 7, 2019 3:42PM - 4:18PM |
V55.00007: The effect of multi-block structure on the crystallization and properties of ethylene/1-octene copolymers from chain shuttiling technology. Invited Speaker: Finizia Auriemma The crystallization properties, the morphology at nanometric length scale and the tensile properties of ethylene/1-octene multi-block copolymers (EOBCs) obtained from chain shuttling technology are analyzed. The samples are characterized by a statistical multi-block architecture, where soft and amorphous blocks with high octene concentration (≈18.9mol%) alternate with hard and crystalline blocks with low octene concentration (≈0.5mol%). A set of samples with similar octene concentration in the hard and soft blocks, fraction of hard blocks and melting temperature of ≈120°C, but different average length of the blocks and average number of blocks/chain are selected. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V55.00008: Contrasting melt memory of homopolymers and random ethylene copolymers using halogen substitution with precision placement or random distribution Stephanie Marxsen, Rufina Alamo Polyethylenes with Cl or Br atoms placed at an equal distance of 21 or 15 backbone carbons are known to crystallize as homopolymers, accommodating the halogen in layered crystallites. In contrast, analogs with a random distribution display a crystallization path dominated by sequence-length selection. A consequence of the sequence selection of random copolymers is a constrained interlamellar region and broader melting peaks displaced at higher temperatures than systems with the precise placement. Precision and random ethylene-vinyl halides are excellent models to contrast the strong melt-memory behavior observed in random ethylene 1-alkene copolymers with lack of melt-memory seen in linear polyethylene. While precision polyethylenes with Cl or Br placed on each 21st or 15th backbone carbon show negligible deviation in crystallization rate above the observed melting, the increase in crystallization rate of analogs with the random distribution is observed even from melts 60 degrees above the observed melting point. These data give further evidence of the sharp difference of melt-memory behavior between homopolymers and random copolymers. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V55.00009: Study on the Thermodynamics of Polymer Crystallization Based on Twin-Lattice Model Nuofei Jiang Polymer crystallization is the most important part in determining the performance of polymeric materials. The twin-lattice model originally provided by Lennard-Jones and Devonshire, developed by Pople and Karasz and other researchers, is extended for describing the thermodynamics of polymer crystallization. The positional order of segments and the orientational order of bonds are considered in this model. The free energy of polymers is obtained by further introducing the conformational energy and entropy. We studied two kinds of processes in polymer crystallization, including the process with plastic crystal phase and without any mesophases. The choice of crystallizing process is determined by the magnitude of lattice energy and conformational energy. Considering data reliability, n-paraffins are chosen as the representation of polymers to compare the predictions of the model with experimental observations. We predict the number of carbons beyond which the rotator phase disappears, which is quite in agreement with the experiments. These calculations and results show this model can provide a new understanding to the crystallization of polymers. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V55.00010: Crystallization Process with Aggregation of Small Crystallites for Polytrimethylene Terephtharate Takashi Konishi, Daisuke Okamoto, Daisuke Tadokoro, Yoshitaka Kawahara, Koji Fukao, Yoshihisa Miyamoto Polymer crystallization mechanism has explained the crystal nucleation and growth mechanism, while the existence of density fluctuations during the initial stage of crystallization has been discussed. In order to clarify the density fluctuations, the isothermal crystallization from the melt state of poly(trimethylene terephthalate) (PTT) has been studied by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Large scattering intensity in the low-q region (IL(q)) has been observed by SAXS during the early stage of crystallizations. IL(q) increases with time, reaches a maximum, and decreases. The results revealed the crystallization mechanism in which the small crystallites cover the entire sample with the aggregation regions[1]. The conclusion quantitatively showed that IL(q) is due to the correlations among the heterogeneous aggregation regions of the crystallites. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V55.00011: Effects of diffusion barriers on the temperature dependence of polymer crystallization rates Cai Jun, Jiping Wang, Wenbing Hu Jun Cai, Jiping Wang, Chenghuan Xu, Wenbing Hu* |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V55.00012: Low-Temperature Crystal Nucleation of Enantiomeric Poly (lactic acids) He Yucheng, Pengju Pan, Wenbing Hu We employed the commercial chip-calorimeter Flash DSC 1 to investigate the crystal nucleation behaviors of diblock copolymers and blends of half-half enantiomeric poly (lactic acids) at 35°C. The results show that crystal nucleation below the glass transition temperature can accelerates the crystallization rates at higher temperatures. For instance, the crystallization rate of 140°C increases by two orders of magnitude for the diblock copolymer. Such an accelerate can be attributed to the special interactions of stereo-complex crystals, because homo-crystal does not show such effect. |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V55.00013: Crystallization Behavior and Kinetics of Blends of PVDF with a Fluorinated Copolymer Nelaka Dilshan Govinna, Ilin Sadeghi, Ayse Asatekin, Christoph Schick, Peggy Cebe We present a study on crystallization of poly(vinylidene fluoride), PVDF, blended with a random fluorinated copolymer (FCP) of poly(methyl methacrylate) and 1H,1H,2H,2H-perfluorodecyl methacrylate. These blends are of interest as candidates for use as oil-water separation membranes. The glass transition and crystallization behavior were studied by fast scanning calorimetry using heating and cooling rates from 20 K/s to 4000 K/s. Crystal fraction and crystal formation rate decreased as the fraction of FCP increased in the blends. PVDF, which exhibits crystal polymorphism, crystallizes into β-phase when cooled from the melt at rates faster than 3000 K/s. Cooling rates between 2000 and 3000 K/s resulted in mixed α- and β-phase, while only α-phase occurred at rates slower than 2000 K/s. A series of isothermal melt crystallization experiments was carried out at temperatures in the range 80-120 °C for holding times of 0.1–100 s. It was found that β-phase crystal formation can be completely suppressed even at high cooling rates by generating a sufficient amount of α-phase crystals isothermally. The variation of these isothermal times and temperatures were also studied for the blends to study the effect of FCP in suppressing β-phase. |
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