Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A24: Semi-Crystalline and Structured Polymers |
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Sponsoring Units: DPOLY Chair: N. Sanjeeva Murthy, University of Vermont Room: Baltimore Convention Center 321 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A24.00001: Crystalline Structure, Morphology and Gas Transport in Semicrystalline Syndiotactic Polystyrene Brian Olson, Justin Brandt, Sergei Nazarenko Crystalline syndiotactic polystyrene (s-PS) continues to amuse the researchers by showing very unusual properties. This work mainly explored the remarkable free volume properties of the crystalline structure of this polymer, and also very unusual gas transport behavior. It was possible by varying the temperature of the melt and crystallization conditions to prepare a series of semicrystalline samples with different crystallinities (0-50\%) containing either pure $\alpha$-form, pure $\beta$-form and pure $\gamma$-form. Solid-state structure and the morphology of all prepared systems were examined by an assortment of techniques: DSC, density, WAXS, SAXS, and AFM. The structure was also probed by passing through small gas molecules, and by means of positron lifetime spectroscopy (PALS). [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A24.00002: Large Strain Requirements for Shear Induced Crystallization of Isotactic Polypropylene H. Henning Winter, Aadil Elmoumni, Deepak Arora Strain effects on the crystallization of a series of isotactic polypropylenes ($i$PP), with various molecular weights, were studied using rheology, light transmission, birefringence, differential scanning calorimetry, and wide-angle X-ray diffraction. Transmitted light intensity measurements demonstrate that the effect of pre-shear on crystallization rate keeps increasing up to very larger strain levels, much beyond strains that are required to reach steady shear flow (at given \textit{We}). Crystal orientation sets in at a total strain of about \textit{$\gamma $}$_{0}=$600 or higher. WAXD and DSC analyses corroborated the light transmission results. The samples were pre-sheared and then crystallized at constant temperature. Total shear strains \textit{$\gamma $}$_{0}$=200 to 1000 were applied to the $i$PP samples at the beginning of a crystallization experiment, after the samples had reached the crystallization temperature of 145$^{o}$C (under-cooled state). A constant Weissenberg number \textit{We}=1 (\textit{We}, defined as the product of shear rate and a relaxation time) was maintained throughout the study. \textit{We}=1 corresponds to the onset of shear thinning in steady shear. Deborah number values were low, \textit{De}$<<$1, indicating that steady shear flow had been reached in all pre-shearing runs. [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A24.00003: Real-time, Depth-Resolved Structure Development of Flow-Induced ``Skin-Core'' Morphologies in Polypropylene. Lucia Fernandez-Ballester, Derek Thurman, Igors Sics, Lixia Rong, Julie Kornfield We present a new method to isolate the signal arising from a given depth at each time point during flow-induced crystallization of isotactic polypropylene using real time rheo-optical and rheo-WAXD measurement based on the linear stress-depth relationship in a pressure-driven flow through a rectangular slit. Using thoughtfully selected sets of shearing conditions (constant ts with varied $\sigma $w), data analysis of the suite of experiments allows us to examine the incremental contribution to the real-time data from one shear stress to another (with all other conditions fixed) and to attribute the difference to a small spatial region of the sample. This ``depth sectioning'' technique has enabled us to confirm several existing results and uncovers several new keys to understanding how anisotropic crystalline is induced by flow. Threads first form near the channel wall where stress is highest and grow in length with prolonged flow. After sufficient time, thread length per unit volume saturates. The propagation of threads varies in a nonlinear manner with stress. Prior to saturation, thread propagation is linear with shearing time, providing promising conditions for measuring the thread propagation velocity. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A24.00004: Crystallization in Precision Polyolefins Rufina Alamo, Anindya Ghosal, Emine Boz, Kenneth Wagener, Riqiang Fu Understanding the crystallization behavior of highly branched polyolefins can be accomplished with model polymers with well defined microstructures. Models for branched polyethylenes with precisely placed O, F, Cl or Br on each and every 19 carbons have been synthesized via acyclic diene metathesis (ADMET) polymerization followed by hydrogenation. Compared to broad WAXS and DSC melting peaks of systems with a random distribution of the substituent, similar properties of precisely substituted polyolefins are very sharp, typical of the behavior of homopolymers. A uniform partitioning of the substituent between crystalline and non-crystalline regions, observed by NMR, relatively thick lamellar crystallites (240 A) and WAXS angular shifts, parallel the homopolymer-like crystallization behavior. In this series, orthorhombic isomorphic structures are maintained in O and F substituted polymers or up to a van der Waals radius of about 1.6 A, while accommodation of bulkier atoms in the lattice promotes the formation of a new triclinic form. A linear correlation between melting points and vdw radius in the halogen series is indicative to the degree to which each substitution perturbs the symmetry of the neighboring carbons in the lattice. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A24.00005: Transitions of Polymers with Precise Oligomethylene Sequences. Bernhard Wunderlich, Wulin Qiu Polyethylene, PE, with precise branches has been analyzed by TMDSC and X-ray diffraction. The branches were methyl, dimethyl, and ethyl groups. Furthermore, atactic poly(octadecyl acrylate) and poly(4,4'-phthaloimidobenzoyl-doeicosyleneoxycarbonyl) were studied. All are compared to LLDPE, of similar branch concentration and linear PE. Compared to LLDPE the precisely structured polymers show much sharper melting. Compared to HDPE lower melting temperatures and heats of fusion were observed, and all have non-orthorhombic structures. In contrast to paraffins of equal length which melt fully reversibly at a similar temperature, the precisely designed polymers melt largely irreversibly with only small amounts of reversing melting which is least for the best-grown crystals. These results have important implications for the description of melting of copolymers. Initial literature: W. Qiu, J. Sworen, M. Pyda, E. Nowak-Pyda, A. Habenschuss, K. B. Wagener, B. Wunderlich, \textit{Macromolecules}, \textbf{39} (2006). [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A24.00006: Ellipsometry as a Probe of Crystallisation Kinetics in Thin Diblock Copolymer Films Jessica L. Carvalho, Michael V. Massa, Kari Dalnoki-Veress We present our recent results on the use of ellipsometry to probe the crystallisation kinetics of thin films of a diblock-copolymer. Ellipsometry uses the ellipticity induced upon reflection of light from a film covered substrate to allow calculation of the refractive index and thickness of the film. By studying the temperature dependence of these quantities one can measure phase transitions including the crystallisation kinetics. The samples used are thin films of a polybutadiene-b-poly(ethylene oxide) diblock. The PB-b-PEO diblock has block molecular weight of 26,000 and 6,800 respectively and micro phase-separates into PEO minority spheres in a PB matrix. The study presented is very similar to what is typically performed by DSC, except that the ellipsometer also provides the expansion and contraction of the film (i.e. expansion coefficients, contraction upon crystallisation). We will discuss the results which can be obtained with this approach. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A24.00007: Growth mechanism changes in pseudo-dewetted monolayer poly(ethylene oxide) crystallization Dun-Shen Zhu, Er-Qiang Chen, An-Chang Shi, Stephen Cheng Crystal growth mechanism changes have been observed in pseudo-dewetted monolayers of low molecular weight (LMW) (PEO) on freshly cleaved hydrophilic mica surfaces [HPEO(4250) which have -OH groups at both ends and MHPEO(4700) which has one -OH and one -OCH$_{3}$ as end groups]. X-ray scattering reflectivity measurements show a wetted monolayer of molten PEO with a thickness of $\sim $ 4.5 nm on the mica surface. Non-adsorbed PEO droplets sit on top of the wetted monolayer. A two-step process for PEO single crystal growth under isothermal conditions was identified utilizing in-situ atomic force microscopy at different crystallization temperatures ($T_{x})$. In the first step, the crystal grows within the droplet which supplies the molten PEO that participates in the crystal formation. In this second-step, the wetted monolayer at the growth front is depleted by about 1.5 - 2.5 nm. The growing crystal lateral sizes obey a power law of $t^{\alpha }$ ($t$: time). At a high $T_{x}$ of 63 \r{ }C for MHPEO(4700), the growth behavior obeys \textit{r $\propto $ t} ($\alpha $ = 1). While in the case of HPEO(4250), its growth behavior follows \textit{r $\propto $ t}$^{0.5}$ ($\alpha $ = 0.5) in the whole $T_{x}$ range. With decreasing $T_{x}$, the growth of MHPEO(4700) falls into a scaling law of \textit{r $\propto $ t}$^{\alpha }$ (0.5 $< \quad \alpha \quad <$ 1). [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A24.00008: Guiding the orientation of polymer crystals by nano-imprint lithography Zhijun Hu, Jean-Fran\c{c}ois Gohy, Vincent Bayot, Alain Jonas Polymer crystallization is notoriously difficult to control at a local scale. Here, we report on a fast and easy method to guide the orientation of crystals of semicrystalline polymers at the nanometer scale by using nanoimprint lithography (1). Whenever a silicon mold bearing topographical nano-features (typical lateral size 50-250 nm; typical height 100 nm) is pressed against a molten film of a crystallizable polymer (poly(vinylidene fluoride was used here), the molten polymer is forced to flow into the cavities of the mold. The isolation of polymer in separate nano-cavities, which strongly decreases the importance of nucleation by impurities, the confinement of the polymer in nano-sized cavities, the probable partial orientation of chains near the vertical walls of the mold due to polymer flow, and interfacial effects, lead to a fine control over crystallographic orientation, crystal size and shape. This is shown for a series of geometries, from simple straight lines to more complex shapes such as concentric circles and small squares. References (1) Zhijun Hu et al., Nano Letters 2005, 5, 1738. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A24.00009: An Atomic Force Microscopy study of the thin film crystallization behavior of blends of poly-(L-lactide) and poly-(D-lactide). Yury Yuryev, Paula Wood-Adams, Josee Brisson, Marie-Claude Heuzey, Charles Dubois Blends of poly-(L-lactide) and poly-(D-lactide) form a triclinic stereocomplex during racemic crystallization while the pure optical isomers crystallize in a pseudo-orthorhombic crystalline form. The triclinic stereocomplex has a high melting point of 503 K compared to 453 K for the other crystalline form. Atomic Force Microscopy (AFM) allows one to image a polymer surface with nanoscale resolution and is best suited for the studies of crystalline morphology in thin polymer films. Individual spherulitic morphology, its growth rate and its dependence on temperature and blend composition were studied using tapping mode AFM. 500-600 nm thick polylactide films were produced by solution casting. Excess nucleation sites were eliminated by melting for a short time. It is found that spherulites protrude from the surface of the film after annealing. The crystallization rate is slower when both optical isomers are present. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A24.00010: Spectroscopic Analysis of Unusual Poly (lactic acid) Structures. Kaoru Aou, Guolin Wu, Shuhui Kang, Shaw Ling Hsu Poly (lactic acid) (PLA) is a biomass-derived polymer with a broad range of applications. We previously unambiguously determined the chain conformation of PLA to be a 10/3 helix based on a combination of experimental and normal coordinate analyses, in the process assigning band splittings to the intrahelical interactions. Here, we investigate the nature of intermolecular interactions within the PLA crystals as well as their molecular orientation. In PLA, specific intermolecular interactions such as dipolar coupling strongly influence the spectral features. Crystal field splitting bands in the PLA crystal vibrational spectra were identified. They indicated the strength and proximity of interacting carbonyls and C-H groups and are thus relevant to PLA crystal packing. Results of the studies were used to understand the origins of unusual thermal stability of the PLA stereocomplex with a melting point higher than the $\alpha $-crystal by at least 50 $^{o}$C. The knowledge was also applied to characterization of orientation development in PLA tubes during different stages of sequential biaxial deformation. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A24.00011: Poly(L-lactic acid) Crystals: From 2D to 3D Suolong Ni, Robert E. Major, Alan R. Esker The crystallization behavior of poly(L-lactic acid) (PLLA) is studied in Langmuir and Langmuir-Blodgett (LB) films. PLLA Langmuir films exhibit a first-order liquid expanded to condensed (LE/LC) phase transition. Temperature dependent isotherm studies reveal an experimentally accessible critical temperature (Tc) for the LE/LC phase transition. Below Tc, the LE/LC phase transition induces the ordering of PLLA single chain helices, giving rise to two dimensional (2D) smectic liquid crystalline-like lamella in the condensed phase. The nucleation and growth of three dimensional (3D) crystals from 2D helices can be achieved through isobaric experiments. Above Tc, PLLA Lamgmuir monolayers collapse directly from the isotropic LE phase to form 3D single crystals. Annealing studies of the LB-films with 2D lamellar patterns via in-situ atomic force microscopy track the time and temperature dependence growth of 3D crystals. Our system provides a model system for studying crystallization kinetics in ultra-thin films. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A24.00012: Amylose Crystallization From Concentrated Aqueous Solution: Role of Degree of Polymerization John Creek, James Runt, Gregory Ziegler In earlier research, we demonstrated that amylose forms a spherulitic morphology when crystallized from concentrated amylose - water solutions, over a wide degree of crystallization conditions. The process has been described as depending on a competition between crystallization and liquid-liquid phase separation processes. In the present study acid degradation and enzymatic debranching are utilized to create a number of amylose fractions differing in degree of polymerization, ranging from DPs of 20 to 920. It was determined (using DSC and x-ray diffraction) that the shorter the chain length, the higher the final degree of crystallinity. Atomic force microscopy is used to investigate the microstructure of amylose lamella within the spherulites. [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A24.00013: Diffusion-limited growth of poly (caprolactone) in poly (tert-butyl acrylate) matrices at the air/water interface Bingbing Li, Alan R. Esker Surface pressure induced crystallization of poly (caprolactone) (PCL) in poly (tert-butyl acrylate) (PtBA) matrices at the air/water interface has been monitored in real time by Brewster angle microscopy (BAM). Diffusion-limited morphologies of PCL crystals grown in PCL/PtBA mixed monolayers were observed during the compression process. The lateral forces applied on the mixed monolayer during compression assist the diffusion of PCL molecules from the surrounding monolayer to the crystal growth fronts, where the amorphous PtBA components are excluded. Surface pressure-area per monomer isotherm studies suggest that the nucleation and growth of PCL occurs at about 11 mN/m. The lamellar thickness of PCL dendrites determined by atomic force microscopy is about 7-8 nm. With decreasing surface concentration during expansion of the mixed films, PCL chains slowly detach from the crystalline domains and diffuse into the monolayer. These findings provide an interesting model system for future studies of crystallization in confined geometries. [Preview Abstract] |
Monday, March 13, 2006 10:36AM - 10:48AM |
A24.00014: Crystallization and orientation studies in SWNTs based nanocomposites Tirtha Chatterjee, Ramanan Krishnamoorti, Viktor Hadjiev Single walled carbon nanotubes (SWNTs) based polymer nanocomposites are attractive for their improved mechanical, electrical and thermal properties. We have obtained well-dispersed SWNTs samples in two semi-crystalline polymers poly($\varepsilon $-caprolactone) and poly(ethylene oxide) respectively. Initial crystallization studies show tubes acts as a nucleating agent for PCL where as it hinders nucleation of PEO crystals. Both polymer composites are studied for aligned SWNTs samples. Raman spectroscopy studies show SWNTs are aligned along the draw direction. The crystallization studies of the aligned nanocomposites are performed using synchrotron small angle x-ray scattering (SAXS). Our studies reveal that for an aligned tube direction polymer crystals arrange themselves in a particular orientation. For PCL the lamellar normal is parallel to the tube axis where as for PEO it is perpendicular to the draw direction. As SWNTs act as a nucleating agent for PCL, chains grow parallel to the draw direction. For PEO, SWNTs act as barriers and polymer lamellae grow parallel to the SWNTs axis. This observation is interesting because oriented tubes can be used as a template to orient polymer crystals. [Preview Abstract] |
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