Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y20: Semi Crystalline Polymers |
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Sponsoring Units: DPOLY Chair: Kari Dalnoki-Veress, McMaster University Room: 405 |
Friday, March 7, 2014 8:00AM - 8:12AM |
Y20.00001: Nanoscale alignment of interfacial crystallites and effects on electrical properties on oCVD PEDOT polymer Asli Ugur, Ferhat Katmis, Kripa K. Varanasi, Karen K. Gleason The precise mechanism of charge transport in conducting polymers is not yet fully understood. It can be influenced by multiple factors including, long- and short-range ordering of the polymeric chains, degree of crystallinity, crystallite size, morphology, and defects. Here we demonstrate that the chain orientation of poly (3,4-ethylenedioxythiophene) (PEDOT) can be controlled by oxidative chemical vapor deposition (oCVD) and the controlled orientation is used to understand the efficient transport direction to obtain high electrical conductivity. The parallel polymer backbone to the substrate resulted in higher conductivities compared to the chains that are perpendicularly oriented with respect to the substrate, where the conductivity is measured both in in-plane and out of plane directions. As film thickness decreases, the electrical conductivity reveals a remarkable improvement, up to $\sim$3000 S/cm by using high substrate deposition temperatures. We have correlated the electrical properties with structural features, e.g. the interface, density and domain sizes of the polymer films by using X-ray and electron based diffraction measurements. [Preview Abstract] |
Friday, March 7, 2014 8:12AM - 8:24AM |
Y20.00002: Manipulation of P3AT Crystallization Behavior Bryan S. Beckingham, Victor Ho, Rachel A. Segalman While the commonly studied P3HT has a final melting transition approaching that of its thermal degradation; by judicious substitution of the alkyl side chain the melting transition can be controlled over a range of approximately 150C. Specifically, P3EHT has a melting transition that occurs between 35 and 85C, well below potential degradation temperatures, making P3EHT a model system for examining crystallization in P3ATs. Interestingly, the observed melting endotherms of P3ATs are multimodal in nature such that upon isothermal crystallization of P3EHT, three distinct peaks are observed by differential scanning calorimetry upon heating. Here, we resolve the lowest temperature feature to be a result of a rigid amorphous fraction forming at long times and high relative crystallinity. Moreover, we demonstrate that the two more distinct higher temperature features are a consequence of a melt-recrystallization process. Lastly, we explore how by understanding these processes the initial crystallization conditions and subsequent thermal treatments can be used to manipulate the crystal populations and thereby the properties of P3EHT. [Preview Abstract] |
Friday, March 7, 2014 8:24AM - 8:36AM |
Y20.00003: Fabrication of a Conjugated Polymer on Surfaces Studied by Electron Microscopy Hiroshi Jinnai, Takeshi HIguchi, Daiki Murakami, Mitsuo Suga, Atsushi Takahara A controlled ``in-situ'' nano-patterning is highly demanded in various fields of nano-technology. A nano-rod array oriented perpendicular to the substrate is one of the typical nano-structures useful in energy, biomimetic and memory applications. We here proposed a novel nano-patterning method to synthesize polymers by irradiation of electron beam into monomer liquid under atmospheric pressure and concurrently to pattern nano-rod array by scanning the beam. A polymer that can be synthesized by this method includes the poly(3-hexylthiophene), one of the most frequently used conjugated polymers in an organic photovoltaic device. The ``Atmospheric Scanning Electron Microscope (ASEM),'' which enables us to observe morphologies and dynamic phenomena in liquid under atmospheric pressure, was used for fabricating nano-rod structures in this study. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 8:48AM |
Y20.00004: Formation and Characterization of Lyotropic Liquid Crystal Phase in Poly(3-hexylthiophene) Solutions Nabil Kleinhenz, Karthik Nayani, Sourav Chatterjee, Xujun Zhang, Jung Ok Park, Mohan Srinivasarao, Paul Russo, Elsa Reichmanis We have studied poly(3-hexylthiophene) (P3HT) as a model~$\pi $-conjugated polymer for organic semiconductor applications and have investigated the formation of a lyotropic liquid crystalline phase that might be a potential precursory to well-ordered thins film for device applications. Through various processing techniques including the use of mixed solvent systems, slow solution cooling, aging, and capillary flow, we have observed persistent birefringence and alignment of P3HT~in solution. Raman spectroscopy of these solutions in capillaries displays anisotropy in their Raman spectra. UV-Vis spectroscopy was employed to understand the intermolecular interactions that give rise to alignment, and dynamic light scattering was used to quantify the dimensions of P3HT aggregates.~ [Preview Abstract] |
Friday, March 7, 2014 8:48AM - 9:00AM |
Y20.00005: Controlling the Thermal and Optoelectronic Properties in Poly(3-alkylthiophene) Random Copolymers Victor Ho, Hoi Ng, Rachel Segalman Although thermal annealing is a common technique for changing the crystalline texture of polymer-based active layers, the high thermal transition temperatures of many conjugated polymers, such as poly(3-alkylthiophenes) (P3ATs), prevents precise control over the morphology and optoelectronic properties studied at room temperature. In the past we have shown that substitution of the aliphatic side chain is an effective method to alter thermal transitions over a range of 150C while still retaining similar crystalline texture in homopolymer thin films. In this talk random copolymerization of P3ATs results in cocrystallization of repeat units over all the entire range of compositions into unit cells which are related to one of the two parent homopolymers. In turn, the optical absorption edge closely matches that of either of the two homopolymers while the melting temperatures gradually transition between that of the pure components. This presents a synthetically convenient approach to controlling the melting transition of conjugated polymers without detrimentally affecting the optical absorption. [Preview Abstract] |
Friday, March 7, 2014 9:00AM - 9:12AM |
Y20.00006: Quantifying Order in Poly(3-hexylthiophene) Chad Snyder, Ryan Nieuwendaal, Dean DeLongchamp, Christine Luscombe, Prakash Sista, Shane Boyd While poly(3-hexylthiophene) (P3HT) is one of the most studied polymers in organic electronics, it remains one of the most challenging in terms of quantitative measures of its order, e.g., crystallinity. To address this challenge, we prepared a series of highly regioregular P3HT fractions ranging from 3.3 kg/mol to 23 kg/mol. Using this series plus a high molar mass (62 kg/mol) commercial material, we compare different metrics for order in P3HT via calorimetry, solid state NMR, and x-ray diffraction. We reconcile the results of our work with those of recent studies on oligomeric (3-hexylthiophenes). One challenges of quantifying low molar mass P3HT samples via DSC is a thermal fractionation effect due to varying chain lengths. We quantify these effects in our molar mass series, and a clear crossover region from extended chain crystals to chain folded crystals is identified through the thermal fractionation process. New values for the enthalpy of fusion of high molar mass P3HT and its equilibrium melting temperature are established through our work. Another result of our research is the validation of high heating rate DSC methods for quantifying crystallinity in P3HT samples with device relevant film thicknesses. [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:24AM |
Y20.00007: Counit Inclusion in Hydrogenated Polynorbornene Copolymer Crystals Adam Burns, Michael Showak, Andrew Stella, Richard Register Crystallization in poly(A-\textit{co}-B) random copolymers, where homopolymer A is crystalline but B is not, is dictated by the degree to which crystals of A can include B units. Typically, B units are strongly excluded from the A crystals, drastically reducing the degree of crystallinity w$_{c}$ and crystal thickness t$_{c}$ even at modest comonomer contents. However, in some cases, B units can be incorporated into the crystals as defects, significantly diminishing the counits' impact on w$_{c}$ and t$_{c}$. The extent and consequences of counit inclusion have been investigated in hydrogenated polynorbornene (hPN) with alkylnorbornene counits, synthesized by living ring-opening metathesis polymerization followed by hydrogenation. In the case of 5-hexylnorbornene (HxN) counits, a steep decline in w$_{c}$ and t$_{c}$ with counit content is found, indicative of strong exclusion. In contrast, when the counits are 5-methylnorbornene (MeN), extensive inclusion of MeN units into the crystals is observed. hP(N-\textit{co}-MeN) copolymers maintain appreciable crystallinity above 30 mol{\%} MeN, and the dependence of the melting point T$_{m}$ on t$_{c}$ tracks that of the hPN homopolymer. Four times as much MeN as HxN (molar basis) is required to produce a comparable drop in w$_{c}$. Therefore, copolymerization with MeN can be used to tune T$_{m}$ without drastically reducing w$_{c}$. Additionally, hPN exhibits a polymorphic transition to a rotationally disordered (RD) crystal at temperature T$_{cc\, }$\textless T$_{m}$. Incorporation of comonomers increases the disparity between T$_{m}$ and T$_{cc}$, indicating that thin crystals stabilize the RD phase. [Preview Abstract] |
Friday, March 7, 2014 9:24AM - 9:36AM |
Y20.00008: Curvature-directed crystallization of polymer dielectrics in nanopores Dariya Reid, Bridget Ehlinger, Lin Shao, Jodie Lutkenhaus When a polymer is constricted in geometries smaller than its unperturbed molecular size its properties may greatly differ from the bulk state. The effect of cylindrical confinement on crystallization of isotactic polypropylene (iPP) and polycarbonate (PC) was studied. Polymer nanowires were prepared by melt-wetting into nanoporous templates of varying diameter (15 -- 200 nm). X-ray diffraction (XRD) studies reveal that iPP crystallizes into the $\alpha $-phase and preferentially orients along the long axis of the pore. Using differential scanning calorimetry (DSC) it is shown that iPP transitions from hetero to homogeneous nucleation as the pore diameter decreases. The isothermal crystallization kinetics is analyzed using Avrami analysis and a progression, with time, into primarily 1D crystallization is presented. [Preview Abstract] |
Friday, March 7, 2014 9:36AM - 9:48AM |
Y20.00009: SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in shear flow Binbin Luo, Wesley Burghardt Flow-induced crystallization of poly(1-butene) was studied in shear flow, produced using a Linkam shear cell modified to allow x-ray access for in situ synchrotron x-ray scattering measurements. After loading in the the shear cell, samples were first heated well into the melt, and then cooled to a crystallization temperature selected such that negligible quiescent crystallization would occur on reasonable time scales. A short burst of shear flow was then applied at various rates, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) data were collected to study the resulting accelerated crystallization kinetics, as well as the morphology of the resulting crystallites (e.g. degree of crystallite orientation). SAXS and WAXS data provided generally self-consistent measures of the extent of crystallization, although WAXS data consistently reported a higher degree of crystallite orientation than SAXS. Average crystallite orientation was found to decrease over the course of crystallization. The impact of both deformation rate and total applied strain on the crystallization process were examined. The sample was also studied under similar flow conditions using (i) turbidity and (ii) linear viscoelasticity as probes of the developing crystallinity. [Preview Abstract] |
Friday, March 7, 2014 9:48AM - 10:00AM |
Y20.00010: Extensional Flow Induced Crystallization of Polyethylene David Nicholson, C. Rebecca Locker, Andy Tsou, Gregory Rutledge The majority of manufactured polyethylene is used in films mostly through the blown film fabrication process where extensional flow induced crystallization is a critical component in affecting the development of crystalline morphology and amorphous topology. In order to optimize the blown film performance, it is critical to understand the mechanism of extensional flow induced crystallization of polyethylene. Model high density polyethylene with a $M_n$ of 20,000 g/mol and a PDI (polydispersity) of 2 and lower were synthesized by organometallic catalysts. Extensional flow induced crystallization of these materials was measured using the SER (Sentmanat Extensional Rheometer) either at a given rate with varying temperatures or vice versa. A continuum model was applied to analyze the flow induced crystallization data. All samples after extensional flow were quenched in ice water and the resulting morphology was characterized using SAXS and WAXS. The extensional rate was found to be effective in modifying morphology whereas the temperature was not; neither temperature nor strain rate affected the final film crystallinity. With an increase in extensional rate, crystallites became thinner and narrower with potentially higher connectivity which could lead to higher toughness. [Preview Abstract] |
Friday, March 7, 2014 10:00AM - 10:12AM |
Y20.00011: SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow Erica McCready, Wesley Burghardt We report studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow. Flow was produced using an SER extensional flow fixture housed in a custom built convection oven designed to provide x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. Samples were loaded into the SER fixture, heated well into the melt, and then cooled to a temperature at which quiescent crystallization would be prohibitively slow. A short interval of uniaxial extensional flow was then applied, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) patterns were collected to study the phase transformation kinetics and morphology of the subsequent accelerated crystallization. The degree of crystallite orientation was generally found to decrease over the course of the crystallization. WAXS measurements yielded systematically higher degrees of crystallite orientation than SAXS. Both SAXS and WAXS gave generally consistent results for the extent of crystallization, although the SAXS invariant showed a decrease at long times that is not mirrored in the WAXS data. The impact of both deformation rate and total applied strain on the crystallization process were examined. [Preview Abstract] |
Friday, March 7, 2014 10:12AM - 10:24AM |
Y20.00012: Probing the interlamellar amorphous phase in semicrystalline polyolefins using vapor flow and neutron scattering Amanda McDermott, Chad Snyder, Ronald Jones Measuring equilibrium swelling as a function of solvent vapor activity is an established method of simultaneously measuring the polymer-solvent interaction parameter and the properties of crosslinks---or in semicrystalline polymers, tie-chains, which strongly impact mechanical properties. Gravimetric experiments do not differentiate between uptake by extralamellar and interlamellar amorphous material and determine amorphous layer swelling by treating the permeant and amorphous phase as incompressible fluids. Measurements of swelling and solvent uptake that are \textit{independent} of one another and \textit{specific} to interlamellar amorphous material could enhance understanding of mechanical properties, barrier properties, and solvent processing. Small-angle neutron scattering combined with \textit{in situ} swelling by deuterated solvent vapor fulfills this requirement. A shift in the long-period peak wavevector indicates swelling, while peak intensity independently indicates interlamellar solvent concentration. Preliminary results suggest that interlamellar polymer-solvent energetic interactions may be affected by mesophases with chain orientation and mobility different from the bulk. [Preview Abstract] |
Friday, March 7, 2014 10:24AM - 10:36AM |
Y20.00013: An Integrated Ultrafast Scanning Calorimetric and Micro Raman Spectroscopic Investigation of Polymer Crystallization Dongshan Zhou, Lai Wei, Jing Jiang, Gi Xue, Xiaoliang Wang Ultrafast differential scanning calorimetry (UFDSC) with scanning rate up to 1,000,000 K/s has already been used to study the kinetics of crystallization and phase transition of some polymers and liquid crystal. Recently, we developed stage type UFDSC (ST-UFDSC) with comparable controlled heating and cooling rates. ST-UFDSC enables sample treatment and measurement integrated with microstructural characterization. As an example, we investigated the Raman spectroscopy of PET at different crystallization stage obtained by programed rapid cooling and heating processes. Although the Raman spectroscopy is not acquired during rapid heat treatments, the structure is assumed to remain by ultrafast quench below the glass transition temperature, when the Raman spectroscopy is collected. We expect that the combination technique can be also used to investigate dynamic relaxation behaviors of metastable states obtained by ultrafast heat treatments. [Preview Abstract] |
Friday, March 7, 2014 10:36AM - 10:48AM |
Y20.00014: Molecular mechanism of viscoelasticity in aligned polyethylene Ali Hammad, Hikmatyar Hasan, Thomas Swinburne, Stefano Del Rosso, Lorenzo Iannucci, Adrian Sutton Aligned polyethylene is used in industrial and medical applications due to its low density and high tensile strength. Extensive experimental work has been done to determine its mechanical properties, notably its viscoelasticity. However, the molecular processes that underlie these macroscopic properties are poorly understood. We develop a united atom model of aligned chains, in which intermolecular interactions are modelled by a Lennard-Jones potential, and the elastic energy within chains is modelled with harmonic springs. Using this simple model, we demonstrate the nucleation of solitons from chain ends, as one molecular chain is stretched with respect to another, and how load is transferred between chains in disregistry by intermolecular interactions. We develop an equation of motion for the movement of solitons along molecular chains, allowing us to replace a collection of aligned chains with a gas of solitons. Although solitons have been invoked to account for dielectric relaxation in crystalline regions of polyethylene, we believe this may be the first time they are discussed in the context of mechanical properties of aligned polyethylene. [Preview Abstract] |
Friday, March 7, 2014 10:48AM - 11:00AM |
Y20.00015: Holographic reconstruction from electron diffraction patterns: true atom images of thousands of atoms Carsten Westphal, Tobias Luehr After its discovery in the early 70ies of the last century x-ray photo-electron diffraction (XPD) has been very successfully applied for the characterization of crystalline systems and adsorbate structures later. The emitted electron wave contains the full spatial information of the atoms' arrangement around the emitter atom. However, a holographic reconstruction yielding a 3-dimensional image of the investigated structure was with the exception of a very few special cases rarely successful. In most cases, the reconstruction contained strong image distortions due to the strong anisotropic scattering characteristics in the electron-atom interaction. Here, we present a new approach from angle-resolved diffraction patterns recorded at electron kinetic energies above 10 keV for the first time. The new reconstruction scheme is a direct method for revealing the crystal structure without any further information. We present spatial images of different crystal systems showing thousands of atoms at their correct location. [Preview Abstract] |
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