Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R6: Polymer Melts and Solutions |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Guruswamy Kumaraswamy, CSIR-NCL Room: 265 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R6.00001: Flexibility governs diffusivity of active colloidal chains Bipul Biswas, Guruswamy Kumaraswamy, Raj Manna, Abhrajit Laskar, Sunil Kumar, Ronojoy Adhikari We use ice templating to form “polymeric” chains of colloidal particles. Here, the colloidal particles are bonded together through a flexible crosslinked polymer mesh. Adjusting the crosslink density in this mesh allows us to tune the flexibility of the colloidal chains. The advantage of this model is that the spatial coordinate of each monomer along these chains can be tracked using optical microscopy. We present data on colloidal chains that have been rendered “active” by coating the colloidal chains with platinum nanoparticles that catalyze the decomposition of hydrogen peroxide. We measure the center of mass diffusion of colloidal chains as a function of chain length and contrast active and Brownian chains. The diffusivity of Brownian chains decreases as chain length increases, and is not strongly dependent on the chain flexibility. In contrast, the diffusivity of active chains increases with increase in chain flexibility. Our experiments accord well with models that ascribe the activity as arising from hydrodynamic interactions from stresslets distributed along the chain length. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R6.00002: Many-Body Dissipative Particle Dynamics Simulations of Polymer Solutions: Hydrodynamic Interactions and Entanglements Xin Yong Using many-body dissipative particle dynamics (MDPD), I model polymer solutions with concentrations spanning dilute and semidilute regimes and examine static and dynamic properties of polymer chains, focusing on hydrodynamic interactions and entanglements. The parameterization of MDPD interactions for solvated polymer chains in a liquid-vapor coexistent state is first established by mapping to the mean-field Flory-Huggins theory. The coil-globule transition of polymer chains in dilute solutions is characterized by varying solvent quality and measuring the radius of gyration and end-to-end distance. Both static and dynamic scaling relations for polymer chains in poor, theta, and good solvents are in good agreement with the Zimm theory in which the hydrodynamic interactions are considered. Semidilute solutions with polymer volume fractions up to 0.7 exhibit the screening of excluded volume interactions due to chain overlapping and subsequent shrinking of coils in the good solvent. Furthermore, entanglements become dominant in the semidilute solutions, which inhibit diffusion and relaxation of chains. Quantitative analysis of topology violation confirms that entanglements are correctly captured in the MDPD simulations. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R6.00003: Preventing Small Molecule Nucleation and Crystallization by Sequestering in a Micelle Corona Ziang Li, Lindsay Johnson, Ralm Ricarte, Letitia Yao, Marc Hillmyer, Frank Bates, Timothy Lodge We exploited a blend of hydroxypropyl methylcellulose acetate succinate and poly(N-isopropylacrylamide) (PNIPAm) to improve the solubility and dissolution of a rapidly crystallizing model drug molecule phenytoin and observed synergistic effect in vitro at constant drug loading by varying the blending ratio. Dynamic and static light scattering experiments showed that PNIPAm self-assembled into micelles in aqueous solution. We believe that adding these PNIPAm micelles inhibited both nucleation and crystal growth of phenytoin based on the polarized light micrographs taken from the dissolution media. The drug-polymer intermolecular interaction was revealed by nuclear Overhauser effect spectroscopy and further quantified by diffusion ordered spectroscopy. We found that the phenytoin molecules were sequestered in aqueous solution by partitioning into the corona of the micelle. The blend strategy through the use of self-assembled micelles showcased in this study offers a new platform for designing advanced excipients for oral drug delivery. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R6.00004: Viscoelastic Relaxation of Mono-functionally End-Associating Rouse Chains: Experimental Test Hiroshi Watanabe, Yumi Matsumiya Viscoelastic test was made for end-calboxylated polyisoprene (PI-COOH) of the molecular weight M $=$ 30.5k that underwent the inter-chain association and dissociation through hydrogen bonding of the COOH groups at the chain end. As a reference, the test was made also for neat PI unimer and PI2 dimer (both having no COOH group at the chain end). These samples were diluted in oligomeric butadiene (oB) to a concentration of 10 wt{\%}. The neat unimer and dimer exhibited non-entangled Rouse behavior at this concentration, as expected from their molecular weights. At low temperatures (T $\le $ 0 C), the PI-COOH sample relaxed slower than the reference unimer but faster than the dimer, whereas the relaxation of PI-COOH approached that of the unimer with increasing T \textgreater 0 C, and this change of the relaxation time of PI-COOH was associated with changes in the relaxation mode distribution. This behavior of PI-COOH was well described by a recently proposed theory considering motional coupling between the end-associating unimer and its dimer at chemical equilibrium. On the basis of this result, an effect of the polymeric character of PI-COOH chain on the viscoelastically detected association/dissociation of the COOH groups is discussed. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R6.00005: Melt extending polyisoprene to develop new understanding of nonlinear polymer rheology Jianning Liu, Yi Feng, Misichronis Kostas, Apostolos Avgeropoulos, Shi-Qing Wang This study investigates all aspects of nonlinear rheological responses of linear polyisoprene melts in uniaxial extension. On one hand, we demonstrate a) the failure of the conventional theory to explain the difference in the responses to startup extension between entangled melts and entangled solutions (made of high and low molecular weights) and b) the need to treat entangled polymers as an explicit network. On the other hand, we investigate whether and how the transition from yielding and extensional softening to true strain hardening and melt rupture takes place in weakly entangled polyisoprene and whether a breakdown of time-temperature superposition occurs, as it did in styrene butadiene rubbers. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R6.00006: Fingerprinting molecular deformation of entangled polymers by small-angle neutron scattering Yangyang Wang, Zhe Wang, Christopher Lam, Weiyu Wang, Jianning Liu, Yun Liu, Kunlun Hong, Christopher Stanley, Wei-Ren Chen During the last several decades, the study of the dynamics of entangled polymers has been focusing on the application of the tube model. Despite the tremendous success of this theoretical approach, a key hypothesis of the tube model concerning nonlinear viscoelasticity has not been fully validated by experiments. In this work, we critically examine the molecular deformation of entangled polymers by small-angle neutron scattering (SANS) experiments. A new approach, based on spherical harmonic expansion analysis, has been developed to decompose the 2D anisotropic scattering pattern. This development makes it possible to unambiguously examine the deformation mechanism predicted by statistical and molecular models of entangled polymers at the microscopic level. Our SANS measurements on uniaxially stretched polystyrene melts show that the tube model could not describe the \textit{Q}-dependent spherical harmonic expansion coefficients determined from experiments, as it significantly overestimates the deformation anisotropy. The failure of the model stems from its assumption of \textit{chain retraction within an affinely-deformed tube}. New insights for understanding the nonlinear flow behavior of entangled polymers will be discussed in this talk. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R6.00007: How mechanical behavior of glassy polymers enables us to characterize melt deformation: elastic yielding in glassy state after melt stretching? Shi-Qing Wang, Zhichen Zhao, Mesfin Tsige, Yexin Zheng Fast melt deformation well above the glass transition temperature Tg is known to produce elastic stress in an entangled polymer due to the chain entropy loss at the length scale of the network mesh size. Here chains of high molecular weight are assumed to form an entanglement network so that such a polymer behaves transiently like vulcanized rubber capable of affine deformation. We consider quenching a melt-deformed glassy polymer to well below Tg to preserve the elastic stress. Upon heating such a sample to Tg, the sample can return to the shape it took before melt deformation. This is the basic principle behind the design of all polymer-based shape-memory materials. This work presents intriguing evidence based on both experiment and computer simulation that the chain network, deformed well above Tg, can drive the glassy polymer to undergo elastic yielding. Our experimental systems include polystyrene, poly(methyl methacrylate) and polycarbonate; the molecular dynamics simulation is based on Kremer-Grest bead-spring model. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R6.00008: How does a polymer swell in poor solvent mixtures? Debashish Mukherji, Carlos Marques, Torsten Stuehn, Kurt Kremer Macromolecular solubility in solvent mixtures often strike as a paradoxical phenomena. In a system where all particle interactions are repulsive, chains can nevertheless collapse, due to increased repulsive monomer-solvent interactions that lead to an effective attraction between monomer units also known as depletion induced attraction. While it is well understood why a polymer can collapse in a purely repulsive solvent, polymer swelling at intermediate mixing ratios of two repulsive solvents still lacks a microscopic explanation. Here, for binary solvent mixtures, we combine computer simulations and theoretical arguments to unveil the microscopic, generic origin of this collapse-swelling-collapse scenario. We show that this phenomenon naturally emerges at constant pressure in mixtures of purely repulsive components when a delicate balance of the entropically driven depletion interactions is achieved. [1] D. Mukherji, C. M. Marques, T. Stuehn, and K. Kremer, arXiv:1609.09839 (2016). [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R6.00009: Dynamics of Entangled Polymers: Role of Attractive Interactions Gary S. Grest, Jason Koski The coupled dynamics of entangled polymers, which span broad time and length scales, govern their unique viscoelastic properties. Numerical simulations of highly coarse grained models are often used to follow chain mobility from the intermediate Rouse and reptation regimes to the late time diffusive regime. In these models, purely repulsive interactions between monomers are typically used because it is less computationally expensive than including attractive interactions. The effect of including the attractive interaction on the local and macroscopic properties of entangled polymer melts is explored over a wide temperature range using large scale molecular dynamics simulations. Attractive interactions are shown to have little effect on the local packing for all temperatures T and chain mobility for T higher than about twice the glass transition T$_g$. For lower T, the attractive interactions play a significant role, reducing the chain mobility compared to the repulsive case. As T approaches T$_g$ breakdown of time-temperature superposition for the stress autocorrelation function is observed. Sandia National Labs is a multiprogram laboratory managed and operated by Sandia Corporation, a Lockheed-Martin Company, for the U.S. Dept of Energy under Contract No. DEAC04-94AL85000. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R6.00010: Crossover Behavior of Gas Transport in Polymer Melts: A Molecular Simulation Approach to the Robeson Plot Kai Zhang, Sanat Kumar Efficient and selective transport of small gas molecules using lightweight and easily processable polymeric membranes is crucial in many clean energy technologies. For a pair of wanted (A) and unwanted (B) gases, the performance of membrane separation is characterized by the permeability of A (P$_{\mathrm{A}})$ and the selectivity of A with respect to B ($\alpha _{\mathrm{AB}}=$P$_{\mathrm{A}}$/P$_{\mathrm{B}})$. Empirically, the so-called Robeson plot, i.e. the scatter plot of $\alpha_{\mathrm{AB}}$ versus P$_{\mathrm{A}}$, exhibits a tradeoff relation, whose upper bound sets the optimal membrane separation limit. Simple thermodynamic and kinetic argument like the Freeman theory predicts that the slope magnitude ($\lambda )$ of the upper bound is purely determined by the molecular size ratio as $\lambda =$(d$_{\mathrm{B}}$/d$_{\mathrm{A}})^{\mathrm{2}}$-1. However, systematic studies of the Robeson plot on the molecular level and a quantitative understanding of the microscopic mechanisms that control the separation ability are still missing. We perform molecular dynamics simulation to calculate the permeability of model gas molecules in coarse-grained polymer melts, from which the corresponding Robeson plot is constructed. We observe a crossover behavior of gas transport as the gas size is tuned from below to above approximately twice the monomer size. The Freeman prediction is only valid in the large gas size limit. Further investigations on the gas dynamics show that its diffusion behavior changes from a geometric obstruction mechanism to an activated trap-and-jump process. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R6.00011: Polymer Dynamics Studied by Field-Cycling NMR Relaxometry Marius Hofmann, Benjamin Kresse, Alexei Privalov, Franz Fujara, Nail Fatkullin, Ernst Roessler We apply Field-Cycling (FC) $^{1}$H NMR relaxometry to study translational as well as reorientational segmental dynamics in linear polymer melts. Assuming frequency-temperature superposition the fluctuation spectrum of the dipole-dipole interaction J($\omega )$ is probed over ten decades in frequency, covering the local, Rouse and entanglement dynamics at high M. Fourier transformation yields the dipolar correlation function C$_{DD}$(t), which turns out to be generic for different polymers with comparable M. Using the isotope dilution technique C$_{DD}$(t)$=$C$_{intra}$(t)$+$C$_{inter}$(t) is separated into an intra- and an intermolecular component. While C$_{intra}$(t)$=$C$_{2}$(t) reflects reorientational motion in terms of the l$=$2 Legendre polynomial, C$_{inter}$(t) is related to translation, specifically to the segmental mean square displacement. The found transition from Rouse to constrained Rouse dynamics is probed, and the data agrees with such of neutron scattering well. Combining FC and field-gradient NMR all four power-law regimes of the tube-reptation (TR) model are reproduced. Concerning reorientation, however, C$_{2}$(t) doesn't conform to the TR model, a result which is also verified by FC $^{2}$H relaxometry. Based on our findings the return-to-origin hypothesis is challenged. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R6.00012: Multipoint Segmental Repulsive Potential Model for Dissipative Particles Dynamics of Uncrossing Polymer Chains Nobuyuki IWAOKA, Katsumi HAGITA, Hiroshi TAKANO In scientific and industrial fields, dissipative particle dynamics (DPD) simulation is a widely used coarse-grained molecular dynamics for studying the structural and thermodynamic properties of polymeric systems. A long-standing problem in DPD polymers is that unphysical bond crossings are caused due to utilization of soft-core potential. This means that the standard DPD cannot capture entanglement effects that play a crucial role in mechanical properties of long polymers. To overcome such a drawback, a segmental repulsive potential (SRP) model has been developed by several groups. In the SRP models, repulsive potential between bonds is added to the DPD polymer as a function of the distance between nearest points or midpoints on each bond. The SRP models have been shown that bond crossings are effectively reduced and reptation-like behaviors are successfully reproduced. However, cut-off radius of the SRP $d_{\rm c}$ (thickness of bonds) is too large to maintain static properties of the standard DPD polymer. In the present study, for reducing $d_{\rm c}$ and artificial effects in SRP models, we propose a modification of the SRP model by using multipoint cites (mp-SRP) instead of single cite for bond-bond interactions. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R6.00013: High Throughput investigation of Tunable Thermoresponsive Polymers Jodi Mecca, Anurima Singh, Sara Ouellette, Jeff Mitchell Thermoresponsive polymers that display a low critical solution temperature (LCST) in water at temperatures between the freezing and boiling point of water are of interest in the development of smart materials. The most popular of these polymers in poly(N-Isopropylacrylamide); however it has been shown that polymers based on polyethylene glycol methacrylate (PEGMA) also display an LCST within this temperature range. The current work demonstrates that copolymers based on PEGMA and benzyl methacrylate (BzMA) show a highly tunable transition temperature. The presentation will describe the high throughput techniques used to synthesize and characterize the copolymers and the resulting understanding of the compositional dependence of the phase behavior of PEGMA/BzMA copolymers. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R6.00014: Re-entrance of Poly(N,N-diethylacrylamide) in D$_{\mathrm{2}}$O/d-Ethanol Mixture at 27 $^{\mathrm{o}}$C. He Cheng The re-entrance of poly(N,N-diethylacrylamide) (PDEA) in D$_{\mathrm{2}}$O/d-ethanol mixtures (i.e., the coil-to-spherical aggregates-to-coil transition) has been observed at 27 $^{\mathrm{o}}$C by small-angle neutron scattering (SANS). PDEA has a lower critical solution temperature (LCST) phase diagram in the D$_{\mathrm{2}}$O rich region and is soluble in the D$_{\mathrm{2}}$O-poor region for all of the observed temperature ranges. Its spinodal temperature decreases first from 33.5 $^{\mathrm{o}}$C in pure D$_{\mathrm{2}}$O to 26.7 $^{\mathrm{o}}$C in 80{\%} D$_{\mathrm{2}}$O/ 20{\%} d-ethanol and then increases to 283.1$^{\mathrm{o}}$C in 50{\%} D$_{\mathrm{2}}$O/50{\%} d-ethanol With the further decrease of D$_{\mathrm{2}}$O content, PDEA dissolves well, and its phase boundary can no longer be observed by SANS. The ternary random phase approximation model (RPA) is used to analyze the SANS profiles, and three Flory$-$Huggins interaction parameters ($\chi_{\mathrm{PDEAdethanol}}$, $\chi_{\mathrm{PDEAD2O}}$ and $\chi_{\mathrm{dethanolD2O}})$ are obtained. When a small amount of d-ethanol is added to the system, it has a strong interaction with D$_{\mathrm{2}}$O, so it directly gets distributed into the water structure and makes a negative contribution to the dissolution of PDEA ($\chi_{\mathrm{dethanolD2O}}$ is much smaller than$\chi_{\mathrm{PDEAdethanol}}$ and $\chi_{\mathrm{PDEAD2O}})$. Neither d-ethanol nor D$_{\mathrm{2}}$O wants to help the dissolution of PDEA in the first place, until the structure of mixed solvents tends to be pure d-ethanol in the D$_{\mathrm{2}}$O-poor region. [Preview Abstract] |
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