Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y17: Focus Session: Multiscale Modeling in Polymeric Materials |
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Sponsoring Units: DPOLY DCOMP Chair: Michael Rubinstein, University of North Carolina, Chapel Hill Room: Colorado Convention Center 102 |
Friday, March 9, 2007 11:15AM - 11:51AM |
Y17.00001: Molecular Dynamics Simulations of Layer-by-Layer Assembly of Charged Macromolecules Invited Speaker: Molecular dynamics simulations of electrostatic assembly of multilayers of flexible polyelectrolytes and charged nanoparticles at a charged surface were performed. The multilayer build-up was achieved through sequential adsorption of oppositely charged macromolecules in a layer-by-layer fashion from dilute solutions. The steady state multilayer growth proceeds through a charge reversal of the adsorbed polymeric film, which leads to a linear increase in the polymer surface coverage after completion of the first few deposition steps. Moreover, substantial intermixing between chains adsorbed during different deposition steps is observed. This intermixing is consistent with the observed requirement for several deposition steps to transpire for completion of a single layer. However, despite chain intermixing, there are almost perfect periodic oscillations of the density difference between monomers belonging to positively and negatively charged macromolecules in the adsorbed film. Weakly charged chains show higher polymer surface coverage than strongly charged ones. [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:03PM |
Y17.00002: Dynamics of melts consisting of circular and linear polymers Michael Lang, Michael Rubinstein Recent experimental results indicate that small contaminations of linear polymers with 0.1\% volume fraction or less in ring polymer melts lead to dramatic changes in the rheology of the melt. These volume fractions are clearly below overlap concentration of the linear species. Thus, the experimental observations cannot be explained by a simple picture based on a percolating cluster of linear chains penetrating rings. The goal of our computer simulation studies of comparable systems is to solve this puzzle. We use the bond fluctuation method on a lattice as introduced by Carmesin and Kremer (Macromolecules 21, 2819-2823 (1988)) to model homopolymer melts ranging from 32 to 1024 monomers per chain. The volume fraction of linear polymer is varied from 1/16 to zero. We simulate small melts of 16384 monomers in order to have access to the long-time behavior of the samples. We will present and discuss simulation data on diffusion, ring and linear polymer conformations, mobility and contact statistics of different samples with varying volume fraction of linear polymer. [Preview Abstract] |
Friday, March 9, 2007 12:03PM - 12:15PM |
Y17.00003: Numerical Advances in Field Theoretic Simulations of Polymers Erin M. Lennon, Kirill Katsov, Hector D. Ceniceros, Carlos J. Garcia-Cervera, Glenn H. Fredrickson Field theoretic simulations have been very successful in predicting the mesoscopic behavior of polymer self-assembly in the mean-field limit. Nevertheless, studies beyond this approximation have been hindered by the numerical complexities of simulating a fluctuating field theory with a complex Hamiltonian. To address these problems, we have developed a suite of highly efficient numerical methods to study practically arbitrary polymer systems. Moreover, we further propose a thermodynamic integration technique suitable for determining the free energy of such field-based fluctuating systems. Using the standard diblock copolymer as our model system, we quantitatively investigate the effect of fluctuations on the order-disorder transition. [Preview Abstract] |
Friday, March 9, 2007 12:15PM - 12:27PM |
Y17.00004: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 12:27PM - 12:39PM |
Y17.00005: Multiscale modeling of self-assembling polymer solutions Dmitry Bedrov, Grant Smith, Ben Hanson We have applied a multiscale modeling approach to study complex self-assembling systems such as micellar solutions and biopolymer networks. In our multiscale modeling approach we start with quantum chemistry calculations to parameterize accurate fully atomistic force fields, perform extensive atomistic explicit solvent molecular dynamics simulations on model self-assembling building blocks in solutions to understand structure and thermodynamics at atomistic scale, parameterize coarse-grained implicit solvent models, conduct extensive implicit solvent model simulations to study the self-assembly, and use a self consistent field approach to predict the system morphology. Specifically, we applied this methodology to self-assembly of triblock (PEO-PPO-PEO, Pluronic) micelles as well as to network formation of polypeptide (leucine)-modified hyaluronic acid in aqueous solutions. [Preview Abstract] |
Friday, March 9, 2007 12:39PM - 12:51PM |
Y17.00006: Coarse grained model of polymer dynamics R.C. Picu, A. Rakshit A coarse grained representation of the structure and dynamics of polymer melts is developed. In the coarse grained model an entanglement segment is represented as a blob with a single degree of freedom. The inner blobs of the chain are constrained to perform random walks along the primitive path, while the chain end blobs have three degrees of freedom and interact through a non-bonded potential with all other blobs of the system. The primitive path is initially calibrated from the fine, atomistic system and then evolves as dictated by the kinematics of the end blobs. The inter-blob bonded and non-bonded potentials are calibrated from the fine model to reproduce the chain structure statistics. The coarse system is evolved with Brownian dynamics using a monomeric friction which is computed from the fine system. Constraint release is introduced and is dictated by an error indicator that monitors the neighborhood of a given primitive path segment during the simulation. The only parameter which is not necessarily (but it may be) calibrated from the fine model is the characteristic entanglement segment length. The coarse model predictions are compared with full atomistic simulation results. [Preview Abstract] |
Friday, March 9, 2007 12:51PM - 1:03PM |
Y17.00007: Multiscale Simulation of polyethylene oxide: Combined United Atom and Coarse-Grained Modeling Praveen Depa, Janna Maranas We present combined united atom [UA] and coarse-grained [CG] molecular dynamics simulations of polyethylene oxide [PEO]. A hybrid region is used to connect united atom and coarse-grained regions, allowing them to occupy different spatial locations in the same simulation box. The presence of a hybrid region allows for a smooth and continuous change in the description of an interacting particle from a coarse-grained bead to a united atom and vice versa. This multiscale simulation is tested with united atom PEO and a coarse-grained model of PEO developed in our group. In the coarse-grained model each CG bead consists of six united atoms and the interactions between them are parameterized to accurately represent static properties, defined by the UA simulations and verified by experiments. Employing the hybrid region in the multiscale simulation works well, as evidenced by good agreement between static properties from the multiscale simulation with those from all UA and all CG simulations. We investigate the performance of the multiscale simulation when addressing dynamics properties, by comparing to UA and CG simulations, and experiments. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:15PM |
Y17.00008: Structure and Evolution of Ordered Domains in Deeply Quenched Polyethylene Melt Naida Lacevic, Laurence Fried, Richard Gee Solidification of polymeric materials strongly depends on how the melt is cooled below its crystallization temperature. If cooling is at moderate rates, the most common and well understood mechanism is via nucleation and growth of spherulites, but special cases exist where crystallization is preceded by a pre-transition state induced by density fluctuations. Such multi-step crystallization scenarios are suggested by many experiments, and recent theoretical and simulation work. In this special case, the melt is quenched into a metastable region and the transition from the disordered phase to an ordered phase is uniform in contrast to the classical nucleation and growth mechanism. In this study we investigate this continuous transition. We have conducted the largest and longest timescale simulations of polyethylene to date. These elucidate the initial separation of a metastable, mesomorphic phase. Via energetic and geometric analyses, we have examined the structure of mesomorphic domains and the dynamics of their formation and evolution, including atomic scale details of molecular addition to ordered domains, as well as particle dynamics in the system, including high mobility jumps in the ordered domains at wavelengths matching the monomer spacing. [Preview Abstract] |
Friday, March 9, 2007 1:15PM - 1:27PM |
Y17.00009: Simulating the Oxidation of Polypropylene Using a Reactive Forcefield Joanne Budzien, Aidan Thompson Oxidation of organic materials is a problem for seals and membranes in many environments. Any particular instance of a chemical reaction is fast with purely local effects. Over longer times, the cumulative effect of many reactions results in large changes in average stress, strain, and other macroscopic properties of the sample. We have had some success in developing constitutive models for rubber, which connect the topology of the network with the observed stress during aging under strain. As the next phase of the project, we have performed simulations using a reactive forcefield to examine the atomistic changes during oxidation. Results will be presented for polypropylene and compared with experimental data for labeled samples undergoing oxidation. [Preview Abstract] |
Friday, March 9, 2007 1:27PM - 1:39PM |
Y17.00010: Rheological properties of polymer melts in confined shear flow from dynamic Monte Carlo simulations. John Dorgan The viscoelastic properties of dense polymer melts in shear flow are examined using dynamic Monte Carlo simulation for plate spacings less than 10 times the molecular radius of gyration. The coarse graining methodology employed consists of the cooperative motion algorithm of Pakula and a derived biasing technique based on previous studies of Binder and Baushnagel. For relatively large plate spacings and slow flows, a uniform linear velocity profile is obtainable. Use of the Kramers form for entropic springs allows the calculation of stress in the simulation providing a means for exploring rheological properties including viscosity and normal stress differences. Results are in excellent agreement with well-established experimental facts; a shear thinning viscosity is obtained, the first normal stress difference increases with shear rate, and the first normal stress coefficient decreases with shear rate. Evidence of entanglements are present for longer chain lengths. For fast flows, the linear velocity profile is lost and shear banding is observed. A non-monotonic stress with shear rate is found in conjunction with the shear banding and mechanistically this is attributable to a cohesive failure with an excess of chain ends being found at the slip plane. Results for variable plate spacings shed some insight into novel confinement effects that are being exploited in emerging areas of nanotechnology. [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 1:51PM |
Y17.00011: Flow-deformed conformations of entangled polymers as persistent random walks Yitzhak Shnidman Modeling interfacial phenomena in polymer fluids requires resolution of chain conformations on the Kuhn length scale. If the chains are at thermodynamic equilibrium, or undergo flow deformation in the unentangled regime, this is accomplished by representing chain conformations as Wiener (uncorrelated) random walks. When \textit{entangled} chains are deformed by flow, stretching and orientation of chain \textit{strands} between successive entanglements entails \textit{inertial}, as well as diffusive, aspects in the anisotropic propagation model for strand conformation. This is best captured by a \textit{persistent} (correlated) random walk at constant speed, which is a second-order Markov process governed by the initial probabilities and the scattering rates for the velocities. We present here a generalized Green-Kubo relation linking these parameters to the second moment of the strand's end-to-end distance. The latter evolves according to an approximate differential equation coupling local flow deformation rate with strand stretching and orientation, which relax on distinct time scales [G. Marrucci and G. Ianniruberto, \textit{Phil. Trans. R. Soc. Lond. A} \textbf{361}, 677 (2003)]. The proposed relation provides a cornerstone for a new \textit{entangled} version of our dynamic self-consistent field theory, that thus far has been limited to unentangled inhomogeneous polymer fluids [M. Mihajlovic, T. S. Lo, and Y. Shnidman, \textit{Phys. Rev. E} \textbf{72}, 041801 (2005)]. [Preview Abstract] |
Friday, March 9, 2007 1:51PM - 2:03PM |
Y17.00012: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 2:03PM - 2:15PM |
Y17.00013: DNA-Particle Hydrodynamic Interactions In Microchannels Yeng-Long Chen The hydrodynamic contribution to the dynamics of DNA - particle mixtures in microfluidic channels is important for phenomena such as DNA/particle aggregation and DNA conformation change. Recent simulation and experimental works have successfully showed the importance of hydrodynamic contributions to the dynamics of DNA migration away from microchannel walls in a pressure-driven flow. In this work, we investigate the interplay between particle and DNA hydrodynamics by employing the lattice Boltzmann method (LBM) and coarse-grained Brownian dynamics. In addition, particle-DNA hard core interactions also affect the conformation and the dynamics of the flexible DNA molecule. The roles of particle / DNA size asymmetry and DNA and particle concentrations on the dynamic properties of the solution are systematically investigated. [Preview Abstract] |
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