Coarse-grained dynamics of one chain in a polymer melt

2000 ◽  
Vol 113 (15) ◽  
pp. 6409-6422 ◽  
Author(s):  
Reinier L. C. Akkermans ◽  
W. J. Briels
Keyword(s):  
Polymer Melt ◽  
Coarse Grained

scholarly journals Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films

2018 ◽  
Vol 115 (22) ◽  
pp. 5641-5646 ◽  
Author(s):  
Wengang Zhang ◽  
Jack F. Douglas ◽  
Francis W. Starr
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Polymer Films ◽  
Interaction Strength ◽  
Polymer Melt ◽  
Dynamic Structure ◽  
Coarse Grained ◽  
Implicit Assumption ◽  
Simple Method ◽  
Thin Polymer

There is significant variation in the reported magnitude and even the sign of Tg shifts in thin polymer films with nominally the same chemistry, film thickness, and supporting substrate. The implicit assumption is that methods used to estimate Tg in bulk materials are relevant for inferring dynamic changes in thin films. To test the validity of this assumption, we perform molecular simulations of a coarse-grained polymer melt supported on an attractive substrate. As observed in many experiments, we find that Tg based on thermodynamic criteria (temperature dependence of film height or enthalpy) decreases with decreasing film thickness, regardless of the polymer–substrate interaction strength ε. In contrast, we find that Tg based on a dynamic criterion (relaxation of the dynamic structure factor) also decreases with decreasing thickness when ε is relatively weak, but Tg increases when ε exceeds the polymer–polymer interaction strength. We show that these qualitatively different trends in Tg reflect differing sensitivities to the mobility gradient across the film. Apparently, the slowly relaxing polymer segments in the substrate region make the largest contribution to the shift of Tg in the dynamic measurement, but this part of the film contributes less to the thermodynamic estimate of Tg. Our results emphasize the limitations of using Tg to infer changes in the dynamics of polymer thin films. However, we show that the thermodynamic and dynamic estimates of Tg can be combined to predict local changes in Tg near the substrate, providing a simple method to infer information about the mobility gradient.

scholarly journals Quantitative relations between cooperative motion, emergent elasticity, and free volume in model glass-forming polymer materials

2015 ◽  
Vol 112 (10) ◽  
pp. 2966-2971 ◽  
Author(s):  
Beatriz A. Pazmiño Betancourt ◽  
Paul Z. Hanakata ◽  
Francis W. Starr ◽  
Jack F. Douglas
Keyword(s):  
Free Volume ◽  
Glass Formation ◽  
Collective Motion ◽  
Configurational Entropy ◽  
Polymer Melt ◽  
Polymer Materials ◽  
Coarse Grained ◽  
Glass Forming ◽  
Cooperative Motion ◽  
Glass Forming Materials

The study of glass formation is largely framed by semiempirical models that emphasize the importance of progressively growing cooperative motion accompanying the drop in fluid configurational entropy, emergent elasticity, or the vanishing of accessible free volume available for molecular motion in cooled liquids. We investigate the extent to which these descriptions are related through computations on a model coarse-grained polymer melt, with and without nanoparticle additives, and for supported polymer films with smooth or rough surfaces, allowing for substantial variation of the glass transition temperature and the fragility of glass formation. We find quantitative relations between emergent elasticity, the average local volume accessible for particle motion, and the growth of collective motion in cooled liquids. Surprisingly, we find that each of these models of glass formation can equally well describe the relaxation data for all of the systems that we simulate. In this way, we uncover some unity in our understanding of glass-forming materials from perspectives formerly considered as distinct.

Quantitative Model for Clusters of String-like Cooperative Motion in a Coarse-Grained Glass-Forming Polymer Melt

2014 ◽  
Vol 1622 ◽  
pp. 95-111 ◽  
Author(s):  
Beatriz A Pazmiño Betancourt ◽  
Jack F. Douglas ◽  
Francis W. Starr
Keyword(s):  
Configurational Entropy ◽  
Polymer Melt ◽  
Quantitative Model ◽  
Coarse Grained ◽  
Residual Entropy ◽  
Arrhenius Behavior ◽  
String Length ◽  
Glass Forming ◽  
Free Parameters ◽  
Lower Temperature

ABSTRACTWe apply a living polymerization theory to describe cooperative string-like particle rearrangement clusters observed in simulations of a coarse-grained polymer melt. The theory quantitatively describes the interrelation between the average string length L, configurational entropy Sconf, and the order parameter for string assembly Φ without free parameters. Combining this theory with the Adam-Gibbs (AG) model allows us to predict the relaxation time τ in a lower temperature T range than accessible by current simulations. In particular, the combined theories suggest a return to Arrhenius behavior near Tg and a low T residual entropy, thus avoiding a Kauzmann ‘entropy crisis’.

scholarly journals Predictive relation for the α-relaxation time of a coarse-grained polymer melt under steady shear

2020 ◽  
Vol 6 (17) ◽  
pp. eaaz0777 ◽  
Author(s):  
Andrea Giuntoli ◽  
Francesco Puosi ◽  
Dino Leporini ◽  
Francis W. Starr ◽  
Jack F. Douglas
Keyword(s):  
Relaxation Time ◽  
Structural Relaxation ◽  
Polymer Melt ◽  
Steady Shear ◽  
Coarse Grained ◽  
Scattering Function ◽  
Dynamic Heterogeneity ◽  
Shear Rates ◽  
Wide Range ◽  
Intermediate Scattering Function

We examine the influence of steady shear on structural relaxation in a simulated coarse-grained unentangled polymer melt over a wide range of temperature and shear rates. Shear is found to progressively suppress the α-relaxation process observed in the intermediate scattering function, leading ultimately to a purely inertially dominated β-relaxation at high shear rates, a trend similar to increasing temperature. On the basis of a scaling argument emphasizing dynamic heterogeneity in cooled liquids and its alteration under material deformation, we deduce and validate a parameter-free scaling relation for both the structural relaxation time τα from the intermediate scattering function and the “stretching exponent” β quantifying the extent of dynamic heterogeneity over the entire range of temperatures and shear rates that we can simulate.

scholarly journals Influence of Branching on the Configurational and Dynamical Properties of Entangled Polymer Melts

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 1045 ◽  
Author(s):  
Alexandros Chremos ◽  
Jack F. Douglas
Keyword(s):  
Correlation Function ◽  
Molecular Mass ◽  
Polymer Melts ◽  
Pair Correlation ◽  
Polymer Melt ◽  
Coarse Grained ◽  
Density Correlation ◽  
Glass Forming ◽  
Entangled Polymer ◽  
Simulation Results

We probe the influence of branching on the configurational, packing, and density correlation function properties of polymer melts of linear and star polymers, with emphasis on molecular masses larger than the entanglement molecular mass of linear chains. In particular, we calculate the conformational properties of these polymers, such as the hydrodynamic radius R h , packing length p, pair correlation function g ( r ) , and polymer center of mass self-diffusion coefficient, D, with the use of coarse-grained molecular dynamics simulations. Our simulation results reproduce the phenomenology of simulated linear and branched polymers, and we attempt to understand our observations based on a combination of hydrodynamic and thermodynamic modeling. We introduce a model of “entanglement” phenomenon in high molecular mass polymers that assumes polymers can viewed in a coarse-grained sense as “soft” particles and, correspondingly, we model the emergence of heterogeneous dynamics in polymeric glass-forming liquids to occur in a fashion similar to glass-forming liquids in which the molecules have soft repulsive interactions. Based on this novel perspective of polymer melt dynamics, we propose a functional form for D that can describe our simulation results for both star and linear polymers, covering both the unentangled to entangled polymer melt regimes.

Mesoscale model of polymer melt structure: Self-consistent mapping of molecular correlations to coarse-grained potentials

2005 ◽  
Vol 122 (10) ◽  
pp. 104908 ◽  
Author(s):  
Henry S. Ashbaugh ◽  
Harshit A. Patel ◽  
Sanat K. Kumar ◽  
Shekhar Garde
Keyword(s):  
Mesoscale Model ◽  
Polymer Melt ◽  
Coarse Grained ◽  
Melt Structure ◽  
Self Consistent ◽  
Consistent Mapping
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