Atomistic Monte Carlo simulation and continuum mean field theory of the structure and equation of state properties of alkane and polymer melts

Variable-Connectivity Monte Carlo Algorithms for the Atomistic Simulation of Long-Chain Polymer Systems

“…CONROT can be used in any constant-temperature ensemble (canonical, isothermal-isobaric [22,30,31], grand canonical, Gibbs, f 1 N 2 P T [32]). The original application [22] involved NP T simulations of oligomeric liquids of polyethylene in a united-atom representation using a combination of CON-ROT and reptation moves, but since then the move has been used for many other polymers, including atactic, isotactic, and syndiotactic polypropylene [22,33], cis-1,4 polyisoprene [34,35], trans-1,4 polyisoprene [36], cis-1,4 polybutadiene and 1,2 polybutadiene [36].…”

“…It is not sufficient, however, for equi-librating structural features at large length scales, such as the end-to-end distance and the radius of gyration, in systems of long chains. This became obvious in the original NP T simulations of oligomeric polyethylene melts with a MC algorithm using CONROT and reptation moves; the algorithm could fully equilibrate a C 24 , but not a C 78 melt [30].…”

“…3.7 , the centre of mass of a given chain executes a random walk [18,30]. (c) Truncated Gaussian distribution in the window of chain lengths [18,30]. (Reproduced from [29], with permission).…”

“…similar to those of isolated single chains subject only to local interactions along their backbones. Computer simulations [30,29,21] were instrumental in showing that, for PE, this hypothesis is true down to the atomistic level, if "local interactions" are appropriately defined. Torsion angle distributions, intramolecular pair density functions, and chain dimensions are practically indistinguishable between atomistically simulated PE melt chains and single chains subject to the same potentials but devoid of any nonbonded interactions between methylene or methyl segments separated by more than four bonds along their backbone.…”

Chameleon: A generalized, connectivity altering software for tackling properties of realistic polymer systems

“…The following equation describes the probability density in the conformational space for the case of a mixture of m components on which configuration sampling is attempted during the simulation: The simulations performed in the aforementioned ensembles are gathered in Chameleon under a unified environment termed MELT. However, in addition to the realistic MELT MC calculations, the Chameleon engine incorporates a fast sampling technique for continuous unperturbed chain (CUC) [22][23][24] calculations as representative of the conformations adopted by chains in the amorphous bulk. In the spirit of Flory's Rotational Isomeric State (RIS) model 25 which postulates that the conformations of polymer chains in the bulk are determined on average by short-range intramolecular interactions and are unperturbed by long-range interactions, our CUC model includes only local interactions (bond angle bending, torsional, and intramolecular nonbonded (Lennard-Jones) between sites four bonds apart (pentane-effect)).…”