This paper introduces a systematic procedure to obtain well-relaxed atomistic melt structures from mesocale models of vinyl polymers based on sequences of diads. Following the methodology introduced by Milano and Müller-Plathe [J. Phys. Chem. B. 2005, 109, 18609], coarse-grain models consisting of sequences of superatoms of two different types meso and racemo have been used to relax mesocale melts of atactic and syndiotactic polystyrene. The proposed method, based on a fully geometrical approach, does not involve expensive potential energy and force evaluations and allows a very fast and efficient reconstruction of the atomistic detail. The method, successfully tested against experimental data, allows us to obtain all atom models of both stereoregular and stereoirregular polymers and opens the possibility of relaxing large molecular weight melts of vinyl chains.
Molecular dynamics simulations have been performed to obtain detailed all-atom models of the interface between polystyrene (PS) and gold nanoparticles. Considering their relevance in the memory technology, systems containing gold nanoparticle included in PS polymer melts also in the presence of 8-hydroxyquinoline (8-HQ) molecules have been studied. Four different systems, including a coated or a noncoated nanoparticle, have been compared. Calculated radial density profiles show that the presence of noncoated nanoparticles in a polymer melt causes an ordering of polymer chains. A similar ordering behavior is found for the 8-HQ molecule. In the presence of a coated gold nanoparticle, calculated radial density profiles show much less order. When 8-HQ is present, this molecule is closer to the nanoparticle surface and when in contact with a coated nanoparticle it shows a partial penetration into the thiols layer. The molecular description obtained from simulations supports some of the hypothesis made on the basis of the experimental behavior of nonvolatile memory devices.
The method of re-introducing atomistic detail into a coarse-grained polymer structure, so-called backmapping, is extended to a nonequilibrium situation. Problems in backmapping coarse-grained polymer models, on which a nonequilibrium shear flow has been imposed, are discussed. A backmapping protocol, where the globally deformed conformations are maintained during backmapping by applying position restraints, is proposed. The local optimization of the atomistic structure is performed in the presence of these restraints. The artifact of segment isolation introduced by position restraints is minimized by applying different restraint patterns iteratively. The procedure is demonstrated on the test case of atactic polystyrene under a steady shear flow.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.