Coupling between Polymer Conformations and Dynamics Near Amorphous Silica Surfaces: A Direct Insight from Atomistic Simulations

Abstract

The dynamics of polymer chains in the polymer/solid interphase region have been a point of debate in recent years. Its understanding is the first step towards the description and the prediction of the properties of a wide family of commercially used polymeric-based nanostructured materials. Here, we present a detailed investigation of the conformational and dynamical features of unentangled and mildly entangled cis-1,4-polybutadiene melts in the vicinity of amorphous silica surface via atomistic simulations. Accounting for the roughness of the surface, we analyze the properties of the polymer chains as a function of their distance from the silica slab, their conformations and the chain molecular weight. Unlike the case of perfectly flat and homogeneous surfaces, the monomeric translational motion parallel to the surface was affected by the presence of the silica slab up to distances comparable with the extension of the density fluctuations. In addition, the intramolecular dynamical heterogeneities in adsorbed chains were revealed by linking the conformations and the structure of the adsorbed chains with their dynamical properties. Strong dynamical heterogeneities within the adsorbed layer are found, with the chains possessing longer sequences of adsorbed segments (“trains”) exhibiting slower dynamics than the adsorbed chains with short ones. Our results suggest that, apart from the density-dynamics correlation, the configurational entropy plays an important role in the dynamical response of the polymers confined between the silica slabs.

Structure and Dynamics of a Polybutadiene Melt Confined between Alumina Substrates

“…In general, the behavior of polymer chains at interfaces is governed, by the strength of adsorption, the topological constraints imposed by other chains, such as entanglements, as well as the structure and the conformational heterogeneities of the adsorbed chains . Moreover, for systems with strong attractive polymer/substrate interactions, adsorbed chains might exhibit “glassy dynamics”, even at temperatures well above the glass transition, as observed both by simulations , and experiments . The slower relaxation modes inherited by attractive interfaces implicitly increase the necessary computational costs for studying such systems since more extended simulations are needed.…”

“…This is, in general, one of the most challenging tasks for atomistic simulations, since such interactions are typically the result of complex (many-body) physico-chemical phenomena, of quantum mechanical origin. In various studies, polymer/substrate interactions are described via the traditional Lorentz–Berthelot (LB) mixing rules, ,− or similar combination rules, such as the ones used by the COMPASS force-field (FF), − due to their simplicity. Nevertheless, such semi-empirical functional forms are rather crude approximations, particularly for modeling the complex metal/polymer interfacial interactions .…”

“…For this, accurate information about the behavior of polymer chains at the vicinity of the polymer/substrate interface at the molecular level is necessary. In this aspect, computational studies, and especially atomistic (classical) molecular dynamics (MD) simulations, can be a valuable tool to provide information about the structure and dynamics of polymer chains at the interface, that is typically inaccessible by experimental measurements, mainly due to its small width (typically of a few nm) and the amorphous structure of most polymers. − In order to reduce the computational cost, several MD simulation studies of polymers under confinement use either bead-spring or more systematic, coarse-grained models. ,− Such models provide a qualitative picture of the dynamical behavior of polymers under confinement; for example, a common finding is a dramatic reduction in chain mobility near strongly attractive walls but an enhancement near weakly adsorbing walls. Generic bead spring models can also be particularly helpful in examining a range of characteristics in polymer melts, particularly for length scales larger than about the Kuhn segment, since these are designed to follow the essentials of polymer physics .…”

Sensitivity Analysis of the Catalysis Recombination Mechanism on Nanoscale Silica Surfaces

“…Cui et al [ 39 , 40 ] studied the effects of the incident angle of AO, energy flux density, the number of graphene layers, and the surface morphology on the ablation, and found that the surface morphology had a significant effect on the ablation rate. Bačová et al [ 41 ] presented an investigation of dynamics relations in thick films of cis-polybutadiene chains placed between rough amorphous silica slabs. The results suggested that the monomeric translational motion parallel to the surface was affected by the presence of the silica slab.…”