Tailoring Interfacial Properties in Polymer–Silica Nanocomposites via Surface Modification: An Atomistic Simulation Study

Abstract

Surface modification is an effective way to improve the dispersion of nanofillers in a polymer matrix and tune the interfacial interactions that determine macroscopic properties in polymer nanocomposites. In this work, we present a detailed investigation of silane modification effects on polymer interfacial conformation and dynamic properties through atomistic molecular dynamics simulations, using cis-1,4 polyisoprene (the major component of natural rubber) and amorphous silica substrate as a model system. Industrially relevant modified substrates are constructed with alkylsilane agents grafted at different surface densities. Contrasting systems with the modified substrates to the bare substrate case, we show that silane grafting effectively modulates chain conformations near the silica surface in terms of train, loop, and tail configurations, highlighting the separate effects of silane grafting density and agent chain length. We examine the variation of polymer dynamics in desorption, relaxation, and diffusion, which demonstrates the weakening of dynamic slowing down at the interface due to the silane presence and further exposes the dominant effects of surface train segments on the dynamic properties. Our results offer microscopic information on interfacial behavior while identifying key factors for tailoring interfacial dynamics. These findings provide useful insight into the reinforcement mechanism and serve as a first step toward the rational design of rubber composite materials via chemically detailed computational modeling.

Dynamics of Long Entangled Polyisoprene MeltsviaMultiscale Modeling

“…Simulations at different temperatures may require further refinement of the models and, more importantly, time-scaling mapping (related to friction) . Our coarse graining methodology presents significant potential for applications to systems with higher complexity, such as random copolymers and composite materials, ,,− which will be the focus of future studies.…”

“…Each PI monomer comprises five united atoms, corresponding to CH 2 , C, CH, CH 2 , and CH 3 with the mass of 14.027, 12.011, 13.019, 14.027, and 15.035 Da, respectively. The UA force field was adopted from previous studies showing quantitative agreement with experimental findings on lower molecular weight systems. ,,,, …”

“…The UA force field was adopted from previous studies showing quantitative agreement with experimental findings on lower molecular weight systems. 55,56,59,69,70 A moderately CG model was employed as previously developed based on the UA model, 61 using one CG bead to represent a monomeric repeating unit. The position of the CG bead was mapped to the center of mass of each repeat unit to maintain a consistent description of chain ends with a single interaction type.…”

“…Atomistic models of PI have only been employed to study local and chain relaxation of oligomers (for example, M < 2000 g/mol; for PI, the molecular weight (MW) of a repeat unit M 0 ≈ 68.1 g/mol) − due to significant challenges in capturing the slower dynamics compared to PE and PB. An alternate route consists of the development of systematically coarse-grained (CG) chemistry-specific models that can efficiently address properties of PI at the cost of a reduced resolution. ,, Such an approach was previously applied to systems like polystyrene melts to probe the crossover to entangled dynamics that is challenging to explore in full atomistic detail. , Li and co-workers developed PI CG models for constant-density simulations based on atomistic descriptions of N = 10 mer long oligomers.…”

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

“…The authors then reported structural and dynamical properties, such as chain dimensions and the relaxation of the end-to-end vector for the chemistry-specific coarse-grained model [51]. Amorphous silica substrates were also used to confine the polyisoprene chains in thin films [52,53]. In their study, Guseva et al investigated the effect of the film thickness and, thus, of the imposed confinement, reporting mainly the overall properties of the material averaged over the whole film [52].…”