Characterization of Morphology Evolution in a Polymer-Clay Nanocomposite using Multiscale Simulations

TL;DR

This study develops a multiscale simulation approach to investigate the morphology evolution and structure-property relationships in polymer-clay nanocomposites, providing insights into how clay arrangement influences polymer behavior.

Contribution

A new coarse-grained model compatible with MARTINI force field enables efficient simulation of polymer-clay nanocomposites, accurately capturing structural and dynamical properties.

Findings

CG model achieves less than 4% deviation from all-atom simulations

Clay arrangement affects polymer reorientation and assembly

Clay acts as a neutral surface influencing polymer behavior

Abstract

Molecular simulations provide an effective route for investigating morphology evolution and structure-property relationship in polymer-clay nanocomposites (PCNCs) incorporating layered silicates like montmorillonite (MMT), an important class of materials that show a significant enhancement over the constituent polymer for several properties. However, long relaxation times and large system size requirements limit the application to systems of practical interest. In this work, we have developed a coarse-grained (CG) model of organically modified MMT (oMMT) compatible with the MARTINI force field, a chemically-specific interaction model with high transferability. The dispersive and polar components of cleavage energy, basal spacing, and mechanical properties of MMT with tetramethylammonium (TMA) as intergallery ions were used to obtain a rational estimate for clay particle MARTINI bead types in accordance with the polarity of the functional group. The CG model provided accurate concurrent estimates for the structural, thermodynamic, and dynamical properties of PE in a PE/TMA-MMT PCNC, with less than 4% deviation from all atom (AA) simulations. The slow clay-induced redistribution of the PE-b-PEG block copolymer in the PCNCs was investigated using the developed CG model, with conformational changes occurring over a microsecond timescale. The preferential interaction coefficient and cluster analysis of individual blocks of PE-b-PEG were used to study the effect of clay arrangement (exfoliated versus tactoid) on copolymer reorientation and assembly at the clay surface. We find that the oMMT coated with PE-b-PEG acts as a neutral surface (small difference in polymer-polymer and polymer-oMMT+PE-b-PEG enthalpic interactions) and the primary influence of the nanofiller is a result of confinement and steric effect of the clay sheets on the PE chains.