A Comprehensive MARTINI Coarse-Grained Framework for Phyllosilicate Clay/Polymer Nanocomposites: From Atomistic Validation to Mesoscale Insights

TL;DR

This paper introduces a detailed coarse-grained MARTINI model for phyllosilicate clay/polymer nanocomposites, validated against atomistic simulations and used to explore mesoscale properties and morphology relevant for material design.

Contribution

The study develops and validates a MARTINI-3 coarse-grained model for pyrophyllite and montmorillonite, enabling mesoscale simulations of clay/polymer nanocomposites with accurate property predictions.

Findings

Validated CG model reproduces atomistic radial distribution functions.

Demonstrated clay's effect on polymer dynamics and morphology.

Reduced interfacial tension in TPS-PE composites with clay presence.

Abstract

Phyllosilicate clays have diverse applications in packaging industries and are found highly suitable for formulation, including thermoplastic starch (TPS), polyethylene (PE), or their combination. We developed CG MARTINI-3 parameters of the pyrophyllite using Lifshitz theory and experimental surface tension data. These initial bead assignments of pyrophyllite and periodic tetramethylammonium-montmorillonite (TMA-MMT) sheet were fine-tuned using optimal reproduction of structural, thermodynamic, and dynamic properties obtained via all-atom (AA) simulation of TPS with a periodic pyrophyllite sheet. These developed models predicted the correct AA radial distribution function and two-body excess entropy for polymer-sorbitol pairs, showcasing the robustness of the developed CG model in predicting the properties not used in parameterization. These composite simulations revealed acceleration (for pyrophyllite) or retardation (for TMA-MMT) of khun segment dynamics (compared to melt) with the depletion of polymer near the surface. The developed CG parameters were used to investigate the long-time behavior of TPS-polyethylene (PE) melt and their Cloisite-15A-based composite systems. The coordination number indicated compatibilization of the TPS-PE phase, achieved by binding TPS through its bare polar surface and PE via alkyl-mediated interactions, which consequently reduced the TPS-PE interfacial surface tension from 45 mN/m to 13.06 mN/m. Additionally, high TPS-clay coordination, sustained localization of clay at the TPS-PE interface, and clay aggregation observed in CG simulation closely agree with experimental observations. Further, the CG model effectively captured the clay-mediated variation in the overall morphology of the TPS-PE system and their direct impact on chain conformational properties, making this CG model highly suitable for a material design perspective.