How to evaluate the interaction between epoxy and a free surface via metadynamics: A coarse-grained example

Molecular investigations into polymer-surface interactions are essential for understanding and optimizing the mechanical behavior of, e.g., adhesive joints or polymer nanocomposites. In this context, metadynamics provides a powerful tool for determining the free energy of a molecular system through Gaussian sampling. While the literature demonstrates that metadynamics is well suited for adherend–adhesive systems, there is little discussion on the choice of the metadynamics parameters and their impact on the resulting free energy. This contribution provides a step-by-step methodology for determining the parameters of metadynamics, specifically the Gaussian’s depth, width, and deposition time, as well as the convergence. To illustrate this process, we utilize a simple coarse-grained system made up of a rigid substrate and either an epoxy or hardener molecule. Once we establish the optimal metadynamics parameters, we examine the effects of non-bonded polymer-surface interactions, which are modeled using 12-6 Lennard–Jones potentials, on the resulting free energy surface. As expected, we find that the distance parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ps</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> influences both the position and depth of the free energy well, while the energy parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ps</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> only affects the well depth. The methodology outlined here can be applied to more complex systems, making this article a useful guide for advanced studies on adhesive joints and polymer surface interactions in general.