In recent years, jointing materials using adhesive gathers much attention because this enables to joint with lightweight even for different materials. Not only laboratory experiments but molecular simulations are performed for understanding properties related to adhesion. One of the applications of molecular simulations to adhesion problems is precise evaluation of the adhesion strength. Adhesion strength is quantitatively evaluated via the work of adhesion, which is defined by subtracting the interfacial free energy from the sum of surface free energies of each materials. Therefore, the free energy calculation using molecular simulation plays a key role for quantitative evaluation of adhesion strength.<br/><br/> For solid-liquid interface, several methods for evaluating interfacial free energy have already been proposed. Interfacial free energy can be obtained by integrating the free energy gradient, which is evaluated via molecular simulation, in the process of separating liquid atoms from the solid surface. Separation of liquid atoms can be done by applying artificial planar potential which acts on liquid atoms at the interface. Then, this potential is gradually shifted along the direction perpendicular to the interface. Although, this method works well when the solid surface is sufficiently flat, there is inefficiency if this method is applied to complex surfaces such as polymer grafted substrates, e.g., the planar potential should be shifted over long distance.<br/><br/> We developed the novel method to evaluate the work of adhesion using molecular simulation to improve this inefficiency. In this method, a set of spherical potentials instead of planar potential is introduced to separate liquid atoms from the solid surface according to its structure. This enables to reduce the number of evaluations of the free energy gradient. In addition, we considered the update scheme of parameters contained in potentials to suppress the variation in the free energy gradient, which contributes improvement of the accuracy of numerical integration. Then, we found that the parameters to suppress the variation in the free energy gradient can be adaptively determined. Therefore, this method can be applied without dependence on species of solid and liquid.

Novel evaluation scheme of adhesion strength at the interface between liquid and polymer-grafted substrate

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.