Interfacial Adsorption Enhancement between C–S–H and Microcapsule Walls (Ethyl Cellulose/SiO ₂ ): Mechanisms from Molecular Dynamics and Experiments

To meet the growing demand for high-performance self-healing microcapsules in cementitious systems, it is essential to refine microcapsule wall architectures. This study elucidates the microscopic adsorption enhancement mechanism of modified double-layer microcapsule wall materials using molecular dynamics (MD) simulations, combined with adsorption experiments detected by ultraviolet–visible (UV–vis) spectroscopy. Ethyl cellulose (EC) serves as the primary wall component, and tobermorite (11 Å) is employed as a crystalline analog of calcium silicate hydrate (C–S–H). Comprehensive analyses of adsorption energy, structural deformation, atomic diffusion, and tensile response were performed. The computational framework was validated by comparing simulated adsorption energies and glass transition temperature (Tg) with experimental benchmarks. Critically, interfacial hydrogen-bond dynamics were identified as the predominant factor governing variations in adsorption energy, with molecular structural reorganization directly modulating adhesion efficacy. Spatially resolved diffusion trajectories further revealed that the spatial distribution of molecular components within the wall architecture significantly influences both the diffusion range and kinetics of tobermorite species. Nanoindentation tests and tensile simulations demonstrated consistent mechanical integrity across different wall configurations. These findings establish a mechanistic understanding of adsorption enhancement in double-layer microcapsules, providing design principles for engineering microcapsules with optimized durability and self-healing functionality for sustainable concrete infrastructure.