Molecular dynamics study on structural evolution and interfacial interactions of Ca 2+ -crosslinked alginate-silica composite gels for polishing applications

Molecular dynamics simulations reveal the encapsulation mechanism of silica particles within Ca²+-crosslinked alginate composites. Ca²+ forms stable bidentate coordination with carboxyl groups, constructing a three-dimensional network with favourable structural stability at a specific Ca²+ to carboxyl molar ratio within the studied conditions. A three-tiered mechanism involving physical confinement, negligible Ca²+–SiO₂ coordination, and noncovalent interactions is proposed to contribute to the immobilisation of silica particles under the simulation conditions. The crosslinked network spatially restricts particle motion. Moderate particle loading improves network compactness, whereas excessive or oversized particles weaken crosslinking efficiency through steric hindrance. Hydrogen bonding and van der Waals interactions contribute to reversible adsorption and dynamic interfacial stabilisation. Particle concentration and size further modulate the network microstructure and interfacial characteristics. Compared with chemically bonded and free abrasive systems, the gel-encapsulated system presents restricted particle mobility and enhanced mechanical stability compared with the two reference systems. This work provides molecular-level insights into interfacial coupling and regulated particle behaviour in soft gel composite systems.