Interfacial rearrangement and nanomechanics of confined droplets stabilized by Janus and polymer-grafted nanoparticles

Despite extensive research on Pickering emulsions, the influence of interfacial organization near solid walls, and the distinct mechanical roles of Janus nanoparticles (NPs) versus polymer-grafted nanoparticles (GNPs) under confinement, remains incompletely understood. In this study, coarse-grained molecular dynamics simulations of Pickering droplets were used to clarify how nanoparticle architecture and interfacial coverage govern nanomechanical response during compression against a solid wall. The droplets were stabilized either by Janus NPs or by GNPs and compressed between a solid wall and a virtual planar indenter. For Janus NP-stabilized droplets, compressive stability cannot be predicted solely from the conventional static indicator based on droplet asphericity because droplets with similar asphericity at rest can fail at markedly different stresses. Instead, the number and spatial distribution of uncovered patches on the wall-facing interface dictate both the failure stress and the rupture pathway. In contrast, GNPs suppress persistent uncovered patches because the grafted polymer brushes generate steric repulsion and spread along the interface. This greatly reduces sensitivity to particle arrangement near the wall and yields consistently higher compressive strength than Janus NP-stabilized droplets at comparable surface coverage. By varying the grafting density, we show that low densities permit strong lateral compaction of the adsorbed layer, producing sharp stress peaks, whereas higher densities lead to smoother, more collective deformation with limited rearrangement. These insights provide concrete molecular-level design principles for tuning interfacial assembly to achieve mechanically robust Pickering emulsions in applications such as drug delivery, microfluidic transport, and flow through porous media. • Wall-side NP coverage topology dictates Pickering droplet failure pathways. • GNPs suppress uncovered patches and boost compressive stability. • Janus NP droplets fail differently despite similar static asphericity. • Grafting density tunes lateral compaction and stress overshoot.