Interfacial behaviour of hairy nanoparticle droplets on atomically smooth to physically patterned rough surfaces

Hairy nanoparticles (HNPs), consisting of a nanoparticle core with grafted polymer chains, exhibit complex bulk and interfacial behavior due to the intricate interplay between chain conformations and interactions between them. In this study, molecular dynamics simulations are employed to systematically investigate the influence of interaction strength on the structural, dynamical, and wetting properties of HNPs. In the bulk phase, increasing segment-segment (monomer) interaction strength leads to a non-monotonic structural transition, in which HNPs evolve from extended to compact and then re-expand conformations. This behavior is quantified using radial distribution functions, radius of gyration, second virial coefficient, and excess entropy, highlighting the coupling between structure and thermodynamics. Correspondingly, dynamic properties such as diffusivity and viscosity exhibit non-monotonic trends. At interfaces, the wetting behavior of HNP droplets is examined on both smooth and physically patterned surfaces. Increasing segment-surface interaction strength enhances spreading and reduces the equilibrium contact angle. On rough substrates, a transition from Cassie-Baxter-like to Wenzel-like states is observed, governed by the ability of grafted chains to penetrate and conform to surface features. A dimensionless roughness parameter is further introduced to unify surface effects, revealing a nonlinear correlation with contact angle. These findings provide molecular-level insights into how nanoparticle architecture and surface topology control macroscopic properties, offering guidelines for designing functional soft materials with tunable wetting and rheological behavior.