Robustness of Classical Nucleation Theory to Chemical Heterogeneity of Crystal Nucleating Substrates

Heterogeneous nucleation is a process wherein extrinsic impurities facilitate crystallization by lowering nucleation barriers and constitutes the dominant mechanism for crystallization in most systems. Classical nucleation theory (cnt) has been remarkably successful in predicting the kinetics of heterogeneous nucleation, even on chemically and topographically nonuniform surfaces, despite its reliance on several restrictive assumptions, such as the idealized spherical-cap geometry of the crystalline nuclei. Here, we employ molecular dynamics simulations and jumpy forward flux sampling to investigate the kinetics and mechanism of heterogeneous crystal nucleation in a model atomic liquid. We examine both a chemically uniform, weakly attractive liquiphilic surface and a checkerboard surface composed of alternating liquiphilic and liquiphobic patches. We find the nucleation rate to retain its canonical temperature dependence predicted by cnt in both systems. Moreover, the contact angles of crystalline nuclei exhibit negligible dependence on the nucleus size and temperature. On the checkerboard surface, nuclei maintain a fixed contact angle through pinning at patch boundaries and vertical growth into the bulk. These findings offer insights into the robustness of cnt in experimental scenarios, where nucleating surfaces often feature active hotspots surrounded by inert or liquiphobic domains.