In-situ AFM is a powerful tool for understanding mineral precipitation processes, thanks to its unique ability to provide time-resolved, real-space imaging of mineral-water interfaces with sub-nanometer resolution. When applying AFM to a variety of systems, ranging from two-dimensional protein films to inorganic salts and oxyhydroxide minerals, we observe a wide diversity of nucleation behavior. In many circumstances, we observe prototypical classical nucleation behavior, wherein the formation of a critically sized nucleus allows 2D islands to form and propagate across a surface. However, subtle differences in parameters such as surface tension and epitaxial strain can result in drastically different growth outcomes. For example, the interplay of surface tensions may allow monolayer films to grow at conditions well below the threshold needed to nucleate a bulk phase; while interfacial strain may inhibit the growth of multilayers even well above the threshold needed to grow a bulk phase. Some of the most interesting cases involve surface charging, for which charge balance constraints associated with the electrical double layer can drastically change the energy landscape for nucleation and growth. For example, when positively charged aluminum hydroxide films grow atop a negative charged mica substrate, our work indicates that surface charging can stabilize a nanostructured surface mesophase, in which regions of positive and negative charge are intrinsically intermixed to obtain local charge balance. Cases like this may allow precipitation to occur within a one-phase region of the phase diagram, thus bypassing the need to form classical critically sized nuclei.

Imaging heteroepitaxial nucleation at the mineral-water interface with in-situ AFM: New insights on the influence of surface tension, epitaxial strain, and surface charging.

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.