In situ studies of hierarchical nucleation pathways in silicate and carbonate systems

Nucleation is the seminal process in the formation of ordered structures ranging from simple inorganic crystals to macromolecular membranes. Recent observations have revealed a rich set of hierarchical pathways involving higher-order species ranging from multi-ion clusters to dense liquid droplets to transient amorphous or crystalline phases. These pathways create long-lived metastable species that can both alter the evolution of natural geochemical reservoirs through their interactions with other components in the system and offer an opportunity to capture non-equilibrium states with novel properties. However, understanding in what systems these hierarchical pathways exist and why is an outstanding challenge. To investigate the dynamics of hierarchical nucleation pathways and determine the underlying mechanisms that lead to their emergence, we have applied in situ TEM, AFM and NMR to a diverse set of inorganic and macromolecular systems and interpreted the results with the help of molecular simulations. In this presentation, I focus on two systems with relevance to geochemical and biological systems. The first is calcium carbonate, which constitutes the largest terrestrial reservoir of CO2 and records the interaction of earth and biota through time back to the Cambrian. Here I focus on crystallization via a dense liquid phase (DLP) precursor, as well as the role of poly-amino acids and proteins in stabilizing the DLP and directing the formation of calcite, as well as its subsequent crystal growth by assembly of primary particles with non-natural faces. The second is a family of highly hydrated silicate framework crystals that provide insights into the role of oligomerization during the early stages of formation in zeolites and other polymeric silicates. In this case, the investigations focus on the importance of muti-ion oligomeric building units in defining the timing, mechanism, and dynamics of nucleation, as well as the pathway of subsequent crystal growth. Together, these two lines of research help to fill in the gaps in understanding of hierarchical nucleation pathways.

Zoom link: https://dipc-org.zoom.us/j/96589502463