Date(s) - 10/06/2020
3:00 pm - 4:00 pm
Jim De Yoreo, Ph.D.
Chief Scientist for Materials Science in the Physical and Computational Sciences Directorate
Pacific Northwest National Laboratory (PNNL}
The emergence of order in materials systems ranging from simple salts to complex supramolecular arrays has long been viewed through the lens of classical nucleation theory in which monomeric building blocks assemble into ordered structures through inherent thermal fluctuations that overcome a free energy barrier. However, 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.
Macromolecular systems exhibit particularly rich assembly dynamics due to their conformational flexibility and interactions that span many length scales. Despite the complexity of these pathways, a holistic framework for understanding them based on classical concepts emerges when one considers perturbations in the free energy landscape from a smoothly varying surface to one rich in minima and maxima, as well as dynamical factors that drive hierarchical pathways due to kinetic constraints.
I illustrate that framework using in situ TEM and AFM studies of inorganic, organic, and macromolecular systems, which provide a molecular-scale view of assembly pathways and dynamics. In particular, the results highlight the key role of interfaces in creating heterogenous distributions of water and ions, which create low barrier pathways to ordering. The findings provide a common basis for understanding the development of order in diverse systems.