NSF Materials World Network: Heterogeneous Nucleation on Nanoporous Substrates

The proposed research effort will support an international collaboration between the Chayen group at Imperial College, London (IC), specializing in protein crystallization and the Erlebacher group at Johns Hopkins University, Baltimore (JHU), which specializes in the synthesis and surface modification of nanoporous metals. By marrying these specializations, a fundamental study of heterogeneous crystal nucleation on nanoporous substrates will be efficiently pursued. The collaboration is structured with significant exchange of students and junior personnel; ultimately, the JHU team will develop in-house skills in solution-phase crystallization, and the IC group will learn materials synthesis techniques for fabricating nanoporous metals and nanoporous metal composites, leading to advances in crystallization generally. Fundamentally, our proposed research considers a new approach to thinking about the heterogeneous nucleation of macromolecular species. In traditional heterogeneous nucleation theory, nucleation rates are controlled by the relative interfacial energies between the solvent, substrate, and nucleus. Here, we will tailor the substrate to expose not just one uniform surface to the solution, but instead to expose a statistically relevant distribution of three-dimensionally oriented nucleation sites. Modifications of nucleation theory to explore this idea is an important part of the proposed work and is required for applying the technique generally.A detailed study of the nucleation rate of macromolecules over porous substrates will be performed using a new substrate material / nanoporous gold Nanoporous gold is a random, uniform, mesoporous material whose mean pore size can be varied from 3-50 nm using simple chemistry. Its surface is also easily chemically modified, and all these features together make it uniquely perfect for this kind of study.The results of this research will yield new understanding of the fundamentals of heterogeneous nucleation, with general applicability to protein and colloidal crystallization. Furthermore, the international collaboration will help to build international networks in nucleation theory and experiment, bridging the disciplines of thin film metallurgy and solution phase crystallization.