Solvent restructuring at colloidal interfaces
In many everyday applications, nanoparticles can be found in a dispersed state, i.e. in sun lotions or as drug vehicles. Nanoparticles also leak from those products into our environment, where they interact with water.
In bulk solvents, the interactions between the solvent molecules determine their mutual arrangement. At interfaces, in pores and around colloidal particles, the bulk solvent structure changes due to interactions between the solvent molecules and the surface. Depending on the particle and solvent properties, bonds between the surface and the solvent are formed and typical restructuring phenomena of liquids extend over ca. 3 to 5 layers of solvent molecules away from the surface before the bulk structure is regained. Just recently, we could demonstrate that even tiniest nanoparticles possess solvation shells in water, alcohols and hexane. The figure shows the restructuring of ethanol molecules around a nanoparticle with organic ligand and hydroxyl groups. The restructured solvent molecules result in a sinusoidal oscillation of the electron density profile along the surface normal (green curve), which we can detect in high-energy X-ray scattering experiments. Restructuring phenomena of solvent molecules at nanoscopic and mesoscopic interfaces are a current research topic, since those interfaces just recently became accessible thanks to improvements in X-ray sources and detectors.
Now, we want to study in detail, how different particle properties (size, shape, crystallinity, surface groups, …) impact the solvent restructuring. In particular, particles with biomedical applications, i.e. nanoparticle-enzyme complexes or magnetic particles for drug targeting, are of interest.
Fur this purpose, we synthesis magnetic iron oxide nanoparticles of various diameters (6 - 15 nm) with a large variety of small organic surface groups.
Thomä, S. L. J., Krauss, S. W., Eckardt, M., Chater, P., Zobel, M., Atomic insight into hydration shells around facetted nanoparticles, Nature Communications (2019)10:995, DOI: 10.1038/s41467-019-09007-1.
Zobel, M., Neder, R. B., Kimber, S. A. J., Universal solvent restructuring induced by colloidal nanoparticles, Science 347 (2015), 6219, 292-294.
Zobel, M., Observing structural reorientations at solvent-nanoparticle interfaces by X-ray diffraction - putting water in the spotlight, Acta Cryst. A72 (2016), 621-631