Structure of solvation shells around colloidal nanoparticles
In a liquid, the arrangement of solvent molecules is determined by their mutual interaction. At an interface, for instance in a pore or around a colloidal particle, the arrangement of solvent molecules changes in comparison to bulk due to the interaction with the surface. Alcohols and water for example build hydrogen bonds to surface species. The restructuring extends about 3-5 molecular layers into the bulk.
We showed that such solvation shells around nanoparticles can be studied with high-energy X-ray diffraction and pair distribution function (PDF) analysis [Science 347 (2015), 292; Nat. Commun. 10 (2019) Art. 995].Copyright: © M. Zobel, R. Neder, S. Kimber
In the figure, the restructuring of ethanol molecules around a nanoparticle decorated with an organic stabilizer and hydroxy groups is depicted. Restructured ethanol molecules exhibit a sinusoidal oscillation of the electron density profile along the surface normal (green curve). From the oscillatory signal, important conclusions about the extent and magnitude of solvent-particle interactions can be drawn. We can also access the internal atomistic and molecular arrangement of the solvent molecules at the interface.
Solvent-nanoparticle interactions are specific for each solvent-nanoparticle pair and dependent on many different factors like particle size, composition, crystallinity, or surface decoration. Therefore, a systematic study of these parameters onto the solvent restructuring around colloidal nanoparticles is crucial.
We investigate solvate and hydrate shells around magnetic and non-magnetic nanoparticles. Because of their magnetic properties, magnetic iron oxides and ferrites are of great interest, for example, for applications in biomedicine and in ferrofluids. Metal oxide nanoparticles of magnetic and non-magnetic nature (Fe3O4, ZnO, TiO2, ...) are often used as catalysts or in nanotechnology, where the interface properties e. g. can determine the catalytic properties.
We use different synthesis routes to fine-tune nanoparticles of different sizes, shapes and we employ various ligands for long-term colloidal stability. With laboratory-based characterization techniques such as XRD, DLS, TGA, IR or CHN analytics, we determine the particle properties. Ultimately, the solvation and hydration phenomena of colloidally stable dispersions are investigated at dedicated beamlines at synchrotron radiation facilities.
In any step from synthesis, characterization with physicochemical techniques as well as for beamtimes, we look forward to train and hire motivated students.
Eckardt, Mirco; Thomae, Sabrina L. J.; Dulle, Martin; Hörner, Gerald; Weber, Birgit; Förster, Stephan; Zobel, Mirijam*: Long-term colloidally stable dispersions of 5 nm sized mixed metal ferrites.
ChemistryOpen (2020), 9, 1214–1220; https://doi.org/10.1002/open.202000313
Thomä, L. J. Sabrina; Krauss, Sebastian W.; Eckardt, Mirco; Chater, Phil; Zobel, Mirijam*: Atomic insight into hydration shells around facetted nanoparticles.
Nature Communications vol. 10 (2019) issue 1, https://doi.org/10.1038/s41467-019-09007-1
Zobel, Mirijam*; Neder, Reinhard B.; Kimber, Simon A. J.*: Universal solvent restructuring induced by colloidal nanoparticles.
Science vol. 347 (2015) issue 6219. - pp. 292-294; https://doi.org/10.1126/science.1261412
Zobel, Mirijam: Observing structural reorientations at solvent-nanoparticle interfaces by X-ray diffraction - putting water in the spotlight.
Acta Cryst. A72 (2016), 621-631; https://doi.org/10.1107/S2053273316013516
Deutsche Forschungsgemeinschaft (DFG)
Grant Nr.: SFB 840, Project C7
Title of project: Local order of solvent molecules at solid-liquid interfaces in colloidal dispersions
Project period: until September 2021