FAU researchers show how liquids change at the surfaces of nanoparticles
They have become part of our daily lives almost without us noticing – nanoparticles are responsible for unique properties in cosmetics, food and medication, but also in catalysts. In most of their applications nanoparticles are dissolved in liquids as many of their properties occur at their surfaces. However, until recently researchers were only able to use theoretical modelling to show whether and how the internal structure of a liquid changes at the surface of a nanoparticle. Physicists at FAU have now been able to prove this in an experiment for the first time. Their findings have recently been published in the renowned journal Science.*
Liquids such as water and alcohol have an internal structure. Oxygen atoms react with hydrogen atoms, forming structures such as rings or chains within the liquid. This structure breaks up around smooth surfaces, such as vessel walls. Researchers predicted that liquids would behave similarly around nanoparticles, but they did not have any experimental proof. FAU researchers Prof. Dr. Reinhard Neder and Mirijam Zobel (Professorship of General Mineralogy/Crystallography) have now provided this proof.
To do so they used the pair distribution function (PDF). As there are only a few devices in the world able to carry out the precise PDF measurements, the FAU researchers travelled to the European Synchroton Radiation Facility in Grenoble, France. There they exposed samples – a range of nanoparticles that they had purchased or made themselves, such as zinc oxide or silver, dissolved in various solvents – to high-energy X-rays. The radiation produced an X-ray image as soon as it touched the electrons in the nanoparticles and in the solvent. Using these images the researchers calculated how far away the individual atoms were from one another, allowing them to show that the molecules reordered themselves at the surfaces of the nanoparticles and the liquid. This reordering is strongest directly at the surface and affects around five layers of molecules until the usual property of the liquid is resumed further away from the surface. ‘We expect that our general results will have a significant effect on the modelling of chemical reactions at surfaces,’ explains Mirijam Zobel.
*M. Zobel, R. B. Neder, S. A. J. Kimber, Science, 16. January 2015, Vol. 347, #6219. DOI: 10.1126/science.1261412
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