Professor Netz gets this award for his ground-breaking scientific discoveries that answer many core questions relevant to colloid and interface science by using a variety of theoretical methods, but always in close connection with experimental results. His pioneering achievements, which include strong-coupling theory for counter-ion attraction, molecular mechanisms of hydration repulsion and a predictive Hofmeister theory, solve fundamental core riddles where classical continuum theory failed. His universal physical principles have a genuine textbook character and profoundly shape the mechanistic understanding of our field:
1. Attractive interactions between similarly charged objects, such as DNA or charged colloids in di- or trivalent ion solutions, have been observed experimentally for a long time, although standard Poisson-Boltzmann theory strictly predicts repulsion between similarly charged surfaces. Using field-theoretic methods, Netz derived a strong coupling theory for charged systems, which predicts attraction between similarly charged bodies when the counterion valency is sufficiently high. This theory also allows for a simple interpretation in terms of electrostatic bridging attraction due to discrete counterions.
2. Netz and his group demonstrated that the impact of different ions on the interaction between two surfaces depends on both surface polarity and charge, as well as slight variations in ion-surface propensities. This explains the Hofmeister series reversal observed for different proteins and colloidal surfaces. This work paved the way for a quantitative explanation of ion-specific effects on complex surfaces in typical biological and colloidal applications, as well as the coupling between bulk and surface ion-specific effects.
3. The Netz group demonstrated through atomistic simulations of different surfaces that the dielectric constant and viscosity of water differ from their bulk values close to hydrophilic and hydrophobic surfaces. The experimentally well-established apparent excess surface conductivity follows from the combined effects of interfacial dielectric and viscosity properties, eliminating the need for additional assumptions. The theory developed by Netz and his colleagues thus simultaneously explains published sets of capacitance, electrokinetic and surface conductivity data on hydrophilic and hydrophobic surfaces with striking accuracy, and has since been successfully applied to a wide range of surfaces.
4. The molecular mechanism of hydration repulsion remains unclear, particularly since molecular dynamics simulations at constant water chemical potential have proven challenging. However, the Netz group introduced novel simulation methods by which they were able to extract the forces between lipid bilayers from atomistic simulations that were in quantitative agreement with experiments.
5. Air bubbles are known to be able to act as if they are negatively charged, typically due to hydroxide adsorption. Two other anomalies have been observed in this context: the Jones– Ray effect, which describes a universal surface tension minimum in salt solutions at millimolar concentrations, and the stability of wetting films on negatively charged surfaces. The Netz group demonstrated that these three phenomena are connected and can be modelled and explained quantitatively by assuming the presence of negatively charged surfactants at nanomolar concentrations in the laboratory water used.
In addition to his brilliant intellect and deep understanding of many areas of colloidal science, one of Netz’s outstanding characteristics as a researcher is his ability to choose whichever method is needed to tackle a given problem, whether numerical, analytical or a combination of both. This is due to his strong theoretical and mathematical background, as well as his interest in numerical techniques. During his long career, he has also fostered and mentored many bright young scientists to become independent, brilliant researchers.