Reinhard Strey (Köln)
Prof. Reinhard Strey is a researcher who has significantly shaped the field of surfactant science. Among his numerous scientific achievements, the most salient are certainly his contributions to our enhanced understanding of microemulsions. Prof. Strey’s meticulous and comprehensive investigations allowed proving or disproving existing theoretical considerations by using most advanced experimental techniques. With this approach he deduced conclusive evidencethat allowed understanding the phase behavior and structure of microemulsions and relating them to the molecular structure of surfactant molecules and oils involved. This is certainly his most prominent accomplishment but he also contributed substantially to various other fields of colloid science.
His accomplishments started with a very thorough and systematic investigation of phase behavior and structure of microemulsions formed by nonionic surfactants, where he ingeniously used scattering techniques and electron microscopy to elucidate the structural evolution of the microemulsions as a function of composition and temperature. These landmark studies largely contributed to our current understanding of microemulsions, i. e. how they are related to the interfacial tensions of the systems and how all these properties arise from the bending energy of the amphiphilic monolayers that separate the oily and aqueous domains within the microemulsions.
In cooperation with Prof. Sam Safran of the Weizmann Institute he then generated a deeper theoretical insight into how the interplay between curvature energy and entropy controls the structural transition from individual microemulsion droplets to a bicontinuous structure. This theoretical approach allowed relating the changes of the microstructure to the ultralow interfacial tensions and wetting properties of the microemulsions.
Another major contribution to the development of microemulsions was the observation of the boosting effect, where the addition of amphiphilic copolymers can enhance enormously the solubilization capacity and the structural size of microemulsions. This effect was studied in thorough detail. The structure and dynamics of these copolymer modified microemulsions could be explained consistently by the changes of the bending rigidity of the amphiphilic film that arise from the presence of the copolymers.
In more recent years Prof. Strey then extended the scope of his concepts, which were initially developed and demonstrated on simple alkanes, to more challenging hydrophobic compounds like triacylglycerol and CO2. Using his insights into the basic foundations of solubilization, he was able to devise strategies for effective solubilization by microemulsions that contain very hydrophobic compounds where microemulsification with water has not been easy to obtain.
At the same time, he ventured successfully into the really interesting practical application of formulating microemulsions with diesel in order to obtain fuels that are not only more energy efficient than normal carburants but also much lower in producing toxic exhaust fumes. Furthermore, Prof. Strey combined his in-depth knowledge in the field of microemulsions with his second passion, nucleation, to produce nanofoams, which are of great interest for many applications such as thermal insulation, membranes and sound absorption. He invented the principle of supercritical microemulsion expansion, in which micelles are swollen with supercritical propellants such as CO2 or ethane and these microemulsions are then expanded and fixed by simultaneous polymerization.
Prof. Strey is also the inventor of the NanoFoam by Continuity Inversion of Dispersion process, a further development of which allows the production of PMMA nanofoams with an adjustable pore size of 50 nm, a thermal conductivity of less than 23 mW/mK and a surface area of 100 m2/cm3, which are now commercially available through the company SUMTEQ GmbH, which he founded with two PhD students in 2014. This was the demonstration of how insights obtained in fundamental research can become successfully transferred into practical applications of general importance.
Certainly, Prof. Strey is an inspiring scientist who has been pioneering our understanding of solubilization by surfactants and formation of microemulsions. His cleverly designed experiments combined with a deep theoretical understanding of the underlying physical principles allowed him to give us the comprehensive knowledge of microemulsion properties and how to control them on a molecular level.