Event
Special ChBE Seminar: Michael Gradzielski
Wednesday, June 18, 2014
2:00 p.m.-3:00 p.m.
Room 2108, Chemical and Nuclear Engineering Bldg.
Professor Srinivasa Raghavan
sraghava@umd.edu
Vesicles – Control of the Formation Process and Solubilization in Vesicle Gels
Michael Gradzielski
Stranski Laboratorium für Physikalische und Theoretische Chemie
Institut für Chemie, Technische Universität Berlin,Germany
Unilamellar vesicles are interesting self-assembled aggregates that may form spontaneously when mixing cationic or zwitterionic with anionic surfactants. In our experiments, the fast formation process was studied by coupling the stopped-flow technique to high-flux SANS/SAXS instruments, allowing to obtain detailed structural information with a time resolution of 5-50 ms. This was done on a model system composed of perfluorinated anionic and zwitterionic hydrocarbon surfactant, showing that it proceeds via a disk-like intermediate state, yielding very monodisperse unilamellar vesicles. However, these vesicles age rather quickly afterwards. Based on detailed knowledge of the formation process it was possible to manipulate it by admixing amphiphilic copolymers. This leads to larger and very monodisperse vesicles, which now in addition are long-time stable. Accordingly by this shaping approach one can obtain unilamellar vesicles with tunable radii in the range of 20-70 nm and with polydispersity indices of 0.04-0.06, which are attractive for a number of applications.
Similarly interesting are densely packed vesicles that form vesicle gels and thereby allow for control of rheological properties. In vesicle gels based on nonionic surfactants, one can control the rheological properties by admixture of rather small amounts of added ionic surfactant, where the absolute rheological moduli also scale with the total concentration and are in the range of 50 to 500 Pa with a yield stress of 1-20 Pa. Such vesicle gels can solubilize rather large amounts of oils (more than 3 times the amount of contained surfactant), where the amount depends in general on the polarity of the oil and can be controlled again by the content of admixed ionic surfactant. These oil-swollen vesicle gels were characterized by means of static and dynamic light scattering, SANS, electric conductivity and electron microscopy. These results show that first the surfactant bilayers swell with increasing oil content before being transformed into a bicontinuous structure.
About the Speaker
Prof. Michael Gradzielski is a Professor of Physical Chemistry and the Dean of the Faculty at the Technical University of Berlin. He is a world-renowned authority on colloids and soft matter, especially those based on surfactants and amphiphilic polymers. Prof. Gradzielski received his Ph.D. in 1992 at the University of Bayreuth working with Prof. Heinz Hoffmann. He has been a full professor at TU Berlin since 2004. He has authored more than 170 scientific publications and in 2009, he received the Liesegang Prize of the German Colloid Society for his research contributions.
