Professor Michael Gradzielski, Stranski Laboratory for Physical Chemistry / Molecular Material Sciences, Department of Chemistry, Technical University Berlin, Germany

Vesicle Gels – Rheological Control and Solubilization

Amphiphilic molecules can self-assemble in the form of bilayers, as for instance they do in the case of phospholipids that form biological membranes. If such bilayers form closed spherical objects they are called vesicles or liposomes, that can vary quite a bit with respect to their size and detailed structure. Due to their similarity to biological membranes vesicles are not only of fundamental interest but also frequently employed in formulations from pharmacy, cosmetics, detergency etc., and for instance are interesting as drug delivery systems. Densely packed vesicles form vesicle gels that allow for substantial control of rheological properties with only relatively small amounts of amphiphile required, which is also interesting for many applications. In vesicle gels based on nonionic surfactants on 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 50-500 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 of high oil content. In general such lamellar systems “doped” with small amounts of ionic surfactant are very versatile and interesting systems with respect to their solubilization properties and also with respect to their macroscopic properties and can be compared to conventional formulations of cosmetic gels.  

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Host: Professor Jan Skov Pedersen, iNANO & Department of Chemistry, Aarhus University