Back to Table of Contents

44193-AC7
Equilibrium and Dynamic Properties of a Photosensitive Surfactant System

Nicholas L. Abbott, University of Wisconsin (Madison)

The goal of our research is to develop a fundamental understanding of the equilibrium phase behavior and dynamics of an aqueous mixed surfactant system containing a light-sensitive surfactant.  Because bulk and interfacial properties of the surfactant system can be reversibly tuned as well as spatially patterned by illumination with different wavelengths of light, this type of aqueous surfactant system has the potential to be broadly useful as a “tunable solvent” in a number of contexts, including novel separations and analytical methods.  
Over the past year, we have devoted effort to an investigation of the thickness of vesicles formed by mixtures of light sensitive surfactants and anionic surfactants. Past studies have established that the thickness of a vesicle bilayer formed from a mixture of conventional anionic and cationic surfactants is determined by a delicate balance of factors, including electrostatic interactions, van der Waals forces, and chain packing constraints.  This complex balance of factors means that the bilayer thickness is not easily predicted from knowledge of the structure of conventional surfactants.  In our study, we synthesized a family of rigid, bolaform surfactants with the structure bis(trimethylammoniumalkyloxy)azobenzene dibromide, where the alkyl group was butyl, hexyl, or octyl.  We used small angle neutron scattering and quasi-elastic light scattering to characterize the microstructures formed when the cationic bolaform surfactants were mixed with either sodium dodecylsulfate or sodium tetradecylsulfate in aqueous solutions.  Small angle neutron scattering spectra interpreted using form factor fits indicate that the three rigid, bolaform surfactants span the bilayers of vesicles formed by these surfactants mixtures, thus constraining the bilayer thicknesses to the end-to-end lengths of the bolaform surfactants.  We conclude that use of rigid, bolaform surfactants provides a simple means to design vesicles from anionic and cationic surfactants that form spontaneously and have predictable bilayer thicknesses.  These results suggest some simple rules that enable the rational design of surfactant-based and photosensitive nanostructures.
 

Back to top