Aggregation behavior of poly(ethylene glycol) chain-containing anionic amphiphiles: Thermodynamic, spectroscopic and...

Two novel amphiphilic molecules were synthesized by the reaction between poly(ethylene glycol) methyl ether (mPEG) of different chain lengths and sodium-2-mercapto ethane sulfonate (mesna). Different techniques, such as surface tensiometry, conductometry, fluorescence spectroscopy, dynamic light scattering, UV-vis spectroscopy, transmission electron microscopy, and isothermal titration calorimetry were employed to investigate the self-assembly properties of the PEG-based single-tailed amphiphiles in aqueous buffer. Despite having so called polar tail the amphiphiles exhibit aggregate formation in aqueous buffer as well as in water. The shorter chain amphiphile was shown to form bilayer vesicles in contrast to small micelles by its longer chain counterpart. The helicity of the PEG chain was taken into consideration to interpret the difference in self-assembled microstructure formation. The thermodynamics of the self-assemblies were also thoroughly examined. The thermodynamic parameters clearly suggested that the hydrophobic interaction among the PEG chains is the main driving force for aggregate formation. The self-assembled microstructures were observed to be fairly stable with respect to increase of surfactant concentration, aging time and temperature.