The impact of alkanes on the structure of Triton X100 micelles

Here we investigate the structural evolution of TX100 micelles upon loading with several linear and cyclic alkanes by DLS, PGSE-NMR, 2D NOESY NMR, viscosity measurements, and molecular dynamic simulations. Our results confirm that TX100 alone forms spherical, onion-like micelles made of several partially interpenetrating surfactant layers where the polyethylene glycol chains are in contact with the tetramethyl-butyl-phenyl moieties. Loading with non-penetrating oils larger than decane induces a decrease in micellar size and hydration because the alkane molecules compete with both water and tetramethyl-butyl-phenyl groups for the polyethylene glycol chains. This results in the partial peeling of the “onion” and in the dehydration of polyethylene glycol chains so that the micelles increase in number and decrease in size upon alkane loading. In contrast, small and penetrable oils (mainly cyclo-alkanes) first swell the onion-like micelles (inducing an increase in size) and only above a critical oil/surfactant ratio does the oil induce the weakening of the multilayer structure and the dehydration of polyethylene glycol chains found in long linear alkanes.