Gels of catanionic vesicles and hydrophobically modified poly(ethylene glycol)

The association between hydrophobically modified polyethylene glycol (HM-PEG) and sodium dodecyl sulphate/didodecyldimethylammonium bromide (SDS/DDAB) catanionic vesicles is studied by rheology, (1)H-NMR, and cryo-TEM techniques. Phase behavior studies were performed as a function of polymer weight fraction and vesicle volume fraction. At sufficiently high polymer weight fraction and/or vesicle volume fraction, a gel phase is detected, indicating the presence of a three-dimensional network. Phase separation was also identified, with a dilute solution coexisting with a bluish precipitate ( gel fraction). Vesicle-polymer binding is expected to occur via the insertion of the polymer hydrophobes into the vesicle bilayer. Each vesicle can act as a cross-linking point in the network structure. The size of the vesicles is found to be important in terms of the storage modulus and viscosity of the polymer-vesicle mixed solutions. On the other hand, changes in the vesicle total net charge do not influence the association and the rheological properties. We also address the question of how the length of the hydrophobic modification can influence the rheology of the system and, as expected, larger hydrophobic groups increase the cross-linking and the relaxation time