Interactions between catanionic vesicles and oppositely charged poly electrolytes-phase behavior and phase structure

Structural and phase behavior effects resulting from the addition of a poly electrolyte to a solution of oppositely charged vesicles are investigated i n this work. Two cationic polyelectrolytes derived from hydroxyethylcellulo se were used: JR400, a homopolymer, and Quatrisoft LM200, a polymer modifie d with alkyl side chains. The vesicles are composed of mixed anionic surfac tant (sodium dodecyl sulfate) and cationic surfactant (didodecyldimethylamm onium bromide), bearing 29 mol % of the caf;ionic amphiphile. The phase beh avior for the two mixed polymer-surfactant systems was investigated for pol ymer concentrations between 0.001 and 3 wt%. Three main regions were found in the two-phase maps, upon polymer addition: (i) a bluish solution phase; (ii) a wide region of phase separation, containing a precipitate and a solu tion; and (iii) a polymer-rich gel region, forming upon charge reversal of the system. Cryo-TEM imaging of the solution phase shows the formation of f aceted vesicles and disklike aggregates, upon addition of JR400. Fbr the LM 200 system, besides the formation of faceted vesicles, clusters of vesicles and other bilayer structures are imaged. In the polymer-rich phase of JR40 0, membrane fragments, disklike aggregates, and vesicles are also found. Th ese bilayer aggregates are likely to be involved with the polymer in highly connected networks, giving rise to the observed bluish gels. Electrostatic interactions, reinforced by hydrophobic interactions in the case of LM200, are the main driving force for the structural transitions observed.