Salt-responsive monoolein cubic phase containing polyethyleneimine gel

Monoolein (MO) cubic phases responsive to salt ions were prepared by immobilizing polyethyleneimine (PEI) in its water channel through its electrostatic attraction with octanoic acid (OA) intercalated in MO bilayer and ionically gelling PEI using tripolyphosphoric acid (TPPA). The interfacial tension of PEI/OA solution markedly decreased with increasing concentration and it was typical of the interfacial tension profile of a surfactant solution. TPPA remarkably lowered the transition temperature of MO cubic phase from about 63 °C to below 46 °C, possibly because the hydroxyl groups of TPPA participated in hydrogen bonding with the glycerol residue of MO. The cubic phases showed finger print–like patterns on TEM micrographs and neither OA, nor PEI, nor TPPA affected the structure of the cubic phases. When PBS was used as a release medium, the release degree of a dye (i.e. Rhodamine B) loaded in the cubic phase was more than two times higher than that obtained using distilled water. The salt ions contained in the buffer solution would be able to dissolve PEI gel via ion exchange and promote the release of dye out of the cubic phase.