Phase behaviour, microstructure and ibuprofen solubilization capacity of pseudo-ternary nonionic microemulsions

Abstract

This study investigated phase behaviour, microstructure and solubilization capacity of pseudo-ternary surfactant/cosurfactant/isopropyl myristate/water systems employing complex mixtures of nonionic surfactants for formation of single-phase microemulsions. The surfactant was PEG-8 caprylic/capric glycerides (Labrasol (R)). A well defined mixture of octoxynol-12 and polysorbate 20 and/or PEG-40 hydrogenated castor oil, available as commercial nonionicsurfactants Solubilisant gamma (R) 2421, Solubilisant gamma (R) 2429 and Cremophor (R) RH 40, respectively, were evaluated as cosurfactants. Surfactant + cosurfactant mixtures were treated as a single component (pseudo-component), since a surfactant-to-cosurfactant weight ratio (Km 50:50) was constant through the study. Phase behaviour study revealed enlargement of single-phase microemulsion area as surfactant + cosurfactant-to-oil weight ratio (SCoS/O) increases. The formation of fully dilutable microemulsions containing the maximum of water incorporation in the surfactant/cosurfactant/oil preconcentrates of W(max) >= 80% w/w, was achieved at SCoS/O 90:10. Microemulsions formed along the single-phase sequence at SCoS/O 90:10 in the presence of different cosurfactants, were characterized using polarized light microscopy, photon correlation spectroscopy (PCS), and rheological measurements. Different performances of complex mixtures of nonionic surfactants in stabilization of single-phase microemulsions were observed only in highly diluted oil-in-water microemulsions area. Investigation of solubilization capacity for poorly soluble drug ibuprofen revealed the critical importance of water-to-surfactant + cosurfactant ratio and penetration of oil at the interface.