Interfacial rheology as a tool to study the potential of cyclodextrin polymers to stabilize oil–water interfaces

Abstract

The aim of this work is to characterize rheologically the interfacial properties of oil/water interfaces stabilized with β-cyclodextrin (CD)-based inclusion complexes. Interfacial experiments were conducted using two different hydrophobic oils: Parsol MCX and Squalene. Dilatational interfacial rheology was performed with a dynamic drop tensiometer, allowing the determination of the interfacial tension from the drop profile, and the calculation of rheological values (phase angle, elastic and viscous moduli) from the correlation between the drop area and the interfacial tension sinusoidal variations. Practically, an oil drop was formed in the aqueous phase containing the CD-derivative. With Parsol MCX, no correlation was observed, indicating that surfactants were not adsorbed at the interface. With Squalene, two β-CD-derivatives were used: monomers and polymers. With monomers, a solid membrane was created, impeding any rheological measurements. This is consistent with the crystallization of the system and the impossibility to formulate an emulsion with monomers. With polymers, an effective correlation of the drop area with the interfacial tension variation demonstrated the adsorption of the CD-complex at the interface. Rheological values clearly indicated the formation of an elastic interface, preventing droplets coalescence: an emulsion formulated with β-CD polymers results in a better stabilization.