Influence of the particle type on the rheological behavior of Pickering emulsions

In order to get a better understanding of potential relationships among the microstructure and stability of Pickering emulsions, theological studies were performed using differently modified disperable colloidal Boehmite alumina nanoparticles. Hysteresis loop measurements and dynamic (oscillatory) rheological measurements on two different emulsion systems were carried out in linear and non-linear regime at different storage time. Differential scanning calorimetry (DSC) results, transmission electron microscopy (TEM) and optical microscopy images of these emulsion systems were additionally analysed in respect to reveal the emulsions type and their microstructure. Pickering emulsion stabilized by moderately hydrophobic particles exhibited inhomogeneous structure, relative large yield stresses and thixotropic flow behavior, indicating a formation of a three-dimensional network. Emulsion stabilized by rather hydrophobic particles with a contact angle around 90, was revealed to be an oil-in-water-in-oil multiple emulsion. The emulsion was homogenous and showed thixotropy, indicating the presence of a three-dimensional network. However, a phase separation slightly occurred in the storage time evaluated meaning that the stability of this emulsion need be improved. (C) 2011 Elsevier B.V. All rights reserved.