Pickering emulsions stabilized by novel clay–hydrophobin synergism

Abstract

We have studied the physico-chemical properties of high internal oil in water (o/w) emulsions, stabilized by synergistic interaction between hydrophobin and clay. As an emulsifying agent with biological background we used H Star Protein® B (HPB). Its emulsifying partner, Laponite XLG, is a synthetic layered silicate. One to one aqueous mixtures of HPB and Laponite XLG resulted in homogeneous emulsions with an oil mass fraction Φ of 0.65 PDMS. When used separately, both systems form unstable o/w emulsions. Moreover rheological measurements indicate the weak gel-like properties of their emulsions, whereas the simultaneous use of clay and hydrophobin results in long-term stable o/w emulsions with very pronounced gel-like properties. Characteristic rheological properties are their high storage modulus G′ (>1000 Pa), a high yield stress value and viscosity (1 Pa s at a shear rate γ = 100 s−1). Despite a low polydispersity, a certain ripening of the emulsion matrix depending on the incubation time and shear rate was observed. It is concluded that the high storage moduli in the gel-like emulsions are due to the elasticity of the clay–protein films surrounding the oil droplets forming a self-supporting three-dimensional network. Our results highlight the relevance of the novel hydrophobin–clay synergism, resulting in excellently stabilized surfactant-free emulsions.