Interfacial behavior of cyclodextrins at the oil-water interface of Pickering emulsion

An oil-in-water (O/W) Pickering emulsion stabilized by cyclodextrins (CDs), including α-, β-, γ-CD, and the hydroxypropyl (HP) derivatives, was prepared by high-speed homogenization. The interfacial behavior of CDs was studied by the contact angle, surface tension, interface tension, and adsorption kinetics. The physicochemical properties of CD Pickering emulsion were characterized by adsorption content, microstructure, rheology, and instability index. The results showed that the contact angles (85.30° and 75.93°), diffusion rates (−0.2481 and −0.1285), and adsorption rates (−0.0045 and −0.0028) of α-CD and β-CD were significantly higher than those of HP-CD derivatives, and emulsions possessed smaller droplet size (both about 7.5 μm) and better stability compared with HP-CDs derivatives. The formation of Pickering emulsion was attributable to the interfacial adsorption layer structure at the oil-water interface formed by the self-assembly of CD. Subsequent studies on the physiochemical properties of emulsion showed that Pickering emulsions stabilized by α-CD and β-CD had better storage modulus, loss modulus, viscosity, storage stability, and centrifugal stability. HP-α-CD, HP-β-CD, and HP-γ-CD stabilized emulsions delaminated and sedimented within a short time. The amorphous HP-α-CD, HP-β-CD, and HP-γ-CD were difficult to form stable interfacial layers and adsorb on the surface of oil droplets due to their high-water solubility and poor crystallinity.