Microstructure and rheology of oleogel-stabilized water-in-oil emulsions containing crystal-stabilized droplets as active fillers

Abstract

Rice bran wax (RBX) oleogels were used to kinetically stabilize water-in-oil (W/O) emulsions containing up to 25 wt% water dispersed as micron-size droplets using glycerol monostearate (GMS) as the surfactant. The combined presence of GMS and RBX resulted in emulsions stable against coalescence and phase separation. The inclusion of a dispersed aqueous phase had a considerable effect on viscoelastic behaviour, with storage modulus increasing from ∼200 Pa in the emulsion containing a 7.5 wt% aqueous phase to ∼16,000 Pa with a 25 wt% aqueous phase. Light microscopy revealed that RBX crystals were predominantly located in the continuous phase, with GMS crystals present as crystalline shells englobing the dispersed aqueous droplets. The presence of an aqueous phase within the oleogel enhanced storage modulus more so than expected by increasing solid phase content alone, particularly at higher water loads. This strongly suggested that interactions between continuous phase RBX crystals and interfacially-bound GMS solid shells resulted in the dispersed aqueous phase acting as an active filler. Overall, this study demonstrated that the rheology of W/O emulsions may be tailored through oleogelation, particularly if the dispersed droplets are stabilized by interfacial crystalline shells that directly interact with the continuous phase gel network.