Effects of crystalline/non-crystalline emulsifiers on foamed emulsion: Microstructure, rheological properties, and 3D printing

Abstract

In this paper, glycerol monostearate and fumed silica were used as the crystalline and non-crystalline emulsifier, respectively, to stabilize the oil-water interface together with polyglycerol polyricinoleate. Lacquer wax structured the oil phase as a gelling agent. Then, foamed emulsions were prepared by whipping. For crystalline emulsifier, a mass of wax crystallized on the oil-water interface due to the templating effect that promoted the heterogeneous nucleation. Droplets wrapped with “crystalline shell” could connect to matrix and contribute to system strength as active fillers. Therefore, the modulus of foamed emulsions increased with the water content correspondingly. Similarly, droplets with “crystalline shell” could connect to the wax that absorbed at the oil-air interface and aggregate around the bubble, which could be observed with microscopy. Whereas, the crystal was hardly observed at the oil-water interface stabilized by non-crystalline emulsifiers. The droplets simply filled in the bulk oil phase, and foamed emulsions with different water content had approximate modulus. To further convince the conclusion above, overrun and 3D printing were conducted. The overrun rates of crystalline emulsifier-based foamed emulsion were lower than that of non-crystalline emulsifier at higher water content (W:O=30:70, 50:50 w/w). It might due to the templating effect, which reduced the mass of crystal in bulk phase that could stabilize bubbles during whipping as the Pickering particle. In case of crystalline emulsifiers-based foamed emulsions, the modulus and height of the printed sample increased with the increasing water content, while there was no significant tendency for non-crystalline emulsifiers-based foamed emulsions.