Stability of multiple emulsions under shear stress

Abstract

Multiple liquid emulsions of the water in oil in water (W1/O/W2) type are used in a variety of consumer or technical applications, for instance in the encapsulation of certain active ingredients. The encapsulation process and release mechanisms of the inner phase of the carrier drops are important in order to properly process and formulate such liquid‐liquid systems. In this work the stability and breakage of multiple W1/O/W2 emulsions under mechanical shear stress are investigated for emulsions with different surfactants and surfactant concentrations of the internal emulsion. Stressing the emulsions in a mechanical stirring process is compared to the membrane emulsification process. The membrane emulsification process results in higher encapsulation efficiencies than the stirring process. The emulsion droplets were subjected to shear stress below and above the critical capillary number for drop breakup. The results show that stable inner emulsions with sufficient surfactant concentrations increase the overall encapsulation efficiency for multiple emulsions subjected to shear stress, although the effect is not prominent. The depletion of the carrier oil droplets could be achieved for Ca numbers below the critical limit, reducing the encapsulation efficiency below 10 %. This shows that even a low shear stress can result in content release from the internal droplet phase. The experimental emulsion release study is supported by a numerical simulation of drop deformation and break‐up under shear stress.

Controlling the Stability and Rheology of Copolyol Dispersions in Fatty Alcohol Ethoxylate (AEO9)-Stabilized Multiple Emulsions

“…Concerning the multiple emulsions sheared at 3000 rpm, there was no noticeable destruction of compartmented layers; instead, the applied shear contributed to the reduction of oil globules that improved the storage stability of multiple emulsions (Figure e,j). The decrease in droplet size and uniformity obtained might be due to the interaction of water molecules and the outer emulsifier AEO9 (via polyethylene oxide group) thickening property when shear is introduced to the emulsion system . As can be seen, when the external shear increased to 5000 rpm, the reduction in oil droplets size was viewed as shown by the optical microscope (Figure k).…”

Continuous Multistep Encapsulation Process for the Generation of Multiple Emulsions

“…However, this is still in the margin of the error and, thus, cannot conclusively be related to the droplet breakup due to crossflow. Results in literature substantiate this assumption 20, 30.…”

“…It has been concluded that the membrane porosity has a significant influence on the droplet size distribution. Luhede and Fritsching [20] employed sintered glass membranes with a crossflow to produce W 1 /O/W 2 emulsions. The shear stability was investigated, showing that surfactant concentration and shear rate influence the EE significantly.…”

Static-state particle fabrication via rapid vitrification of a thixotropic medium

“…Throughout an emulsion process, sedimentation or creaming of the distributed phase (emulsion droplets) after their creation and prior to their solidification result in droplet coalescence, causing irregular clumps of particles and potentially ruining the overall particle batch 23 , 24 . This phenomenon is usually prevented by stirring the continuous phase until the distributed droplets are fully solidified 25 – 27 , but this redundant shearing causes the droplets to collide and deform, ultimately leading to low process yield and high particle heterogeneity. One proposed solution to this challenge is to fix and isolate each droplet in place by vitrifying the continuous phase after emulsification.…”