Master curves for elastic and plastic properties of highly concentrated emulsions

20 Oct 2015

Critical comparison of dependences of elastic and plastic properties of highly concentrated emulsions (so-called ?compressed? emulsions) on the concentration and droplet sizes is performed. The studied emulsions of water-in-oil type are so-called ?liquid explosives.? They are characterized by different mean sizes and different droplet size distributions of the dispersed phase. Different average values (Dav, D32, and D43) are used as characteristics of droplet sizes. Experiments are carried out with emulsions of two concentrations. Aqueous phase (dispersed droplets) is presented by supercooled solutions of inorganic salt in water in a metastable state. The concentration limit of the existence of highly concentrated emulsions is determined by the condition of the closest packing of liquid droplets, which lies in the ?* = 0.77?0.80 range. In addition, there is a limiting value of the maximal size of droplets. This limiting value depends on the concentration and meets the requirement that droplets should be small enough for the solution to exist in a supercooled state. The elastic modulus and the yield stress of emulsions studied are proportional to the square of the reciprocal linear size of droplets, which contradicts some theoretical models, according to which these parameter should be proportional to the reciprocal size of droplets. Using the obtained experimental data, we constructed generalized dependences of the elastic modulus and the yield stress on the concentration and size of droplets. These characteristics are in good agreement with the experimental data