Effect of droplet size on the rheological properties of highly-concentrated w/o

Rheological properties of highly concentrated emulsions of the water-in-oil type were studied. Wa- ter phase (concentration approxi- mately 91%) consists of a supersaturated aqueous solution of nitrate salts; water comprises less than 20% by mass. The average size of droplets, D, in the emulsions was varied. It was found that the emul- sions are non-Newtonian liquids and flow curves measured in a sweep re- gime of shearing have clear low- shear-rate Newtonian domain. The complete flow curves are fitted by the Cross equation. The elastic modulus is practically constant in a very wide frequency range. Hence the viscoelastic relaxation processes might be expected at times >>100 s and in the short-term side of the curve at approximately 0.01 s. The elastic modulus (measured in oscil- lating testing and in elastic recovery as well) is proportional to D -2 while the Newtonian viscosity is propor- tional to D )1 . The time effects were observed: it was found that the emulsions behave as rheopectic materials because prolonged shearing results in an increase of viscosity in the low shear rate domain of several orders of magnitude.