Ultrastable Water‐in‐Water Emulsions by Addition of Polyion Complex Micelles
Abstract
We report the use of polyion complex micelles (PICM) obtained by complexation of poly(sodium acrylate) and poly(N‐methyl‐2‐vinylpyridinium iodide‐block‐ethylene oxide) as novel stabilizers for water‐in‐water emulsions consisting in poly(ethylene oxide) (PEO) and dextran mixtures in water. PICM concentrations as low as 1 g/L lead to a strong increase of stability for both PEO‐in‐dextran and dextran‐in‐PEO emulsions, as they did not display any macroscopic phase separation after several months. Such long term stability is to our knowledge unprecedented in the literature dedicated to water‐in‐water emulsions. Moreover, increasing the concentration of PICM further induces a decrease in the droplet size, resulting in a strong reduction of the cream‐ing or sedimentation rates, and suppression of the coalescence after a few days. The dissociation of PICM at high salt concentration was taken as an opportunity to trigger the destabilization of the water‐in‐water emulsions by addition of a concentrated salt solution. PEO‐in‐dextran emulsions displayed more sensitivity to PICM and salt concentrations than dextran‐in‐PEO emulsions, in terms of both stability and droplet size, indicating that the underlying stabilization mechanisms are different for the two systems.