M. Vis1*[§], R.H. Tromp1,2, B.H. Erné1
1 Van ’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
2 NIZO food research, Kernhemseweg 2, 6718 ZB Ede, The Netherlands
Solutions of two different polymers in water commonly phase separate above a certain total polymer concentration, typically 10% by mass, and the two resulting coexisting phases are each enriched in one of the polymers. The water–water interface has many peculiar properties, such as an electric potential step, an ultralow interfacial tension, and a width of the order of ten nanometer, complicating the preparation of stable water-in-water emulsions.
We found that ultrathin colloidal platelets are effective stabilizers of water-in-water emulsions. Because the rim of plate-like particles accommodates (nearly) any contact angle, they surprisingly feature stronger adsorption than spheres of equal surface area. Moreover, the nanoplatelets have a low buoyant mass that preserves slow sedimentation of the nearly density matched emulsion. Our conclusions are underpinned with detailed experiments on the physical chemistry of our novel water-in-water emulsions.
[§] present address: Physical Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands