Demixed phases of colloid plus polymer systems in a common solvent Calculation of the interfacial tension

An analytical formula for the interfacial tension of the (sharp) interface in a demixed (complex) system of colloid and polymer has been derived. The colloid and polymer are modelled as hard spheres and overlapping spheres, respectively. The treatment is based on a recent theory of Kalikmanov and Hofmans, in which the pair potential is modelled as a depletion potential. For example, a hard sphere with a diameter of 10 nm gives an interfacial tension between, say, 0.015 and 0.055 mN/m (=dyne/cm) depending on the concentration and the size of the polymer.