Contact angle associated with thin liquid films in emulsions
The surface tension of liquid film can be very different from the surface tension of the liquid in bulk, because of contributions from the disjoining pressure. The authors described a method to measure the surface tension of a liquid film easily by measuring the contact angle formed between the film and the plateau border. The authors showed how the contact angle is related to the disjoining pressure and demonstrated how temperature and different salt concentrations changes the surface tension of liquid film.
The tension of the film, γf is related to the bulk interfacial tension γ by
where h is the film thickness, he is the equilibrium thickness and π is the disjoining pressure. Whenever ΔF < 0, the two bulk surfaces will, on macroscopic scale, intersect an angle 2θ (see figure 1), such that
ΔF essentially determines whether the oil droplets will repel or spontaneously flocculate as in figure 2. For ΔF < 0, we can precisely determine the value of ΔF just by measuring the macroscopic contact angle by equation (3).
1. Contact angles associated with thin liquid films in emulsions, Aronson and Princen, Nature 1980