Dynamics of flocculation due to an added immiscible liquid

The dynamics and instability of liquid films coating two solid particles that approach each other with a certain normal velocity are investigated. Depending on the values of various physicochemical parameters and velocity of approach and initial separation, there are two possible outcomes of this encounter, namely, either the rupture of the film (dewetting) or the coalescence of the two unruptured film surfaces takes place. Based on the magnitudes of the parameters, conditions are derived for the prediction of whether dewetting or coalescence occurs. While the present results are most germane to coagulation of particles in a gas (or condensable vapor), they also provide a qualitative understanding of flocculation in a liquid medium (by the addition of a preferentially wetting immiscible liquid phase). Some insight is also gained regarding the separation of multicomponent solids by preferential flocculation. Based on the dynamics and time of coalescence of the two approaching fluid films, a method is also suggested for the experimental determination of the Hamaker constant