Jump-to-Contact between Viscous Drops under van der Waals Attraction*

The coalescence of viscous drops is significantly affected by any drop deformation prior to contact. For slowly moving drops in close proximity, van der Waals attraction between the drops overcomes surface tension and initiates a dynamic 'jump-to-contact' process where the van der Waals attraction deforms the drops' surfaces so that they make contact. This process sets the initial surface profile for the subsequent coalescence of the drops.

This talk will discuss the jump-to-contact process across an inviscid gap, showing that as contact is approached the dynamics are self-similar with both the radial and gap scales varying as t'^1/3. for time until contact t'. The leading order balance is between van der Waals attraction and viscous forces. Although surface tension is subdominant, it selects the observed t'^1/3 behaviour from a continuous range of possible time-exponents. Interestingly, the self-similar profiles are non-universal and retain some memory of the initial conditions. The self-similar surface profiles will inform suitable initial conditions for subsequent drop coalescence.