Inertial and viscous dynamics of jump-to-contact between fluid drops under van der Waals attraction

When two small fluid drops are sufficiently close, the van der Waals force overcomes surface tension and deforms surfaces into contact, initiating coalescence. The dynamics of deformation across an inviscid gap falls distinct regimes (Stokes inertial–viscous) characterized by forces that balance attraction at leading order (viscosity, both inertia viscosity). previously studied Stokes regime holds for very viscous but fails less as becomes significant before contact is reached. We show subsequent inertial–viscous self-similar approached, with width decreasing $t{'^{3/8}}$ radial scale deformed region $t{'^{1/2}}$ $t{'}\to 0$ , time until $t'$ . behaviour universal generic asymptotic observed in time-dependent simulations. unique profile suggests new initial conditions coalescence after contact.