Three stages of Marangoni-driven film spreading for miscible fluids

The Marangoni-driven film spreading in the fully miscible droplet–reservoir system was experimentally studied. Three stages of film spreading were identified over a relatively long time, with the power-law exponent n (R ∼ tn, R is film radius, t is time) nonmonotonically transitioning from 3/4, to 1/4, and back to 3/4. The variation of the Marangoni stress was found to be responsible for the three-stage power-law relationships, with the tangential stretching effect of the expanding liquid–air interface governing stages I and III and the normal diffusion effect dominating stage II. This work presents a unified interpretation of the inconsistent power-law relationships reported from previous studies on Marangoni-driven film spreading for miscible fluids.