Influence of Substrate Conductivity on Circulation Reversal in Evaporating Drops

Nonuniform evaporation from sessile droplets induces radial convection within the drop, which produces the well-known ‘‘coffee-ring’’ effect. The evaporation also induces a gradient in temperature and consequently a gradient in surface tension, generating a Marangoni flow. Here we investigate theoretically and experimentally the thermal Marangoni flow and establish criteria to gauge its influence. An asymptotic analysis indicates that the direction of the flow depends on the relative thermal � ;