Wettability influence on the onset temperature of pool boiling: experimental evidence onto ultra-smooth surfaces

In this article we study systematically the effect of wettability on the onset of boiling on the same nanometrically smooth surface. By grafting different monolayers of molecules, we were able to explore the wettability from the equilibrium static contact angle, θ0 = 0° to θ0 = 110°, without changing the surface topography. The superheat temperature at the onset of pool boiling was measured and eventually a non-classical trend of T(ONB) as a function of wettability was observed. The nucleation site densities for the different grafting cases were also measured by image analysis. Moreover, we propose a novel theoretical interpretation to this phenomenon linking nucleation and the molecular diffusion coefficient. MD simulation results support this approach.