Can Superhydrophobic Surfaces Repel Hot Water?
I’ll admit that while I have studied the hydrophobicity of surfaces in the past, I’ve never thought of the question of whether or not superhydrophobic surfaces can repel hot water. My initial answer was, “Isn’t it obvious? I mean, why wouldn’t it?”
When drops of water fall onto a surface, it will (generally) either spread over the surface or will simply roll/bounce off the surface. The latter case describes a concept called hydrophobicity, a material’s tendency to repel water. Different materials can have different degrees of hydrophobicity.
Leaves (e.g. lotus leaves, as illustrated above) are a nice example of hydrophobic material. Interestingly, as a result of a change in temperature of the water, the droplets of water (25 °C) are more spherical in the left photo, while the droplets of water (55 °C) are more spread out in the right photo (Liu et al.). The respective SEM (scanning electron microscopy) photos are directly below. Liu et al. suggest that the hot water destroy/alter the surface of the material, thus changing its hydrophilic properties.
While yes, superhydrophobic surfaces can repel hot water, it appears as thought the degree of hydrophobicity changes with an increase in temperature. However, the story changes with man-made hydrophobic materials ;)
Liu, Y.; Chen, X.; Xin, J.H. PCan superhydrophobic surfaces repel hot water? J. Mater. Chem. 2009, 19, 5602-5611. DOI: 10.1039/B822168E