Design Parameters for

Tuteja, A., Choi, W., McKinley, G.H., Cohen, R.E. and Rubner, M.F.

Recent experiments have revealed that the wax on the lotus leaf surface, by itself,
is weakly hydrophilic, even though the lotus leaf is known to be superhydrophobic.
Conventional understanding suggests that a surface of such waxy composition should
not be able to support superhydrophobicity and high contact angles between a liquid
and the surface. Here, we show that the unexpected superhydrophobicity is related to
the presence of “reentrant texture” (that is, a multivalued surface topography) on the
surface of the lotus leaf. We exploit this understanding to enable the development of
superoleophobic surfaces (i.e., surfaces that repel extremely low-surface-tension liquids,
such as various alkanes), where essentially no naturally oleophobic materials exist. We
also develop general design parameters that enable the evaluation of the robustness of
the composite interface on a particular surface. Based on these design parameters, we
also rank various superhydrophobic and superoleophobic substrates discussed in the
literature, with particular emphasis on surfaces developed from inherently hydrophilic
or oleophilic materials.