  The relation between the contact angle of a liquid drop and the morphological
parameters of self-affine solid surfaces have been investigated. We show
experimentally that the wetting property of a solid surface crucially depends
on the surface morphological parameters such as: (1) root mean square (rms)
roughness $\sigma$, (2) in-plane roughness correlation length $\xi$ and (3)
roughness exponent $\alpha$ of the self-affine surface. We have shown that the
contact angle monotonically decreases with the increase in the rms local
surface slope $\rho$ ($\propto \sigma/\xi^\alpha$) for the cases where the
liquid wets the crevices of the surface upon contact. We have shown that the
same solid surface can be made hydrophobic or hydrophilic by merely tuning
these self-affine surface morphological parameters.
