  We report experimental observation of a kind of fast spontaneous movements of
water drops on surfaces of cones with diameters from 0.1 to 1.5 mm. The
observed maximum speed (0.22 m/s) under ambient conditions were at least two
orders of magnitude higher than that resulting from any known single
spontaneous movement mechanism, for example, Marangoni effect due to gradient
of surface tension. We trapped even higher spontaneous movement speeds (up to
125 m/s) in virtual experiments for drops on nanoscale cones by using molecular
dynamics simulations. The underlying mechanism is found to be universally
effective - drops on any surface either hydrophilic or hydrophobic with varying
mean curvature are subject to driving forces toward the gradient direction of
the mean curvature. The larger the mean curvature of the surface and the lower
the contact angle of the liquid are, the stronger the driving force will be.
This discovery can lead to more effective techniques for transporting droplets.
