The transport of a small amount of liquid on a solid is not a simple proces
s, owing to the nature of the contact between the two phases. Setting a liq
uid droplet in motion requires non-negligible forces (because the contact-a
ngle hysteresis generates a force opposing the motion(1)), and often result
s in the deposition of liquid behind the drop. Different methods of levitat
ion-electrostatic, electromagnetic, acoustic(2), or even simpler aerodynami
c(2,3) techniques-have been proposed to avoid this wetting problem, but all
have proved to be rather cumbersome. Here we propose a simple alternative,
which consists of encapsulating an aqueous liquid droplet with a hydrophob
ic powder. The resulting 'liquid marbles' are found to behave like a soft s
olid, and show dramatically reduced adhesion to a solid surface. As a resul
t, motion can be generated using gravitational, electrical and magnetic fie
lds. Moreover, because the viscous friction associated with motion is very
small(4), we can achieve quick displacements of the droplets without any le
aks. All of these features are of potential benefit in microfluidic applica
tions, and also permit the study of a drop in a non-wetting situation-an is
sue of renewed interest following the recent achievement of super-hydrophob
ic substrates(5).