Surface for directional fluid transport

A substrate for directional transport of a fluid having a contact angle θ, the substrate comprising a capillary structure for passive, directional fluid transport, the capillary structure comprising a capillary having a forward direction and a backward direction, the capillary comprising first and second capillary units each having a sequence of capillary components including a connective section in fluid communication with a diverging section, the diverging section having a forward side and dimensions inducing a concave meniscus in the forward direction, wherein the connective section of the second capillary unit is connected to the forward side of the diverging section of the first capillary unit to form at least one transition section, and wherein a change in the dimensions in the transition section induces in the backward direction a convex liquid meniscus or a straight liquid meniscus with an infinite radius of curvature.

A capillary structure for passive directional transport of a fluid having a contact angle θ with regard to the capillary structure, the structure comprising:

• a capillary comprising a plurality of capillary units each having a sequence of capillary components including a connective section in fluid communication with a diverging section, the diverging section followed by a transition section,
• wherein the connective section has an aspect ratio aconnective>½((1/cos θ)−1), wherein the diverging section diverges from the connective section at an angle α such that α/2<π/2−θ, and wherein the transition section incorporates an abrupt change in width from the diverging section of one capillary unit to the connective section of the next capillary unit.