Effect of an encapsulated bubble in inhibiting droplet sliding.

The transport of liquid droplets on surfaces carrying reactants offers advantages in the creation of fluidic devices crucial for life science applications. In a majority of situations, a selection of these droplets on a surface, rather than all of them, will need to be moved at any one time. It is a formidable challenge to deliver the motive energy source only to specific droplets while leaving the others unmoved. Here, we describe an alternative novel solution of momentarily pinning specific droplets to the surface while allowing the rest to be moved. We demonstrate this concept via the injection of a sizable bubble that is attached to a PTFE surface within a droplet. This then affects the contact line of the droplet, pinning it despite the introduction of an incline that will normally result in sliding. The use of bubbles offers easy release of pinning at will by simple rupture using mechanical means.