Controlling Nanodrop Passage through Capillary Nanovalves by Adjusting Lyophilic Crevice Structure

The passage or blockage of nanodrops through a nanovalve made of a nanocrevice is explored by proof-of-concept simulations, including many-body dissipative particle dynamics and Surface Evolver simulations. Although it is generally believed that the drops wet lyophilic crevices readily, we show that the penetration of the drops into such crevices with specific structures can be prevented. The morphological phase diagram in terms of the contact angle (θ_Y) and wedge angle (α) are constructed, and three regimes are identified: non-penetration and partial penetration, in addition to complete penetration. It is interesting to find that as long as α is small enough, the drop always runs away from the crevice even on lyophilic surfaces, leading to the non-penetration state. For intermediate α and small θ_Y, the drop tends to break up, and only a portion of liquid wets the crevice, corresponding to the partial penetration state. Our simulation results demonstrate that a lyophilic capillary nanovalve for controlling the droplet passage can be fabricated by simply adjusting the wedge angle of the crevice.