A curled open capillary tube for selective directional liquid transport

Directional liquid transport plays a critical role in many fields, especially in microfluidics and biochemical reagent analysis. How to achieve selective directional transport of different liquids through a simple microstructural surface is still a challenge. In the present paper, a novel open capillary tube with an egg-roll-like shape is designed and fabricated, which is composed of two semi-circular capillary tubes with different radii and an array of inclined microplates distributed on their inner surface. Different from the traditional capillary tube with constant radius, water transports along the inclined direction of the microplate, while the ethanol does in reverse in this curled open capillary tube. It is found that the selective transport direction is determined by the liquid-capillary contact configuration, which depends on both the inclination angle of the microplate and the contact angle of different liquids. The critical liquid contact angle that governs the selective direction and the transport displacement of liquids is predicted theoretically, which is well consistent with the experimental measurements. Based on the above mechanism, several potential application scenarios of the as-fabricated curled open capillary tube are further proposed, including the microfluidic channel diversion and reagent fusion reaction. The obtained results can provide an innovative prototype for the flexible manipulation of various liquids.