Rapid Fabrication of T-Shaped Micropillars on Polypropylene Surfaces with Robust Cassie-Baxter State for Quantitative Droplet Collection

Applying microinjection compression molding technology, a fast and flexible method is first proposed for the successive and mass replication of polypropylene surfaces with T-shaped micropillars in the present work. The water droplet on the titled surfaces grows in size to roll off due to gravitation effect. Interestingly, the roll-off angles on such surfaces are as a quadratic function of specified water droplet volume, meaning quantitative droplet collection and lossless transfer can be performed on the replicated surfaces. Meanwhile, self-cleaning behavior is preserved on the surfaces. Moreover, the robust Cassie Baxter state on the replicated surfaces against the external pressure is demonstrated with droplet compression and immersion experiments. Specifically, a droplet sitting on the replicated surface can recover its spherical shape after squeezed to a water-film as thin as 0.37 mm, and the replica is remained fully spotless after it is submerged into dyed water. The proposed method for fast replication of microstructured surfaces can be an excellent candidate for the development of microfluidics and droplet manipulation.