Designing Laplace Pressure Pattern for Microdroplet Manipulation

Manipulation of arrayed tiny droplets is important in liquid dispersion, liquid transportation, bioassays, nucleation, integrated electronics, and various lab experiments that require delivering precise and minute volumes of droplets. Liquid dispensed from a small orifice or split from surface patterns are typical methods, but the acquired droplet diameters are similar to that of the nozzle and pattern. Here we demonstrate that tiny droplets with dimensions much smaller than the pattern can be arrayed advantageously through designing a Laplace pressure pattern based on conical morphology and wetting heterogeneity. The pattern could selectively resist liquid's motion and drive the capillary bridge breaking of macrodrop into arrayed tiny droplets at wettability boundaries. Arrayed picoliter droplets can be acquired on a submillimeter-scaled pattern with a feature size of several hundred micrometers. Through regulating the conical morphologies and the wetting heterogeneity, the volume and number of tiny droplets can be accurately controlled. As a paradigm, adopting droplets of nanoparticle dispersion, various arrayed functional assemblies can be fabricated. This integration of conical morphology and wetting heterogeneity offers a powerful kit for patterned microdroplets quantitative and locational manipulation and opens a new avenue to achieve functional units in a facile and high-throughput way.