Sticky Superhydrophobic\nState

It is common sense that the droplet is stickier to substrates\nwith\nlarger solid–liquid contact areas. Here, we report that this\nintuitive trend reverses for hollowed micropillars, where a decrease\nin solid–liquid contact area caused by an increase in the pore\nsize of a pillar top leads to an increase in the droplet depinning\nforce. As compared to relief of liquid–vapor interface distortion\ncaused by the sliding of the contact line on filled pillars, the pore\nhinders the contact line sliding, hence leading to enhanced interface\ndistortion and droplet adhesion. The droplet on hollowed micropillars\nis completely suspended above the vapor but inherently sticky. Hence,\nthis counterintuitive phenomenon is termed as the sticky superhydrophobic\nstate in contrast to the conventional superhydrophobic state with\nlow adhesion. A model building upon the dynamics of the contact line\nand liquid–vapor interface, which successfully predicts the\ndroplet depinning force on filled and hollowed pillars, is introduced.