Millimeter-Sized Hole Damming

Valves
used to control liquid filling and draining processes from
storage typically need to be actuated. Here, we show that similar
flow enabling and restricting operations can be achieved through millimeter
scale holes that function according to the amount of hydrostatic pressure
applied without any other intervention. This phenomena is exhibited
using receptacles where the base is made of either a hydrophilic or
superhydrophobic substrate with hole sizes ranging from 1.0–2.0
mm. The construction is such that the drainage flow velocities are
of the same order in both substrates and follow Torricelli’s
law trends. Nevertheless, the primary mechanisms responsible for resisting
the onset of flow in each substrate are different; nonbreaching of
the advancing contact angle threshold in the former, and stable maintenance
of an elastic-like deformation of the liquid–gas interface
that is connected to the surrounding plastron in the latter. These
differences are demonstrated using an upward jet of water delivered
to the orifice, where a discharging flow from the hydrophilic base
occurred before the threshold hydrostatic pressure condition was attained,
while liquid from the jet is subsumed into the liquid body of the
receptacle with the superhydrophobic base without any leakage. These
findings portend advantages in simplicity and robustness for a myriad
of liquid-related processes.