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In this fluid dynamics video, we report on experiments of large aspect ratiocapillary surfaces supported by a helical wire. These open channels arepotentially useful for fluid management at low Bond numbers. The experimentswere performed in a Plateau tank, injecting 2-fluorotoluene into distilledwater, density matched at 26.5 $^{o}$C. Extension springs with a nominaldiameter of 0.24 inches and with a wire diameter of 0.018 inches were used. Atsmall extensions, liquid can be injected into the spring from one side. Theinjected free-ended liquid columns are stable. Volume-constrained stability canbe studied after injecting from both sides until coalescence. Stable statesexist between lower and upper volume stability limits. The low volumeinstability is manifested by the growth of a neck that eventually breaks. Thebreakage sends a wave front; the interface ahead of the front is static whilethe interface behind the front undergoes oscillations. These oscillationseventually dampen as the free-ends retract until equilibrium states arereached. The upper volume instability causes the interface to blow out creatinga large drop that remains connected to the liquid column supported by thespring. After a critical pitch, injection is no longer possible from one end.However, a liquid column established by injection can be stretched beyond thecritical pitch for injection. Beyond this pitch, after breakup and blowout theinterface undergoes a pearling instability. The resulting free ends retract andgrow into drops from which the liquid column eventually breaks. This pearlinginstability propagates throughout the entire length of the structure largelyemptying it. Small tracer drops, outside and in the vicinity of the interface,traced helical trajectories as liquid was injected into, and withdrawn from,the spring. We also demonstrated vertical wicking into a small spring in air.

Stability of capillary surfaces supported by a helical wire