The electrohydrodynamic stability of a liquid bridge was studied in steady and
oscillatory axial electric fields with a novel apparatus aboard a space shuttle. To
avoid interphase transport, which complicates matters in terrestrial, matched-density
systems, the experiments focused on a liquid column surrounded by a dielectric gas.
The micro-gravity acceleration level aboard the spacecraft kept the Bond number
small; so interface deformation by buoyancy was negligible. To provide microgravity
results for comparison with terrestrial data, the behaviour of a castor oil bridge in a
silicone oil matrix liquid was studied first. The results from these experiments are in
excellent agreement with earlier work with isopycnic systems as regards transitions
from a perfect cylinder to the amphora shape and the separation of an amphora into
drops. In addition, the location of the amphora bulge was found to be correlated with
the field direction, contrary to the leaky dielectric model but consistent with earlier
results from terrestrial experiments. Next, the behaviour of a bridge surrounded by a
dielectric gas, sulphur hexa fluoride (SF6), was investigated. In liquid–gas experiments,
electrohydrodynamic ejection of liquids from ‘Taylor cones’ was used to deploy
fluid and form bridges by remote control. Experiments with castor oil bridges in
SF6 identified the conditions for two transitions: cylinder–amphora, and pinch-off.
In addition, new behaviour was uncovered with liquid–gas interfaces. Contrary to
expectations based on perfect dielectric behaviour, castor oil bridges in SF6 could not
be stabilized in AC fields. On the other hand, a low-conductivity silicone oil bridge,
which could not be stabilized by a DC field, was stable in an AC field.