  This progress report summarizes recent studies of electrochemical oxidation
to modulate the interfacial tension of gallium-based alloys. These alloys,
which are liquid at ambient conditions, have the largest interfacial tension of
any liquid at room temperature. The ability to modulate the tension offers the
possibility to create forces that change the shape and position of the metal.
It has been known since the late 1800s that electrocapillarity-the use of
potential to modulate the electric double layer on the surface of metals in
electrolyte-lowers the interfacial tension of liquid metal. Yet, this
phenomenon can only achieve modest changes in interfacial tension since it is
limited to potential windows that avoid reactions. A recent discovery suggests
that reactions driven by the electrochemical oxidation of gallium alloys cause
the interfacial tension to decrease from ~500 mN/m at 0 V to ~0 mN/m at ~0.8 V,
a change in tension that goes well beyond what is possible via conventional
electrocapillarity or surfactants. The changes in tension are reversible;
reductive potentials return the metal back to a state of high interfacial
tension. This report aims to summarize key work and introduce beginners to this
field by including electrochemistry basics while addressing misconceptions. We
discuss applications that utilize modulations in interfacial tension of liquid
metal and conclude with remaining opportunities and challenges that need
further investigation.
