Controlling adhesion using AC electric fields across fluid films

Abstract

We demonstrate reversible and switchable actuation using AC electric fields to bring two surfaces separated by a thin film of ionic fluid in and out of adhesive contact. Using a Surface Force Balance we apply electric fields normal to a crossedcylinder contact and measure directly the adhesive force and surface separation with sub-molecular resolution. Taking advantage of the oscillatory structural force acting between the surfaces across the fluid, which we show to be unaffected by the AC field, we pick between the distinct (quantized) adhesive states through precise tuning of the field. This proof-of-concept indicates exquisite control of surface interactions using an external field.

Electrotunable friction with ionic liquid lubricants

“…Moreover, electrotunable lubrication relies on controlling surface charges, which can be readily adjusted only on metal or metallized surfaces and coatings. The use of AC fields can open up a new way to tune surface interactions and friction 30,53,54 .…”

“…Until now, only a couple of experiments used a setup of this sort: one experiment involving a confined polyelectrolytic film 49 demonstrated an 80% reduction in friction using an alternating electric field. This exciting result, combined with emerging evidence that AC electric fields cause very large repulsive forces across ionic films, signals strong prospects for AC-controlled friction 30,53,54 ; to date it remains to be demonstrated if EF with pure RTILs can be realized in this way.…”

“…AC signal with frequencies faster than the timescale of electrical double layer charging, to avoid electrical breakdown and to reach more complex effects , are clearly possible and are envisaged as a powerful tool for tuning surface interactions and friction 30,53,54 .…”