Electrostatic precursor films†
When a liquid spontaneously spreads over a solid surface, a progressive microscopic structure, conventionally known as a van der Waals driven precursor film, develops ahead of the moving contact line. Here, we report a new class of electrostatically assisted precursors containing microscopic charged particles. This precursor manifests itself at the late stage of forced-spreading of a macroscopic dielectric film subjected to a unipolar ionic discharge in a gas containing particulate. We put a model forward to predict dynamic behaviour of this electrostatic precursor. The spreading of the precursor film is predicted to be proportional to the square root of the exposure time, which is consistent with the ellipsometric measurements.