Paint drop spreading on wood and its enhancement by an in-plane electric field

Experimental observations of drops of water with aniline dye softly located or impacting onto balsa wood substrates were used to elucidate the effect of an in-plane electric field (at a high voltage of 10 kV applied) on drop behavior. The top and side views were recorded simultaneously. The short-term recordings (on the scale of a few ms) demonstrated a slight effect of the applied in-plane electric field. In some trials, a greater number of finger-like structures were observed along the drop rim compared to the trials without voltage applied. These fingers developed during the advancing motion of the drop rim. The long-term recording (on the scale of ∼10 s) was used to evaluate the wettability-driven increase in the area-equivalent radius of the wetted area. These substrates had grooves in the inter-electrode or the cross-field directions. The groove directions affected the wettability-driven spreading and imbibition. The wettability-driven spreading in the long term was a much more significant effect than the effect of the electric field, because the imbibition significantly diminished the drop part above the porous surface, which diminished, in turn, the electric Maxwell stresses, which could stretch the drop. A simplified analytical model was developed to measure the moisture transport coefficient responsible for liquid imbibition in these experiments. Furthermore, the phase-field modeling of drops on balsa was used to illustrate how a change in the contact angle from hydrophobic to hydrophilic triggers drop imbibition into balsa wood.