Current opinion in superspreading mechanisms.

BACKGROUND

An aqueous solution of trisiloxane-ethoxylate surfactants (superspreaders) has fascinating surface properties that promote rapid spreading over a large area of difficult-to-wet substrates. The overall spread area achieved by an aqueous droplet containing superspreaders can be as much as 50 times greater than water, and 25 times more effective than a conventional surfactant on a leaf's surface. The phenomenon that drives superspreading is still not well understood and it is under continuous discussion.

CONCEPTS AND MODELS

The goal of this paper is to review the data published to elucidate the concepts and mechanisms presented in the literature and to propose a model for superspreading.

CONCLUSIONS

A simple model was proposed concerning the surface tension gradient (or Marangoni flow) over the curved droplet surface when the value of the wetting angle was considered. The model predicted the optimum rate of spreading vs. angle at θ = 60° and was in a satisfactory agreement with the experimental observations.