Gravitational Drainage of Thin Films of Trisiloxane-(Poly)ethoxylate Superspreaders

TL;DR

This study compares the drainage behavior of superspreader and non-superspreader thin films, revealing that superspreaders stabilize at thinner thicknesses due to disjoining pressure, which extends film lifetime and affects pattern formation.

Contribution

It demonstrates the role of disjoining pressure in stabilizing superspreader films and introduces gravitational drainage as a method to measure this pressure.

Findings

Superspreader films show turbulent interferometric patterns unlike non-superspreaders.

Superspreader films stabilize below 50 nm thickness and last longer before bursting.

Disjoining pressure from van der Waals forces explains superspreader film stabilization.

Abstract

Gravitational drainage of vertical films supported on a wire frame of superspreader SILWET L-77 and its cousin non-superspreader SILWET L-7607 revealed drastic differences. The superspreader films showed complicated dynamic turbulent-like interferometric patterns in distinction from the ordered color bands of the cousin non-superspreader which reminded those of the ordinary surfactants. Nevertheless the superspreader films stabilized themselves at the thickness below 50 nm and revealed an order of magnitude longer life time before bursting compared to the cousin non-superspreader. Notably, the superspreader revealed drastic differences from the non-superspreader in aqueous solutions with no contact with any solid Teflon surface. The theoretical part of the work attributed the self-stabilization of the superspreader films to significant disjoining pressure associated with the van der Waals repulsion of the fluffy surfaces of the film formed by long superspreader bilayers hanging from the free surfaces. The non-superspreaders do not possess any significant disjoining pressure in the film with thicknesses even in the range 30-50 nm. The results show that gravitational drainage of vertical films is a useful simple tool for measuring disjoining pressure.