The role of monolayer viscosity in Langmuir film hole closure dynamics

TL;DR

This paper revisits a model of hole closure in Langmuir films, incorporating monolayer viscosity, revealing significant corrections to dynamics and suggesting higher edge tension values than previously estimated.

Contribution

It introduces monolayer viscosity into the model of Langmuir film hole closure, providing more accurate predictions and explaining experimental deviations.

Findings

Viscosity-dependent corrections are significant even at small viscosities.

Estimated edge tension can be up to eight times larger (~5.5 pN) than earlier reports.

Corrections explain deviations from inviscid model predictions.

Abstract

We re-examine the model proposed by Alexander et al. (2006) for the closing of a circular hole in a molecularly thin incompressible Langmuir film situated on a Stokesian subfluid. For simplicity their model assumes that the surface phase is inviscid which leads to the result that the cavity area decreases at a constant rate determined by the ratio of edge tension to subfluid viscosity. We reformulate the problem, allowing for a regularizing monolayer viscosity. The viscosity-dependent corrections to the hole dynamics are analyzed and found to be nontrivial, even when the monolayer viscosity is small; these corrections may explain the departure of experimental data from the theoretical prediction when the hole radius becomes comparable to the Saffman-Delbruck length. Through fitting, we find the edge tension could be as much as eight times larger (~5.5 pN) than previously reported under these relaxed assumptions.