posted on 2013-09-10, 00:00authored byZhe Shen, Huai Sun, Xiaoyan Liu, Wenting Liu, Ming Tang
The stability of Newton black films
(NBFs) under lateral mechanical
stretch was investigated by nonequilibrium molecular dynamics (NEMD)
simulations using force field parameters validated by accurate prediction
of surface tensions. The applied strains accelerated film ruptures,
enabling efficient measurements of the critical thicknesses of the
films. Two representative surfactants, sodium dodecyl sulfate (SDS)
for ionic surfactant and pentaethylene glycol monododecyl ether (C12EO5H) for nonionic surfactant, were investigated
and compared. The predicted critical thickness of C12EO5H-coated film is smaller than that of the SDS-coated film,
which is consistent with previously reported experimental observations.
Our simulation results show that while the two surfactant-coated films
exhibit similar dynamic properties attributed to the Marangoni–Gibbs
effect, their surface structural characteristics are quite different.
Consequently the two films demonstrate distinct rupture mechanisms
in which rupture starts at uncovered water domains in the SDS-coated
film, but at lateral surfactant/water interfaces in the C12EO5H-coated film. Our findings provide new insights into
the stabilization mechanisms of NBFs and will facilitate the design
and development of new films with improved properties.