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Transient responses of a wetting film to mechanical and electrical perturbations

journal contribution
posted on 06.12.2017, 00:00 by R Manica, Jason ConnorJason Connor, L Clasohm, S Carnie, R Horn, D Chan
This article reports real-time observations and detailed modeling of the transient response of thin aqueous films bounded by a deformable surface to external mechanical and electrical perturbations. Such films, tens to hundreds of nanometers thick, are confined between a molecularly smooth mica plate and a deformable mercury/electrolyte interface on a protuberant drop at a sealed capillary tube. When the mercury is negatively charged, the water forms a wetting film on mica, stabilized by electrical double layer forces. Mechanical perturbations are produced by driving the mica plate toward or by retracting the mica plate from the mercury surface. Electrical perturbations are applied to change the electrical double layer interaction between the mica and the mercury by imposing a step change of the bias voltage between the mercury and the bulk electrolyte. A theoretical model has been developed that can account for these observations quantitatively. Comparison between experiments and theory indicates that a no-slip hydrodynamic boundary condition holds at the molecularly smooth mica/electrolyte surface and at the deformable mercury/electrolyte interface. An analysis of the transient response based on the model elucidates the complex interplay between disjoining pressure, hydrodynamic forces, and surface deformations. This study also provides insight into the mechanism and process of droplet coalescence and reveals a novel, counterintuitive mechanism that can lead to film instability and collapse when an attempt is made to thicken the film by pulling the bounding mercury and mica phases apart.

Funding

Category 1 - Australian Competitive Grants (this includes ARC, NHMRC)

History

Volume

24

Issue

4

Start Page

1381

End Page

1390

Number of Pages

10

ISSN

0743-7463

Location

United States

Publisher

American Chemical Society

Language

en-aus

Peer Reviewed

Yes

Open Access

No

External Author Affiliations

National University of Singapore; Process Engineering and Light Metals; TBA Research Institute; University of Melbourne; University of South Australia;

Era Eligible

Yes

Journal

Langmuir.