Scaling laws for the critical rupture thickness of common thin films

Coons, J. E. and Halley, P. J. and McGlashan, S. A. and Tran-Cong, T. (2005) Scaling laws for the critical rupture thickness of common thin films. Colloids and Surfaces A: Physicochemical Engineering Aspects, 263 (1-3). pp. 258-266. ISSN 0927-7757

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Abstract

[Abstract]: Despite decades of experimental and theoretical investigation on thin films, considerable uncertainty exists in the prediction of their critical rupture thickness. According to the spontaneous rupture mechanism, common thin films become unstable when capillary waves at the interfaces begin to grow. In a horizontal film with symmetry at the midplane, unstable waves from adjacent interfaces grow towards the center of the film. As the film drains and becomes thinner, unstable waves osculate and cause the film to rupture. Uncertainty stems from a number of sources including the theories used to predict film drainage and corrugation growth dynamics. In the early studies, the linear stability of small amplitude waves was investigated in the context of the quasi-static approximation in which the dynamics of wave growth and film thinning are separated. The zeroth order wave growth equation of Vrij predicts faster wave growth rates than the first order equation derived by Sharma and Ruckenstein. It has been demonstrated in an accompanying paper that film drainage rates and times measured by numerous investigations are bounded by the predictions of the Reynolds equation and the more recent theory of Manev, Tsekov, and Radoev. Solutions to combinations of these equations yield simple scaling laws which should bound the critical rupture thickness of foam and emulsion films. In this paper, critical thickness measurements reported in the literature are compared to predictions from the bounding scaling equations and it is shown that the retarded Hamaker constants derived from approximate Lifshitz theory underestimate the critical thickness of foam and emulsion films. The non-retarded Hamaker constant more adequately bounds the critical thickness measurements over the entire range of film radii reported in the literature. This result reinforces observations made by other independent researchers that interfacial interactions in flexible liquid films are not adequately represented by the retarded Hamaker constant obtained from Lifshitz theory and that the interactions become significant at much greater separations than previously thought.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Deposited in accordance with the copyright policy of the publisher.
Depositing User: epEditor USQ
Faculty / Department / School: Historic - Faculty of Engineering and Surveying - No Department
Date Deposited: 11 Oct 2007 00:19
Last Modified: 02 Jul 2013 22:31
Uncontrolled Keywords: thin films, thinning velocity, critical film thickness, spontaneous rupture mechanism, scaling laws, Lifshitz theory
Fields of Research (FOR2008): 09 Engineering > 0904 Chemical Engineering > 090499 Chemical Engineering not elsewhere classified
Identification Number or DOI: doi: 10.1016/j.colsurfa.2005.01.008
URI: http://eprints.usq.edu.au/id/eprint/316

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