Shear Effects in Interfacial Rheology and Their Implications on Oscillating Pendant Drop Experiments

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• 作者：Anthony Yeung and Lichun Zhang
• 刊名：Langmuir
• 出版年：2006
• 出版时间：January 17, 2006
• 年：2006
• 卷：22
• 期：2
• 页码：693 - 701
• 全文大小：119K
• 年卷期：v.22,no.2(January 17, 2006)
• ISSN：1520-5827

文摘

Adsorbed molecules that associate or entangle with one another at the fluid interface will give rise to shearingresistance (i.e., resistance to shape change at constant area) on the continuum scale. Where these shear effects occur,familiar theoretical constructs, such as the Young-Laplace equation or the complex dilational modulus, are renderedinvalid. In this work, we report numerical simulations of an oscillating pendant drop with a surface that is a shear-resisting film. Specifically, the drop surface is treated as a Boussinesq fluid (i.e., one that possesses independentviscous coefficients for dilation and shearing). We show that the frequency response of the apparent dilational modulus(based on tensions determined from the Young-Laplace equation) is remarkably consistent with the Maxwell modelof viscoelasticity. It is argued, however, that usage of the Maxwell model, in the context of dilational rheology, isunphysical; as such, the apparent "Maxwellian behavior" is likely due to shear resistance within the Boussinesqmaterial (i.e., the interface may not be undergoing any internal relaxation at all). Our results also predict an apparent"softening" of the adsorbed layer as the interfacial structure becomes more developed.