Dilational Viscoelasticity of Adsorption Layers Measured by Drop and Bubble Profile Analysis: Reason for Different Results

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• 作者：V. B. Fainerman ; V. I. Kovalchuk ; E. V. Aksenenko ; R. Miller
• 刊名：Langmuir
• 出版年：2016
• 出版时间：June 7, 2016
• 年：2016
• 卷：32
• 期：22
• 页码：5500-5509
• 全文大小：568K
• 年卷期：0
• ISSN：1520-5827

文摘

The dilational viscoelasticity of adsorption layer was measured at different frequencies of drop and bubble surface area oscillations for aqueous C₁₂EO₅ solutions. The modulus values obtained by the two experimental protocols are the same for Π < 15 mN/m, while for higher surface pressures the values from drop experiments exceed those from bubble profile analysis. The nature of this phenomenon was studied using stress deformation experiments. At high surfactant concentrations the magnitude of surface tension variations is essentially higher for drops as compared with bubbles, leading to an increased viscoelasticity modulus for oscillating drops. The observed effects are analyzed quantitatively using a diffusion controlled exchange of matter model. The viscoelasticity moduli for a number of surfactants (different C_nEO_m and Tritons, C₁₃DMPO, and SDS) are reported, and it is shown that the discrepancies between the data obtained by the two methods for many surfactants agree well with the predictions made here.