While numerous techniques have been developed to probe interfacial rheology, such methods are riddled with practical difficulties and a lack of understanding of how to interpret the measurements. For dilatational rheology, only methods involving purely spherical interfaces achieve purely dilatational deformation. These analyses commonly assume the Laplace equation describes the pressure jump across the oscillating interface, but this does not account for deviatoric stresses arising when an interface is deformed. Here, we derive the surface stress on an oscillating microscale spherical bubble, accounting for Marangoni and Gibbs stresses, transport, and intrinsic rheology, demonstrating that each behavior contributes separately. We compare several measurement methods, including a microtensiometer that we developed. We show that the measured dilatational modulus can depend on geometry and is not a material property in itself. Thus, interpretation must be undertaken carefully.

Interpreting interfacial dilatational rheology of an oscillating microscale bubble

245th National Meeting (2013)

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