(42f) Simultaneous Microscopy and Dilatational Deformation of Complex Fluid-Fluid Interfaces

Particles, amphiphilic molecules, and/or combinations of both that assemble at a fluid-fluid interface influence the stability of an array of bulk materials that are constituted from foams, emulsions, and films. In addition to stability, the mechanical properties of interfaces are relevant to the dynamics of biological membranes, where viscoelastic properties influence the transport of molecules tangentially through the membrane, and mechanical properties provide biological cells with structural integrity. The study of the dynamics and rheology of complex fluid-fluid interfaces is challenging since controlled deformation and simultaneous visualization of a fluid-fluid interface requires highly customized experimental setups. It is also a challenge to perform interfacial deformations that induce purely dilatational deformations, or purely shear deformations, without contributions from the other. We will present data from the investigation of complex fluid-fluid interfaces under purely dilatation deformations utilizing a miniaturized radial Langmuir trough that operates in tandem with a conventional inverted microscope. The equipment and techniques described here are intended to broaden access to simultaneous dilatational-visualization measurements of fluid-fluid interfaces that will advance understanding of structure-property relationships at interfaces, and aid in the development of more complex constitutive equations to describe experimentally observed interfacial rheological behavior.