(543i) A Miniaturized, Radial Langmuir Trough for Simultaneous Visualization and Dilatational Deformation of a Complex Fluid-Fluid Interface

The viscoelastic properties of monolayers of amphiphilic molecules at a fluid-fluid interface determine, in part, the stability of the foams and emulsions found in cosmetics, pharmaceutical formulations, foodstuffs, and petroleum refining. In addition to foam and emulsion stability, the mechanical properties of fluid-fluid interfaces are relevant to the study of biological membranes, especially lipid bilayers, where viscoelastic properties affect the transport of molecules tangentially through the membrane, and mechanical properties provide biological cells with requisite structural integrity. Unlike most bulk fluids, fluid-fluid interfaces are highly compressible and display a rich variety of viscoelastic behavior that depend on the area-density of the interfacial molecules. As a consequence of compressibility, a complete rheological description requires measurements of both shear and dilatational properties; thus, interfacial rheological devices are typically designed to generate either pure shear deformations, or pure dilatational deformations. However, isolating purely dilatational deformations in a geometry amenable to simultaneous direct visualization of the interfacial structure, e.g. with fluorescence microscopy, has always been an experimental challenge. We present a novel design, and data from, a miniaturized radial Langmuir trough that generates purely dilatational deformations with a 9:1 compression ratio, and operates on the platform of a conventional fluorescence microscope. This equipment, which was produced almost entirely from basic additive manufacturing techniques, is intended to broaden access to simultaneous dilatation-visualization measurements that otherwise require specialized assemblies.