Determination of Interfacial Rheological Properties Through Microgravity Oscillations of Bubbles and Drops

by National Aeronautics and Space Administration

This report summarizes our derivations of analytical expressions for the frequencies and damping constants for small-amplitude axisymmetric shape oscillations of a liquid drop suspended in an immiscible fluid host in microgravity. In particular, this work addresses large Reynolds number shape oscillations and focuses on the surface rheological effects that arise from the presence of insoluble surfactants at the interface. Parameters characterizing viscous effects from the bulk phases, surface viscous effects, Marangoni effects from the surface advection and diffusion of surfactants, and the Gibbs elasticity are all considered and analyzed to determine the relative importance of each contribution. Supplementing the analytical treatment for small-amplitude oscillations, a numerical boundary integral equation formulation is developed for the study of large-amplittide axisymmetric oscillations of a drop in vacuum. The boundary integral formulation is an extension of classical potential flow theory and approximately accounts for viscous effects in the bulk fluid as well as the surface viscous and Marangoni effects resulting from an insoluble surfactant contaminating the interface. Theoretical and numerical results are presented for four distinct cases. These, range from the case when the effects of the surfactants are 'negligible' to 'large' when compared to the viscous effects in the bulk phases. The feasibility of the non-contact measurement of the surface parameters, using experimental observations for the oscillation frequencies and damping constants of drops and bubbles, is discussed.Nadim, Ali and Rush, Brian M.Glenn Research CenterBUBBLES; DROPS (LIQUIDS); MICROGRAVITY; OSCILLATIONS; RHEOLOGY; MARANGONI CONVECTION; VISCOUS FLOW; REYNOLDS NUMBER; INTEGRAL EQUATIONS

70 pages, Paperback

Published May 30, 2018

About the author

The National Aeronautics and Space Administration (NASA) is an independent agency of the U.S. federal government responsible for the civil space program, aeronautics research, and space research.