Chemically driven nonlinear waves and oscillations at an oil-water interface

An experimental investigation is presented of chemically driven dynamic instability of an oil-water interface in a cylindrical and annular glass container. The immiscible liquids are water containing a surfactant (TSAC) and nitrobenzene containing iodine. The reaction at the interface leads to complex deformation patterns including rotating solitary waves, multiple wave trains, periodic and nonperiodic oscillations, source-to-sink propagation, and intermittent behavior. A phase diagram is established for the two solute concentrations ranging from 10^-4 to 10^-1 M. It shows five distinct regions of different dynamic regimes, determined by interaction of at least three mechanisms: dynamic wetting of the container wall, capillary effect, and Marangoni instability of the liquid-liquid interface. The influences of aspect ratio, concentration product, and temperature are investigated and local time traces are derived from electropotential differences. Their spectral analysis reveals details of periodic or irregular motion. Transitions between the dynamic modes of the system during its temporal evolution are recorded. Quantitatively determined profiles of regular waves are analyzed by exponential functions and a simple model for this is proposed.