Variation in viscous fingering pattern morphology due to surfactant-mediated interfacial recognition events

The study of the formation of finger-like patterns during displacement of a viscous fluid by a less viscous one is of technological importance. The mo rphology of the viscous-finger patterns generated is a function of many par ameters such as the flow rate, difference in viscosities of the two fluids and the interfacial tension. We demonstrate herein that the morphology of p atterns formed during viscous fingering in a Hele-Shaw cell during displace ment of paraffin oil by aqueous solutions of the surfactant sodium dodecyl sulphate (SDS), is extremely sensitive to interfacial tension variation bro ught about by complexation of divalent cations with the surfactant SDS. The variation in morphology of the patterns formed has been quantified by meas uring the fractal dimensions of structures formed in a radial Hele-Shaw cel l as well as the average finger width in a linear Hele-Shaw cell. This tech nique shows promise for studying other interfacial phenomena in chemistry s uch as biorecognition as well as dynamic processes occurring at interfaces.