Surface tension and fingering of miscible interfaces

Experiments on miscible, buoyantly unstable reaction-diffusion fronts and non-reacting displacement fronts in Hele-Shaw cells show a fingering-type instability whose wavelengths (λ) are consistent with an interfacial tension (Σ) caused by the change in chemical composition, even though the solutions are miscible in all proportions. The relation Σ ≈ K/τ , where τ is the interface thickness and K ≈ 4 ± 2 x 10 dyne, enables prediction of our measured λ and results from many prior experiments. These results indicate that even for miscible fluids, surface tension is generally more significant than diffusion in interfacial stability and flow characteristics. PACS classifications: 47.20.Ma, 05.70.Np, 68.10.Cr Address correspondence to: Paul Ronney Department of Aerospace and Mechanical Engineering University of Southern California OHE 430J Los Angeles, CA 90089-1453 (213) 740-0490 (213) 740-8071 (fax) [email protected] Revised version submitted to Physical Review Letters, March 2000