Fingering instabilities of a reactive micellar interface.
We present an experimental study of the fingering patterns in a Hele-Shaw cell occurring when a gel-like material forms at the interface between aqueous solutions of a cationic surfactant (cetyltrimethylammonium bromide) and an organic salt (salicylic acid), two solutions known to form a highly elastic wormlike micellar fluid when mixed homogeneously. A variety of fingering instabilities are observed, depending on the velocity of the front (the injection rate), and on which fluid is injected into which. We have found a regime of nonconfined stationary or wavy fingers for which width selection seems to occur without the presence of bounding walls, unlike the Saffman-Taylor experiment. Qualitatively, some of our observations share common mechanisms with instabilities of cooling lava flows or growing biofilms.
W. G. Pritchard Laboratories, Department of Mathematics, Penn State University, University Park, Pennsylvania 16802, USA.
Thomas
T
Podgorski
Michael C
MC
Sostarecz
Sylvain
S
Zorman
Andrew
A
Belmonte