  We present an experimental investigation of a novel low Reynolds number shear
flow instability triggered by a chemical reaction. An acid-base reaction taking
place at the interface between a Newtonian fluid and Carbopol-940 solution
leads to a strong viscosity stratification, which locally destabilizes the
flow. Our experimental observations are made in the context of a miscible
displacement flow, for which the flow instability promotes local mixing and
subsequently improves the displacement efficiency. The experimental study is
complemented by a simplified normal mode analysis to shed light on the origin
of the instability
