  Experiments indicate that microdroplets undergoing micellar solubilization in
the bulk of surfactant solution may excite Marangoni flows and self-propel
spontaneously. Surprisingly, self-propulsion emerges even when the critical
micelle concentration is exceeded and the Marangoni effect should be saturated.
To explain this, we propose a novel model of a dissolving active droplet that
is based on two fundamental assumptions: (a) products of the solubilization may
inhibit surfactant adsorption; (b) solubilization prevents the formation of a
monolayer of surfactant molecules at the droplet interface. We use numerical
simulations and asymptotic methods to demonstrate that our model indeed
features spontaneous droplet self-propulsion. Our key finding is that in the
case of axisymmetric flow and concentration fields, two qualitatively different
types of droplet behavior may be stable for the same values of the physical
parameters: steady self-propulsion and steady symmetric pumping. Although
stability of these steady regimes is not guaranteed in the absence of axial
symmetry, we argue that they will retain their respective stable manifolds in
the phase space of a fully 3D problem.
