  The intriguing role of the presence of solutes in the activity of a
self-propelling droplet is investigated. A system of self-propelling micron
sized 4-pentyl-4-biphenylcarbonitrile (5CB) droplets in an aqueous solution of
tetradecyltrimethylammonium bromide (TTAB) as surfactant is considered. It is
shown that addition of glycerol causes the active 5CB droplet to exhibit a
transition from smooth to jittery motion. The motion is found to be independent
of the droplet size and the nematic state of 5CB. Analogous experiments with
Polyacrylamide (PAAm), Polyvinylpyrrolidone (PVP) and Polyvinyl Alcohol (PVA),
as solutes confirm that such a transition cannot merely be explained solely
based on the viscosity or Peclet number of the system. We propose that the
specific nature of physicochemical interactions between the solute and the
droplet interface is at the root of this transition. The experiments show that
the time-scales associated with the influx and redistribution of surfactants at
the interface are altered in the presence of solutes. Glycerol and PVP
significantly enhance the rate of solubilization of the 5CB droplets resulting
in a quicker re-distribution of the adsorbed TTAB molecules on the interface,
causing the droplet to momentarily stop and then restart in an independent
direction. On the other hand, low solubilization rates in the presence of PAAm
and PVA lead to smooth trajectories. Our hypothesis is supported by the time
evolution of droplet size and interfacial velocity measurements in the presence
and absence of solute. Overall, our results provide fundamental insights into
the complex interactions emerging due to the presence of solutes.
