Manipulation of droplets using the chromocapillary effect: innovative example of the conversion of light energy into mechanical work

The conversion of light energy into mechanical energy is an important issue both for the development of clean vehicles and for selectively acting on micro- and macroscopic systems without mechanical contact. Current technologies always involve storage, transport or transformation intermediaries. Doing without them is a challenge in terms of system size, simplicity and cost. The main existing strategy for a conversion that minimizes the number of intermediate steps is to modify the surface tensions between the object and its environment. It turns out that, at the surface of a liquid, the creation of a surface tension gradient induces material flows (Marangoni effect) capable of setting liquid or solid systems in motion. In particular, these flows can be created and controlled by light, either via thermal effects, or with the aid of light-sensitive surfaces and surfactants (chromocapillary effect).