Interface-driven soft matter systems : from 2D particle crystallization and light-responsive assemblies to magnet-guided fluid transport

Soft materials interacting at/with liquid interfaces are of great scientific interest because of the multiple weak forces at play that dictate their, often surprising, arrangement and behaviour. In this thesis, we studied novel phenomena and actuating principles for the control of the structure (organization) and dynamics (motion) of soft matter systems at liquid interfaces, from the directed assembly of thousands of solid particles, to the manipulation of small floating drops. We established the first method to both adsorb and crystallise nm- to µm-sized particles at air/water interface, evidencing a new role of surfactants to control two-dimensional (2D) particle organization at extremely low surfactant concentration. We then programmed such 2D assemblies in order to control particle organization with light stimulation, devising two innovative strategies. Using light-absorbing particles allowed us to construct reconfigurable ordered structures (light-controlled inter-particle distance and disassembly). With ordinary particles and photosensitive surfactant, we demonstrated a new kind of dissipative 2D crystals (light-induced organization through continuous consumption of energy). In parallel, we conceived a novel magnetic actuation method for the manipulation of small liquid entities (drops, liquid marbles) by means of deformable paramagnetic liquid substrates, shaping the liquid surface with small permanent magnets and in turn directing the motion of water and oil drops in a user-defined fashion.