Control over the interactions between colloidal particles and their (self-)organization at fluid interfaces is of great importance both for fundamental studies and for practical applications. Rendering such systems stimulus-responsive is thus a desired challenge both for investigating dynamic phenomena in two dimensions (2D) and for realizing reconfigurable materials and structures, a hot topic of materials science.
Our recent paper describes the first reversible photocontrol of 2D colloidal crystallization at the air/ water interface, where millimeter-sized assemblies of microparticles can be actuated through the dynamic adsorption/ desorption behavior of a photosensitive surfactant added to the suspension. This allows us to dynamically switch the particle organization between a highly crystalline (under light) and a disordered (in the dark) phase with a fast response time (crystallization in about 10 s, disassembly in about 1 min).
The following video shows the dynamic switching between a disordered particle assembly and a 2D crystal, induced by blue light On/Off cycles. The movie starts when the first light
irradiation starts.
These results evidence a new kind of soft matter system that undergoes (dynamic) dissipative self-assembly: the crystalline state can be maintained only upon energy supply (in the form of light). We anticipate that our concept might be useful for developing macroscopic materials made or mesoscopic building blocks, which can be reconfigured on-demand using a remote, non-invasive and easily shaped stimulus, light.
You can find the paper here.