Photo-Controlled two-dimensional soft materials from microgel particles at liquid interfaces
Microgels are valuable building blocks both for investigating colloidal phase transitions and for the fabrication of complex materials that react and adapt to external stimuli. In particular, liquid interfaces are perfect two-dimensional (2D) templates for microgel assembly because of the long-range ordered organization that can be achieved in a fast and reliable manner. The structure of microgel assemblies at liquid interfaces can be precisely controlled by changing external parameters (e.g, temperature, pH, surface pressure). The microgels volume and compressibility can be modulated, in turn affecting their mutual interactions and final organization. The goal of this multidisciplinary proposal is to develop novel systems where light actuation can be coupled in to control microgel properties at liquid interfaces. Up to now, the external stimuli used to control 2D microgel assemblies had several limitations: the lack of spatial resolution, a poor control over the response time, and the irreversibility of the transitions. With the proposed systems, an optical trigger will allow the external control of the inter-particle interactions as well as of the particle size and compressibility with exceptional spatial and temporal resolution. Two synthetic routes are considered: i) covalent modification of the microgel structure with the addition of light-responsive co-monomers; ii) mixing of microgels with photoresponsive surfactants. Different responses are offered by these two strategies. In the former case, unprecedented local control over microgel assemblies can be achieved, opening the way to novel studies over 2D phase transitions. In the latter case, a composite system is proposed, where microgel properties, as well as macroscopic surface flows, can be manipulated by light actuation. Ultimately, reconfigurable colloidal structures endowed with multiple properties that can be advantageously switched in a fast and local manner by the external stimulation are envisioned.