(15f) Nanoparticles Self-Assembly for the Preparation of Bioinspired Materials with Stimuli-Responsive Color Changing Ability

Octopuses and cuttlefish possess some of the most amazing camouflage abilities of the entire animal kingdom. The core of the camouflage mechanism lies in chromatophores, which are special cells with the ability to displace pigments, located in small pockets in the middle of the cell, over a much larger surface, thus enabling the overall appearance of the cell to change from white or transparent to the specific color of the pigment. Inspired by this mechanism, we have designed color changing polymeric materials exploiting the self-assembly of responsive colloids. The design of the material, unique in its kind, is based on the incorporation of water droplets, generated by microfluidics, in which magnetic nanoclusters are well dispersed, and impart a brown color to the droplets. These droplets play the same role as chromatophores in the octopus’s skin. However, upon exposure to a magnetic field gradient, the clusters rapidly self-organize, align in the direction of the field or accumulate in a small region of the droplet, towards the direction of the strongest magnetic field gradient, thus mimicking the pigment dislocation in the chromatophores. In this manner, the overall color of the droplets changes from dark brown to almost transparent, and leads to macroscopic change in the overall color of the material. To the best of our knowledge, this is the first example of a material with magnetically responsive color change mimicking the pigment dislocation effect.