Microfluidic Production of Mechanochromic Photonic Fibers Containing Nonclose-Packed Colloidal Arrays.

Photonic fibers are important raw materials for structurally colored fabrics. In particular, the mechanochromic fibers potentially provide color-tunable clothes, like chameleon skins. Herein, microfluidic jetting to continuously produce mechanochromic fibers in a controlled manner is used. The jet is produced by flow-focusing the photocurable dispersions in a surfactant-laden carrier fluid using microfluidic devices. The dispersions contain monodispersed silica particles in an elastomer-forming resin. As the silica particles have repulsive interparticle potential in the resin, they spontaneously organize into a nonclose-packed regular array, developing structural colors. The jet of the dispersions is photocured in situ by irradiation of ultraviolet at the exit of the microfluidic channel, continuously producing the photonic fibers. As the interparticle separation among silica particles is shortened along the radial direction by stretching the elastic fibers, the structural colors are dynamically blue shifted. Also, the original colors are reversibly recovered by relaxing the fibers as the deformation is fully elastic. The nonclose-packed array of inelastic silica particles provides a wide range of color tuning and high reversibility. Moreover, microfluidic jetting enables the production of Janus fibers composed of two distinct color domains, which enriches the available structural colors through color mixing.