Inverse Solidification Induced by Active Janus Particles

V. R. Misko, T. Huang, S. Gobeil, X. Wang, F. Nori, J. Schütt, J. Fassbender, G. Cuniberti, D. Makarov, L. Baraban (RIKEN; TU, HZDR-Dresden; VU-Brussels; U-Michigan). Crystals melt and the crystalline long-range order vanishes when thermal excitations or defect concentration in the lattice is sufficiently high. In contrast to this classical scenario, we demonstrate [1] a counter-intuitive occurrence of crystalline long-range order in an initially disordered matrix of passive colloidal particles accommodating chemically active defects - photocatalytic Janus particles (JP). The observed crystallization occurs when the amount of active-defect-induced fluctuations reaches critical value. The driving mechanism behind this unusual behavior resembles a blast-induced solidification. Here the role of "internal micro-blasts" is played by the active defects. The defect-induced solidification occurs under non-equilibrium conditions: the resulting solid exists as long as a constant supply of energy is provided by the catalytic photochemical reaction at the surface of active JP. Our findings could be useful for understanding of the phase transitions of matter under extreme conditions far from thermodynamic equilibrium. [1] T. Huang et al., Adv. Funct. Mater. 2003851 (2020).