Phase separation of oscillating Ag colloids under intermittent UV illumination. (A) SiO₂-Ag colloids repel each other when light is on, but attract each other when light is off. (B) Clustering process of non-oscillating (top) and oscillating (bottom) Ag particles. Top row: photograph of Ag particles (φ = 7.9%) aggregating in 200 μmol L⁻¹ KCl and 0.25 wt% H₂O₂ aqueous solution. Bottom row: in 200 μmol L⁻¹ KCl and 0.25 wt% H₂O₂ aqueous solution, Ag particles (φ = 8.1%) aggregated upon switching UV on and off at 0.5 Hz (i.e., 1 s light on+1 s light off = one cycle). Note that Cl⁻ is not necessary for the non-oscillating sample to cluster, but was added only to ensure the same solution composition for both samples. (C) Optical micrographs of the phase separation of oscillating Ag colloids (φ = 17%) at a UV trigger frequency of 0.5 Hz (405 nm, ~126 mW cm⁻²) at different time instances.