Figure 1: Photo-induced colloidal assembly phenomenon.

(a) PHSA-stabilized PMMA colloids (1.4 μm) at an initial volume fraction of 0.05 are initially dispersed in solution in contact with the ITO-coated glass substrate. (b) A 488 nm laser or UV light source is focused at the objective and scanned across a region of interest. (c) Particle accumulation is observed at the illuminated region. (d–m) Each image pair shows the colloidal structure before and after 60 s of excitation at 488 nm with power density 12 W cm⁻² (d–k) and excitation at 360 nm with power density 0.62 W cm⁻² (l,m). The solvent is CHB/decalin with 50 μM TBAB added (d–i,l,m) or no added TBAB (j,k). In images (d,e,j,k–m), the solution is in contact with an ITO-coated substrate; (f,g) the solution is in contact with a gold coated substrate; h,i is a control experiment in which the solution is in contact with a pure silica substrate. Scale bars, 20 μm.