  We consider sedimented at a solid wall particles that are immersed in water
containing small additives of photosensitive ionic surfactants. It is shown
that illumination with an appropriate wavelength, a beam intensity profile,
shape and size could lead to a variety of dynamic, both unsteady and
steady-state, configurations of particles. These dynamic, well-controlled and
switchable particle patterns at the wall are due to an emerging
diffusio-osmotic flow that takes its origin in the adjacent to the wall
electrostatic diffuse layer, where the concentration gradients of surfactant
are induced by light. The conventional nonporous particles are passive and can
move only with already generated flow. However, porous colloids actively
participate themselves in the flow generation mechanism at the wall, which also
sets their interactions that can be very long ranged. This light-induced
diffusio-osmosis opens novel avenues to manipulate colloidal particles and
assemble them to various patterns. We show in particular how to create and
split optically the confined regions of particles of tunable size and shape,
where well controlled flow-induced forces on the colloids could result in their
cristalline packing, formation of dilute lattices of well-separated particles,
and other states.
