Facile fabrication of free-standing microtubes composed of colloidal spheres

Free-standing microtubes with diameters of 250-300 nm composed of polystyrene microspheres were fabricated by a facile self-assembly approach templated with porous alumina membranes. A polycation (polyethyleneimine, PEI) layer was deposited onto the surfaces of the alumina membrane channels to change the surface charge from negative to positive, and polystyrene microspheres whose surface was modified with carboxyl groups were subsequently immobilized onto the channel walls in basic solution through electrostatic interaction. Successive annealing of the sample was carried out to make the adjacent polystyrene microspheres coalesce slightly, and after dissolving the alumina membrane, freestanding latex microtubes were obtained.