Fabrication of Depth-Controlled Dimples on Polymer Microsphere and Capturing of Nano-Sized Objects

Polymer microspheres containing submicron-sized surface dimples were prepared through the acid-dissolving removal of silica nanoparticles as templates from the surface of core-shell microspheres, which were prepared by modified suspension polymerization of a silica nanoparticle-dispersed polymerizable monomer mixture (methyl methacrylate and divinylbenzene dispersing). We demonstrated depth control of the dimples on the surface of polymer microspheres and evaluated their capturing properties. The depth of the dimples could be facilely controlled by changing the surface polarity of silica nanoparticles (1µm) as templates during the synthesis of the core-shell microspheres. The depth of the prepared dimples ranged from 250 to 810nm, and the gate diameter of the dimple was related to its depth owing to the spherical shape of the template. The inner surfaces of the dimples were evaluated based on the adsorption of cationic and anionic fluorescent dyes. Confocal laser microscopy observations indicated that the inner surfaces of the dimples were densely stained with both fluorescent dyes, whereas the outer surfaces of the microspheres were not stained, suggesting that the inner surfaces of the dimples were more hydrophobic. Silica particles smaller than the gate diameter of the dimple were crammed (or jammed) into the inner space of the dimple, and the captured silica particles did not drop off even after washing with water more than five times. Because the larger silica nanoparticles could not be trapped, the dimples could selectively capture the nanosized objects in their inner space.