Fabrication of non-close-packed colloidal monolayers by convective self-assembly using cationic polyelectrolyte-grafted silica particles

Two cationic polyelectrolytes, poly((3-acrylamidopropyl)trimethylammonium chloride) (PAPTAC) and poly(vinylbenzyl trimethylammonium chloride) (PVBTA), have been grafted on the surface of the silica particles, and then these polyelectrolyte-grafted silica particles have been applied to the convective self-assembly (CSA) process using mica substrate to prepare colloidal layers. When the PAPTAC-grafted silica particles (PAPTAC-Si) were used, we obtained the colloidal monolayers with a curious pattern composed of many wiggle beads. By the CSA process using the PVBATA-grafted silica particles (PVBTA-Si), on the other hand, we succeeded in fabricating the colloidal monolayers having a somewhat constant interparticle distance, that is, a non-close-packed (NCP) structure without using any templates. Although both particles have cationic polyelectrolytes on their surfaces, the structures of the resultant colloidal monolayers are quite different from each other, indicating that the molecular structure of the grafted polymer is crucially important for the patterning of the colloidal layers through the CSA process.