Adaptive Shape Ripening and Interparticle Bridging of L-Arginine-Stabilized Silica Nanoparticles During Evaporative Colloidal Crystal Assembly.

During evaporative self-assembly of colloidal crystal films, spherical L-arginine-stabilized silica colloids adapt to different close-packed geometries by faceting and forming bridge connections with their nearest neighbors. We systematically studied the morphological changes of 37 and 138 nm diameter colloids during evaporative assembly and compared them to 65 nm Stöber silica colloids prepared without L-arginine. Colloidal crystal films were grown from particles that had been dialyzed against water or L-arginine, and tetraethylorthosilicate (TEOS) and/or L-arginine were added to solutions during colloidal film growth. Solid-state 29 Si NMR spectra showed the presence of L-arginine and incompletely condensed silica in colloids grown from silica seeds in L-arginine solutions. These colloids were especially susceptible to chemical ripening during the colloidal assembly process, adopting faceted shapes that increased the packing density of the colloidal crystal films. The addition of L-arginine and TEOS accelerated these shape changes by catalyzing the hydrolysis and olation of silica, and by adding a source of silica to the solution, respectively. This chemistry provides a route to single-component and binary colloidal crystals crystals composed of non-spherical silica building blocks.