Nanosphere-microsphere assembly: Methods for core-shell materials preparation

Core-shell composite materials consisting of a silica core and a polystyrene (PS) shell were prepared by colloidal assembly of PS nanospheres onto silica microspheres. The assembly process was controlled by specific chemical (amine-aldehyde) or biochemical (avidin-biotin) interactions between the nanospheres and microspheres. Colloidal assembly was performed using polymer nanoparticles (100-200 mo diameter) and silica particles (3-10 mum diameter). Heating the assembled materials to temperatures above the glass transition (T-g) of the polymer nanoparticles allows the polymer to flow over the microsphere surfaces, resulting in uniform core-shell materials. Nanosphere packing density on the microsphere surfaces influenced the uniformity of the resulting polymer shell. Scanning electron microscopy, transmission electron microscopy, scanning force microscopy, and Fourier transform infrared spectroscopy were used to characterize the materials presented in this paper.