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

Core-shell composite materials consisting of a silica core and a polystyren e (PS) shell were prepared by colloidal assembly of PS nanospheres onto sil ica microspheres. The assembly process was controlled by specific chemical (amine-aldehyde) or biochemical (avidin-biotin) interactions between the na nospheres 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 transiti on (T-g) of the polymer nanoparticles allows the polymer to flow over the m icrosphere surfaces, resulting in uniform core-shell materials. Nanosphere packing density on the microsphere surfaces influenced the uniformity of th e resulting polymer shell. Scanning electron microscopy, transmission elect ron microscopy, scanning force microscopy, and Fourier transform infrared s pectroscopy were used to characterize the materials presented in this paper .