Self‐Assembly of Binary Mixed Homopolymer Brush‐Grafted Silica Nanoparticles

Abstract

Covalently grafting polymer chains onto inorganic nanoparticles (NPs) with a sufficiently high grafting density (i.e. polymer brushes) is an effective way to combine the desired properties of core NPs (e.g. optical, electrical, and magnetic properties) with those of polymers (e.g. flexibility, processability, and environmental responsiveness). Binary mixed homopolymer brush-grafted NPs (MBNPs) refer to those grafted randomly or alternately with two types of chemically dissimilar homopolymer chains. They are not only “multifaceted” (i.e. incorporated with multiple functionalities) but also “smart” (i.e. stimuli-responsive). As predicted by theoretical studies and computer simulations, MBNPs can exhibit a variety of intriguing self-assembled morphologies, leading to a unique class of “patchy” NPs with a well-controlled distribution of two polymers on the NP surface. These nanostructures in turn will influence the hierarchical self-assembly of MBNPs into metamaterials at a larger length scale. In this book chapter, we review our recent progress in the study of self-assembly of the well-defined MBNPs prepared by a two-step surface-initiated reversible deactivation radical polymerization method from asymmetric difunctional initiator-functionalized silica particles. When the silica core NPs are larger than the polymer chain dimensions, the situation is reminiscent of mixed brushes grafted on a flat substrate. When the silica NP sizes are similar to the polymer chain dimensions, many ordered nanostructures can be obtained. In addition to the self-assembled nanostructures of MBNPs from solvent casting, their self-assembly in good and selective solvents and homopolymer matrices is also reviewed. Finally, future research direction is pointed out for the hierarchical self-assembly of MBNPs.