Self-assembly of polymer-grafted inorganic nanoparticles into three-dimensional superlattices

Nanoparticle (NP) superlattice is a fascinating functional material with periodic long-range ordered structure constructed by self-assembly of inorganic NPs. Due to the coupling effect among the NPs, such superlattice assemblies can exhibit excellent collective properties which are distinct from those of individual NPs. The property of superlattice assemblies not only depends on the property of individual NPs and their packing structures, but also relies on the property of ligands on the NP surface. Among various ligands, the polymeric ligands offer advantages to tune the flexibility of superlattices, the packing structure of NPs, the interparticle distance, as well as the interaction softness. By applying different assembly approaches, one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) superlattices of polymer-grafted NPs (PGNPs) have been successfully obtained. Particularly, the 3D superlattices of PGNPs, which have higher degree of order and better structure symmetry, emerge as promising functional materials with desired mechanical, electronic, optical, and magnetic properties. They can find wide applications in many fields, such as information storage, optoelectronic devices, nanomedicine, and catalysis. This review will summarize the recent progress in the self-assembly of PGNPs into 3D superlattice materials in emulsions and solutions. Special attention is focused on the assembly strategies of 3D superlattice materials and the functions of the superstructures. The precise control over the arrangement structure of NPs and the interparticle interactions by tuning the properties of polymer ligands are highlighted. Finally, we will discuss the challenges and future perspectives of superlattices materials of PGNPs.