Block-copolymer-like Self-assembly Behavior Of Mobile-ligand Grafted Ultra-small Nanoparticles

Incorporating nanoparticles(NPs)into polymers is an efficient way to fabricate functional materials with new structures.As a new type of self-assembly unit,polymergrafted NPs exhibit unique self-assembly behaviors leading to the formations of fascinating ordered structures.Therefore,studying the structure and self-assembly behavior of polymer-grafted NPs has become a hot topic in recent years.We use coarsegrained(CG)molecular dynamics simulations to study the self-assembly behavior of polyoxometalate(POM)nanoparticles(NPs)decorated with mobile polymer ligands in bulk state.We demonstrate that due to the mobile nature of the grafted ligands on NP surface,NPs have the ability to expose part of their surfaces,leading to a blockcopolymer-like self-assembly behavior.The exposed NP surface serves as one block and the grafted ligand polymers as another.The system has a strong ability to selfassemble into long-range ordered structures as block copolymers due to large incompatibility between POM and ligand polymers,i.e.,POM NPs can form lamellae,cylinder,and sphere structures,which are consistent with previous experimental results.More importantly,these ordered structures are on the sub-10-nm scale,which is demanding for many applications.At low graft density,we find a new inverse-cylinder structure formation where polymers form cylinders and POMs form a continuous network structure.A full self-assembly phase diagram is constructed which illustrates rules to manipulate the self-assembly structures of NPs decorated with mobile polymer ligands.By mixing purely nanoparticles grafted with mobile polymer ligands and homopolymers,we have obtained a continuous phase structure similar to a block copolymer that has not been obtained before.We hope these computational results will be useful for the new design of nanostructures with improved optical or electronic functions.