Building nanopolymers: lessons from polymer physics and chemistry
Organized arrays of inorganic nanoparticles show electronic, optical, and magnetic properties that originate from the coupling of size- and shape-dependent properties of individual nanoparticles (NPs). Self-organization of NPs in a controllable, well-defined manner is an efficient strategy for producing nanostructures with hierarchical architectures, and potentially, building functional materials by a bottom-top approach. Currently, a quantitative prediction of the structure of nanoparticle ensembles and of the kinetics of their formation remains a challenge.
We developed two new paradigms for the self-assembly of metal NPs. One of the approaches utilized a striking analogy between amphiphilic ABA triblock copolymers and hydrophilic metal nanorods end-tethered with hydrophobic polymer chains. We assembled the nanorods in structures with varying morphologies and properties. The self-assembly process was rationalized and mapped by using phase-like diagrams.
In the second approach, we exploited a marked similarity between the self-assembly of nanoparticles and step-growth polymerization. In this approach, the nanoparticles acted as multifunctional monomer units (nanomers), which formed reversible, noncovalent bonds at specific bond angles and organized themselves into a supramolecular colloidal polymer (nanopolymer). We show that the kinetics and statistics of step-growth polymerization enable a quantitative prediction of the architecture of linear, branched, and cyclic self-assembled nanostructures; their aggregation numbers and size distribution; and the formation of structural isomers. Building on this similarity, we proposed the concept of colloidal chain stoppers.
The proposed strategies provide a route to the quantitatively predicted organization of nanoparticles in supracolloidal assemblies with new properties.