General Route to Colloidal Nanocrystal Clusters with Precise Hierarchical Control via Star-like Nanoreactors

Abstract

A colloidal nanocrystal cluster (CNC) is a hierarchical nanostructure formed by clustering several nanocrystals into one nano-ensemble, which may exhibit unique optical or catalytic properties different from individual nanocrystals owing to the mutual interactions among neighboring component nanocrystals. However, there is still no universal synthetic route that could be applicable to diverse material compositions with precisely controlled hierarchical structures (i.e., nanocrystal number density, component nanocrystal size, and overall diameter of the CNC) up to now. Herein, a general and novel synthetic strategy was reported for crafting a wide range of inorganic CNCs (i.e., noble metal, semiconductor, and metal oxide) via utilizing amphiphilic star-like poly­(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors prepared by sequential atom transfer radical polymerization. The hierarchical structure of rationally designed CNCs could be readily tailored by varying the P4VP molecular weight of star-like nanoreactors and the parameter optimization during the CNC preparation process, which was inaccessible by conventional synthetic methods.

Precision Synthesis of Ultrastable Hydrophilic Metal Nanocluster Assemblies

“…To further investigate the specific function of thiolate ligands, various amounts of thiolate ligands were utilized to control the synthesis of Au NC assemblies. 51 Without the thiolate ligand, the diameter of single Au nanocrystals inside of the template was about ∼11.6 nm (Figure S10a,b). The diameter of the individual gold nanocrystals reduced from around 5 nm to less than 2 nm as the thiolate ligand (MP:HAuCl 4 ) was increased from 1:1 to 4:1 (Figure 2).…”

“…In this work, with the traditional method to prepare Au NCs, protective thiolate molecules were introduced as the outer ligand, and the domain is restricted to polymer micelles for in situ synthesis, so that ultrasmall Au NCs with stable and well-defined superstructure assemblies can be prepared. To further investigate the specific function of thiolate ligands, various amounts of thiolate ligands were utilized to control the synthesis of Au NC assemblies . Without the thiolate ligand, the diameter of single Au nanocrystals inside of the template was about ∼11.6 nm (Figure S10a,b).…”

Silver Nanocrystal Array with Precise Control via Star-like Copolymer Nanoreactors

“…In contrast to nanoetching technology, the template-based nanofabrication method had the advantages of low cost, and various templates could be used to prepare the high-density nanocrystal array. − Liner block copolymers (BCPs) containing two or more chemically diverse polymer segments were usually used to fabricate the nanocrystal array with distinct well-defined nanostructures because of their spontaneous assembly ability. − However, the liner BCP method with dynamic instability was particularly affected by environmental variations, such as temperature, pH value, solvent polarity, salt concentration, ionic strength, and so on. − Therefore, to solve these issues, it was necessary to develop a robust approach to fabricate nanocrystal array with precise control and structural stability. Star-like polymers as unimolecular nanoreactors exhibited highly regular structures and unique properties owing to the spatially defined yet compact architecture and controlled components and sizes. − Diverse functional nanocrystals such as metal oxides, semiconductors, and metals could be obtained by choosing various precursors and subsequent growth conditions. , With this unimolecular nanoreactor method, Ag nanocrystal arrays with uniform nanoscale sizes and nanoscale gap distances over a large area could be used in immunoassays, biosensing, and other fields, − whose huge electromagnetic (EM) field localization coupled with surface plasmon resonance denoted as surface-enhanced Raman scattering (SERS) results in outstanding properties. − Compared to the conventional nanoreactor approaches based on linear BCPs, the star-like BCPs covalently linked by a molecule could form stable unimolecular micelles which served as nanoreactors in various types of solvent and at different pH values and temperatures. − …”