Temperature-responsive binary superlattices prepared by the selective solvent evaporation of O/W microemulsion...

Binary nanoparticle superlattices (BNSLs) are one of the important classes of nanomaterial architectures for a wide range of potential applications because they can provide synergistically enhanced properties depending on the morphology and spatial arrangement of nanoparticles (NPs). However, although many studies have been conducted on the fabrication of BNSLs, there are still several challenges in achieving BNSLs with a three-dimensional lattice due to their complicated synthesis, hindering their practical applications. Herein, we report the fabrication of temperature-sensitive BNSLs in complexes of gold nanoparticles (AuNPs), Brij 58 surfactant, and water via a two-step evaporation method. The surfactant was utilized for two different purposes, i.e., surface modification of the AuNPs to control their interfacial energy and as a template material for the formation of the superlattice. Depending on the size and concentration of the AuNPs, the mixture of AuNPs and surfactant self-assembled into three types of BNSLs, including CaF₂, AlB₂, and NaZn₁₃, which were sensitive to temperature. This study is the first demonstration of the temperature- and particle size-dependent control of BNSLs in the bulk state without the covalent functionalization of NPs via a simple two-step solvent evaporation method.