Hybrid Ultrathin Gold Nanowire Gels: Formation and Mechanical Properties

This report is about the chemical formation of gels from ultrathin gold nanowires (AuNWs) and the gels' properties. An excess of triphenylphosphine (PPh₃) initiated the gelation of AuNWs with core diameters below 2 nm and an oleylamine (OAm) ligand shell dispersed in cyclohexane. The ligand exchange of OAm by PPh₃ changes the AuNW-solvent interactions and leads to phase separation of the solvent to form a macroscopic gel. Small angle X-ray scattering and transmission electron microscopy indicate that hexagonal bundles in the original dispersion are dispersed, and the released nanowires entangle. Rheological analyses indicate that the resulting gel is stabilized both by physical entanglement and crosslinking of AuNWs by Van der Waals and π-π interactions. Chemically formed AuNW gels have solid-like properties and crosslinks that distinguish them from highly concentrated non-crosslinked AuNW dispersions. The AuNW gel properties can be tuned via the Au:PPh₃ ratio, where smaller ratios led to stiffer gels with higher storage moduli.