Oleylamine Impurities Regulate Temperature-Dependent Hierarchical Assembly of Ultranarrow Gold Nanowires on Biotemplated Interfaces

Nanocrystals are often synthesized using technical grade reagents such as oleylamine (OLAm), which contains a blend of 9-cis-octadeceneamine with trans-unsaturated and saturated amines. Here, we show that gold nanowires (AuNWs) synthesized with OLAm ligands undergo thermal transitions in interfacial assembly (ribbon vs. nematic); transition temperatures vary widely with the batch of OLAm used for synthesis. Mass spectra reveal that higher-temperature AuNW assembly transitions are correlated with an increased abundance of trans and saturated chains in certain blends. DSC thermograms show that both pure (synthesized) and technical-grade OLAm have primary melting transitions near -5 degrees C (20-30 degrees C lower than the literature melting temperature range of OLAm). A second, broader melting transition (in the previous reported melting range) appears in technical grade blends; its temperature varies with the abundance of trans and saturated chains. Our findings illustrate that, similar to biological membranes, blends of alkyl chains can be used to generate mesoscopic hierarchical nanocrystal assembly, particularly at interfaces that further modulate transition temperatures.