Preparation and stability of template-synthesized metal nanorod sols in organic solvents

Gold and silver nanorods of diameter 40 and 90 nm and having a variety of a spect ratios (length/diameter) were prepared using the template synthesis a pproach. After template synthesis, the nanorods were freed from the templat e membrane and dispersed in either hexafluoro-2-propanol (HFIP) or CHCl3. T he stability of these nanorod sols was monitored using visible absorption s pectroscopy. For both the Au and Ag nanorods (in both solvents), sols prepa red from the 90-nm diameter nanorods were found to be less stable than sols prepared from the 40-nm diameter nanorods. The addition of the polymeric s tabilizers poly(vinylpyridine) or poly(vinylpyrrolidone) did not enhance th e stability of these nanorod sols. In addition to these studies of sol stab ility, UV-vis absorption spectroscopy was used to investigate the plasmon a bsorption band of these sols. The wavelength of maximum absorbance of the p lasmon resonance band (lambda(max)) for both Ag and Au sols was shifted to higher wavelengths when the nanorod diameter was increased from 40 to 90 nm . In addition, the lambda(max) values for sols prepared in CHCl3 were red-s hifted relative to analogous sols prepared in HFIP.