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 aspect ratios (length/diameter) were prepared using the template synthesis approach. After template synthesis, the nanorods were freed from the template membrane and dispersed in either hexafluoro-2-propanol (HFIP) or CHCl3. The stability of these nanorod sols was monitored using visible absorption spectroscopy. For both the Au and Ag nanorods (in both solvents), sols prepared 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 stabilizers poly(vinylpyridine) or poly(vinylpyrrolidone) did not enhance the stability of these nanorod sols. In addition to these studies of sol stability, UV-vis absorption spectroscopy was used to investigate the plasmon absorption band of these sols. The wavelength of maximum absorbance of the plasmon 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-shifted relative to analogous sols prepared in HFIP.