THE EFFECT OF PRESSURE ON THE SURFACE-PLASMON ABSORPTION-SPECTRA OF COLLOIDAL GOLD AND SILVER PARTICLES

The first measurements of the effect of pressure on the peak position (ωsp) and line width (fwhm) of the surface plasmon absorption in several Au and Ag hydrosols have been recorded up to 10 kbar. Red shifts of the plasmon peak with increasing pressure are observed for relatively large metal particles prepared by the citrate procedure (Au, [inlineformulaomitted] = 265 Å; Ag, [inlineformulaomitted] = 230 Å). The shift for silver is over twice that of gold (–420 cm–1 vs –200 cm–1). These red shifts are interpreted in terms of pressure-induced volume changes within the context of a free-electron model. In contrast, particles prepared by the Faraday method (Au, [inlineformulaomitted] = 54 Å; Ag, [inlineformulaomitted] = 60 Å) show initial blue shifts with pressure, with the magnitude again larger for silver. Upon aging (as well as upon heating in the case of Au), the Au and Ag Faraday sols exhibit an increase in their average particle size and degree of aggregation. Correspondingly, the pressure response of their plasmon absorption approaches that of the citrate sols. © 1990, American Chemical Society. All rights reserved.