Anomalous infrared and visible light absorption by spherical gold nanoparticles dispersed in a comb copolymer

We report the first observations of anomalous infrared and visible light absorption of spherical gold nanoparticles dispersed in a comb copolymer. The dependence of the infrared absorption of the C-O stretch band of the comb copolymer on the volume fraction and size of the gold nanoparticles is measured. Absorption intensities increase when the volume fraction is increased from 0.05 to 0.57 or when the particle size is reduced from 40 to 15 nm. We also show that the experimental transmittances of gold nanoparticles in the visible region are not consistent with a theory of infrared absorption enhancement based on collective electron resonance.