[Effect of cation surfactants on absorption spectra of silver nanoparticle in liquid phase]

Yellow Ag nanoparticles, with diameter of 20 nm, exhibit a resonance absorption peak at 400 nm. After adding some cation surfactants (CS), the absorbance at 400 nm becomes weak, (namely, there exists hypochromic effect), but the absorbance at wavelengths longer than 400 nm is enhanced and shows a red shift. When adding concentration of CS, the absorbance at wavelengths longer than 400 nm becomes weak again, the peak at 400 nm is enhanced (namely, there exists hyperchromic effect) and the absorption peaks show a blue shift. The results showed that this is caused by the strong hydrophobic force and electrostatic force between the CS and silver nanoparticls, which results in a change in the silver nanoparticle shape.