Heat conduction in nano-environment observed in cooling processes of colloidal silver nanoparticles in water

Ultrafast dynamics of colloidal silver nanoparticles in an aqueous solution was investigated by observing the ultrafast lensing effects caused by a ph oto-induced refractive index change. The ultrafast response consisted of an instantaneous peak by the optical Kerr effect and a subsequent bi-exponent ial decay component. The decay component was independent of the relative po larization planes of pump and probe beams and had temperature-dependent tim e constants ranging from 0.4 to 2.2ps and from 10 to 100 ps. A minimum at a round 7 degrees C was found for the time constant of the fast component. Th e results suggest that the structure of water molecules adjacent to the sil ver surface is affected by hydrogen bonds in a temperature-dependent manner similar to that of the molecular structure of bulk water.