JOURNAL OF CHEMICAL PHYSICS                      VOLUME 119, NUMBER 13                   1 OCTOBER 2003

Stabilization of silver nanoparticles in nonanoic acid: A temperature activated conformation reaction observed with surface enhanced Raman spectroscopy

Dale E. Henneke

Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712

Gokul Malyavanatham

Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712

Desiderio Kovar

Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712

D. T. O’Brien and M. F. Becker

Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712

William T. Nichols and J. W. Ketoa)

Texas Materials Institute and Department of Physics, The University of Texas at Austin, Austin, Texas 78712

Received 8 July 2002; accepted 2 July 2003

Silver nanoparticles were synthesized by ultraviolet ~l5248 nm! laser ablation of an aerosol of micron-sized source particles entrained in nitrogen. As a result of thermionic electron emission and photoionization, nanoparticles produced in this manner were highly charged. The resulting aerosol was primarily composed of nanometer sized particles. The charged nanoparticles were deflected by an electric field that was perpendicular to the aerosol flow. Deflected nanoparticles were deposited directly into n-nonanoic acid flowing along the negative collection electrode. Suspensions of nanoparticles collected in this manner were dark gray in color and were found to be flocculated. When the suspensions were heated to temperatures above 75 °C, a color change from gray to clear was observed. Ultraviolet/visible extinction spectroscopy was performed on each suspension following annealing at different temperatures and times. By modeling the absorption decrease as a first order reaction, a good fit for the data was found. Analysis by dynamic light scattering (DLS) showed that the initial mean flocculent size of the gray suspensions was 602 nm. DLS analysis of the suspensions taken at different annealing intervals showed that the flocculent size decreased, but maintained a narrow size distribution until the size shrank below the instrument resolution limit. The reduction in flocculent size coincided with the observed color change, and an irreversible transition to a deflocculated primary nanoparticle suspension is observed. Surface enhanced Raman scattering is used to confirm that the reaction results from a change in the orientation of the nonanoic molecule on the surface of the nanoparticle.

© 2003 American Institute of Physics.