Three-dimensional condensation on a spherical nanoscale seed was simulated by classical molecular dynamics. In order to observe the effects of the dimension of seeds and thermodynamic conditions on the condensation characteristics, initial seed size and system supersaturation ratio were the factors that were examined. At supersaturation ratios above the critical value, two stages of nucleation were found to exist within the system, where the first stage is from the seed growth and the second from homogeneous nucleation. Therefore, the growth and homogeneous nucleation characteristics were each decomposed and analyzed separately. The Yasuoka-Matsumoto method was used to calculate the nucleation and growth rate. The homogeneous nucleation characteristics coincided with the classical nucleation theory. The condensation characteristics, however, showed a discrepancy with the modified classical nucleation theory for completely wetted heterogeneous nucleation, where no supersaturation ratio influence could be observed. The seed size was found to have a reciprocal effect on the growth rate, but showed to be insignificant on the homogeneous nucleation characteristics for this system. The critical nucleus size from kinetic analysis showed a greater difference compared to the first nucleation theorem, classical nucleation theory, or free energy analysis. All in all, the classical nucleation theory showed relatively good agreement compared to previous homogeneous nucleation studies by molecular dynamics, but a modification was found to be necessary when applying to heterogeneous growth of nanoparticles.
© 2011 American Chemical Society