Size effects on the microchemistry and plasticity of Stober silica particles: A study using EFTEM, FESEM, and AFM-SEPM microscopies

Two different samples of monodisperse Stober silica particles were examined using three different microscopies: energy-filtered analytical transmissio n electron microscopy (EFTEM), high-resolution field-emission scanning elec tron microscopy(FESEM), and scanning probe microscopy, in the noncontact at omic force (AFM) and scanning electric potential microscopy (SEPM) modes. U pon drying the silica dispersions, the larger (ca. 141 nm) particles were o nly partially deformed by capillary adhesion, whereas the smaller particles (ca. 36 nm) were strongly deformed and closely packed into dense films of a low porosity, which is evidence of their larger plasticity, or superplast icity. Electric potential distribution maps obtained by SEPM showed a signi ficant interparticle as well as intraparticle contrast, especially in the c ase of the smaller particles. Examination by electron backscattering also r evealed a larger contrast among the smaller particles, thus evidencing a no nuniformity of chemical composition. The results are interpreted considerin g the changes in the synthetic medium and other aspects of the particle gro wth mechanism, and they point toward the possibility of exploiting the plas ticity of the nanosized silica particles in the making of silica monoliths.