Particle formation is rate-limited by the slowest step, the
hydrolysis of the TEOS. The balance between monomer addition
and nucleation determines the size distribution of particles and final
particle size [22–27]. The ratio of hydrolysis rate and condensation
rate directly influence the final particle size and size
distribution. As long as hydrolyzed monomers react much more
quickly than they are produced, monodisperse particles can be obtained
(TE4–TE7 in Table 1, A2–A4 and W3–W5 in Table 3); otherwise,
particles with bimodal distribution and polydispersity will be
achieved (TE1–TE3 in Table 1, A1 and W1, W2 in Table 3). In addition,
according to the result of previous reports [26], the reason for
aggregation includes two aspects: (1) the distance between vibrating
particles; (2) ions concentration. Low concentration of TEOS
and low temperature can increase the average distance between
vibrating particles to avoid the overlapping of double electrical layers
of particles, which benefits the formation of well-dispersedparticles.