The E n was observed to be negatively dependent on the number of moles of TEOS; with increasing number of moles, there was a decrease in E n . Similar behaviour was observed for NH 4 OH. An interaction between the number of moles of NH 4 OH and the number of fractionated additions of TEOS was identified. As discussed for the shell thickness, the fractionated addition of TEOS term was also included in the model, due to the presence in the interaction term, despite not exhibiting a significant effect itself (p-value = 0.821). Monodisperse populations were achieved at higher numbers of moles and more additions, while the inverse produced populations classified as near-monodisperse. These relationships are summarised in Equation 3 and the contour maps presented in Fig. . It is of interest to note that the terms active in effecting E n were also active in influencing t shell . This is due to the commonality between the mechanism, outlined in the previous section; namely that the number of moles of NH 4 OH influences the size of the micelle formed and is used to hydrolyse TEOS. Using fractionated additions of TEOS influences the silica shell growth or the formation of silica by-product. By controlling the micelle size (where shell growth occurs) and rate of hydrolysis of TEOS, it is possible to create monodisperse particles; as showcased by the interaction of number of moles of NH 4 OH and fractionated additions of TEOS. Monodispersity of particle population is vital in the consideration of such materials for biomedical applications and hence this observation is important, as it clearly demonstrates how both the size and dispersity of particles can be carefully controlled through manipulation of experimental conditions.