Effect of physical conditioning of pH responsive polyamine nuclei and their subsequent silication

In this work, aqueous solutions of polymeric nuclei based on the polymer polyethyleneimine (PEI), were characterized as a function of pH. The viscosity and zeta potential values of the polymeric solutions were measured and have been related to the degree of protonation of PEI. In addition, the silication of the polymeric nuclei solutions was carried out using trimethoxymethylsilane and the products produced were characterised. The results demonstrate that the zeta potential of the silica particles made with the polymeric nuclei solutions coincides with the zeta potential of the polymeric nuclei solutions themselves, before their silication. Furthermore, a new parameter called the effective ionic strength, I-eff, was defined as the ratio of the ionic strength of the solution to the effective electrostatic nuclei packing. The Ieff values were compared with the silication product results for the different experimental conditions used. For the highest values of pH studied (10-11), silication of the PEI nuclei yielded particles if the effective ionic strength was high, otherwise, gel was formed. In contrast, a decrease in the value of pH to 9 was associated with a regime in which both particles and gel were observed simultaneously. A further decrease in pH (7-8) resulted in no visible reaction. It is expected that the understanding gained from this study should be applicable to other polyamines and silica precursors and therefore this information may be used to predict and control silica growth in general.