Waterborne Colloidal Polymer/Silica Hybrid Dispersions\nand Their Assembly into Mesoporous Poly(melamine-formaldehyde) Xerogels

Abstract

The acid-catalyzed polycondensation\nof oligo­(melamine-formaldehyde)\nin aqueous phase and in the presence of silica nanoparticles leads\nto a stable dispersion of coexisting silica and polymer nanoparticles.\nThe dispersion can be processed into mesoporous xerogels (<i>S</i>_BET ≈ 200 m² g^–1), whose porosity can be enhanced by etching of silica up to specific\nsurface areas of >400 m² g^–1. The\nformation\nmechanism and the characteristics of the hybrid dispersion are crucial\nto the materials derived from it and analyzed in detail using a variety\nof experimental techniques (electron and force microscopy, light and\nX-ray scattering, ultracentrifugation, and spectroscopy). The transformation\nof the dispersion into xerogels by electrostatic destabilization is\ndescribed. Furthermore, the obtained materials are characterized with\nregard to their porosity and morphology using microscopy and porosimetry.\nThe impact of selected synthesis parameters on the obtained properties\nis discussed, and it was found (most interestingly) that stable porosity\nwas only observed if silica nanoparticles were present within the\ndispersion.