High-pressure effects on nanometric hybrid xerogels, p-phenylenediamine/silica and p-anisidine/silica

The hybrid xerogels p-phenylenediamine/silica and p-anisidine/silica were prepared with different surface areas and porosities and they were processed at high pressure (7.7 GPa or ∼76000 atm) in a quasi-hydrostatic medium at room temperature. The morphologies of the materials were studied before and after the high-pressure treatment by using N₂ adsorption–desorption isotherms, scanning electron microscopy and infrared thermal analysis. The porous hybrid p-phenylenediamine /silica presented after the high-pressure treatment a surface-area reduction and an entrapment of organics in closed pores. However, the less porous hybrid p-anisidine /silica showed a surprising behavior, a pressure-induced increase in surface area with opening of pores. We propose a mechanism based on the inhibition of the cold sintering process by the organics to explain these results. PACS 81.20.-n; 81.40.Vw; 81.05.-t