Nanopore effects on the combustion temperature of resorcinol-formaldehyde xerogels

The rationalization of thermal analysis data of porous substances is often complicated by the fact that it is not always possible to synthesise non-porous reference samples. Therefore, it is difficult to quantify the effect that the porosity has on the thermal behaviour. Here, we present detailed investigations about the thermal behaviour of a mesoporous model system consisting of a resorcinol-formaldehyde xemgel, synthesised via an acid-catalysed route. Samples were prepared with different pore sizes varied over the entire nanoscale range (from <10 nm up to similar to 1 mu m), without affecting the composition of the xemgel. This allowed a systematic investigation of the thermal behaviour, which is purely dependent on the porosity. Thermogravimetric analysis of this model system revealed a pronounced increase in combustion temperature and decrease in combustion rate for samples with mean pore diameters smaller than 20 nm. Interestingly, this finding can be correlated with the Knudsen regime of the diffusion of oxygen.