Abstract
Novolac hyperporous materials were successfully synthesized using sol–gel polymerization of Novolacresin with hexamethylenetetramine (HMTA) catalyst in the solvent vapor saturated atmosphere, followed by subcritical drying. Mercury porosimetry results showed that these materials had large pore volume, more than 1 cm3/g. SEM micrographs showed that these materials formed strongly cross-linked aggregates. Therefore, these results demonstrated that these materials would be termed as hyperporous materials. Novolac hyperporous materials can be either crushed or invaded by mercury during mercury porosimetry experiments. In this work, six samples with different initial sol concentration were examined. It has been shown here that a sample with higher porosity exhibited two volume variation mechanisms successively; compaction followed by intrusion, when submitted to mercury porosimetry that real result could be obtained by applying Pirard's collapse model below the pressure of transition, Pt, and Washburn's intrusion theory above Pt. Low porosity sample showed the collapse under mercury pressure only and no transient pressure could be observed. It means mercury does not penetrate the pore network, but the whole material is densified. Microstructure of these hyperporous materials directly influences mechanism changing from collapsing to intrusion.