Evaluation of porous structure of resorcinol-formaldehyde hydrogels by thermoporometry

The porous structures of resorcinol-formaldehyde (RF) hydrogels were evaluated by thermoporometry (TPM) based on the thermodynamic relationship between the size of the pores and the solidification temperature of the freezable pore water in the pores. Adding the thickness of the nonfreezable pore water layer to the ice crystal size distribution of the freezable pore water calculated from the thermogram (a recording of the heat flux during the solidification of the freezable pore water) allowed for the determination of the porous properties of the RF hydrogels. It was confirmed that the RF hydrogels possess a fairly uniform mesoporous structure formed between the interconnected primary particles, and that the size of the mesopores clearly increased with the increase in the molar ratio of resorcinol to catalyst (R/C) used in the preparation of the initial RF solution. The dependence of both the mesopore volume and the surface area of a given RF hydrogel on the R/C ratio were also established.