The role of intraparticle slit pores in porosity development of sodium montmorillonite gels

An intraparticle slit pore model was adapted to provide a physical interpretation of freezing characteristic curves of clay gels. The treatment built on previous descriptive models by incorporating mesoporosity from intraparticle slit pores, which form within walls defining larger capillary pores during hydration. Independent experimental evidence using neutron scattering from thawed pore water in frozen sodium montmorillonite gels revealed complex porosity in the range of 1 to 120 nm which could be attributed to different populations of intraparticle pores including slit pores. Application of the model improved estimation of the micro- and mesopore distributions contributing to water retention in sodium montmorillonite gels, as well as possible dimensions of overlapping slit pores as a function of gravimetric water content. The adsorptive part of the transitional regime for water retention by hydrated Na-Mt gels was restricted to pore widths 2 < w < 10 nm formed by overlapping layers. Capillary processes within this same regime governed water retention in larger pores formed by fabric rearrangement. The proposed model for intraparticle slit mesopores improved fits to the transitional matric potential regime for pore water retention and may prove useful for interpreting water retention curves of Na-Mt obtained by other methods.