Extending the range of liquids available for NMR cryoporometry studies of porous materials

Nuclear magnetic resonance (NMR) cryoporometry, although well established, can be limited by the inability of any one liquid to probe a broad range of pore sizes, a relatively small number of commonly-used probe liquids and the requirement to match the probe liquid to the chemistry of the material being studied. Here we demonstrate, for the first time, the use of menthol and t-butanol as probe liquids in NMR cryoporometry measurements. Using appropriate estimates for the values of the melting point depression constant, k_c, and the non-freezing surface layer, 2sl, NMR melting data was converted into pore size distributions. The melting point depression constant for t-butanol is similar to that of cyclohexane; however due to its functionality, t-butanol may be the preferred liquid used to study the porosity of hydrophilic materials. Menthol, having a larger value of k_c, can accurately analyze larger pore sizes up to 100 nm. This represents the first use of menthol and t-butanol to accurately probe pore dimensions in NMR cryoporometry.