Nanoporous silica gels with well-defined textural properties have been used to calibrate the thermoporosimetry technique with various aromatic solvents including o-, m-, and p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene. The calibration has been validated on a test alumina sample, and the results are in good agreement with the one derived from gas sorption. The data obtained for the three xylene isomers indicate a linear variation of T p, the temperature of crystallization of the solvent inside the pore of size R p, with T 0, the normal crystallization temperature (T p = aT 0 + b). A linear fit of these curves gives a constant value for the slope (a ≈ 1), but the value of the intercept b depends strongly on the size of the pore. These fitting curves describe perfectly the behavior of the other solvents showing that extrapolation within a structure-related family of solvents is possible. The expression b = −196.41/R p is derived from the data collected for the xylene isomers, and the final expression T p = 1.02T 0 − 196.41/R p can be used directly to predict the crystallization temperature of any solvent in a pore of size R p. This general law is derived for benzene-substituted solvents. Nevertheless, this work provides the first evidence of a possible predictive use of thermoporosimetry without fastidious preliminary calibration. The solvents studied in this paper are particularly valuable for swelling of polyolefins.

The solvents o-, m-, p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene were calibrated as condensates used in the thermoporosimetry technique. Exponential relationships were found connecting the pore radii R(p) (in nm) and the freezing-point depression of the swelling solvent deltaT (in degrees C) on the one hand and the apparent energy of crystallization W(a) (in J cm(-3)) and deltaT on the other hand: R(p) = t exp[-1/(c deltaT)]; W(a) = W0 exp(deltaT/f). Pore- or mesh-size distributions can be derived from differential scanning calorimetry results by using the following equation: dV(p)/dR(p) = k{[cY(T)deltaT2]/[W(a)R(p)]}. All the numerical parameters were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or gamma-rays, were submitted to thermoporosimetry study. Relative mesh-size distributions, which depend on the polymer/solvent pair, were calculated for these polyolefins with o-, m-, and p-xylene as solvent and were found to be in the same sequence as those of their degrees of swelling and the irradiation doses received.