Extracting the pore size distribution of compliant materials from nitrogenadsorption

Adsorption of nitrogen at 77.4 K is a well-established technique for the ch aracterization of mesopores. However, this method has been questioned in th e case of compliant materials, as the capillary pressures upon sorption can be as large as several MPa's and thus high deformations are expected upon analysis. Simultaneous recording of nitrogen sorption data and linear lengt h changes for silica aerogels, a class of highly porous, compliant material s, reveals a new type of isotherm, that is characteristic for compliant mat erials in general. Comparison of dilatation and sorption data shows that th e bulk modulus of a compliant material can be calculated from its nitrogen sorption isotherm alone. Using this information together with a model that describes the relationship between macroscopic deformation and changes in p ore size and volume, the isotherm can be corrected for the contraction of t he sample during analysis. The corresponding pore size distribution is foun d to be in excellent agreement with results deduced from small angle X-ray scattering. (C) 2001 Elsevier Science B.V. All rights reserved.