Surface area investigation of materials with transition layers of continuously changing electron density

Abstract

The paper examines the comparison of the surface areas of siliceous materials with the surface polymer layer, measured by means of SAXS and BET methods. The investigated materials possessed the transition layer at the air–surface polymer layer interface border in which the electron density changes in a continuous manner. The results show that the equation [ I( q)= k 1/ q+ k 2/ q 3] gives SAXS surface areas comparable with those from BET measurements. However, the former are lower. In addition, the difference between them depends on the transition layer thickness, as well as on the composition of the surface polymer layer. In case of the surface area investigation of rigid materials with soft surface polymer layer and not sharply defined interface border, the SAXS method seems to be more convenient than the BET one due to the low temperature (−196°C) during BET measurements.