Characterization of mesoporous silicas by in situ small angle neutron scattering during isothermal gas adsorption

The recent application of in situ small angle neutron scattering (SANS) mea surements performed during isothermal gas adsorption is a new technique for the characterization of the structure of porous materials. In this techniq ue the coherent scattering length of the condensed gas or vapour is selecte d to match that of the porous solid. This technique is illustrated by inves tigations on two different silica gels, having a highly ordered mesoporous structure. Although both of these gels have a similar nominal 'pore' size o f similar to6 nm, they have a different pore geometry and longer-range text ure. In the first, the gel is produced by a sol-gel process to give a porou s network formed by the packing of monosized sol particles. The second cont ains cylindrical pores which are ordered in a hexagonal array (MCM-41 typo structure). Details of the longer range texture and continuity of these mes oporous materials have been obtained from SANS measurements made in situ wi th contrast matched benzene, adsorbed at 310 K. The results have been analy zed in conjunction with the corresponding adsorption/desorption isotherms w hich have been measured gravimetrically. This in situ SANS technique is sui table for the evaluation of pore texture (network-connectivity, range of st ructural homogeneity) in other mesoporous materials, such as aerogels, as d iscussed. (C) 2001 Elsevier Science B,V. All rights reserved.