Study of cooperative effects of silanols on modified silica by dielectric relaxation method

摘要

Two types of chemically modified silica gels with covalently bonded hydrophobic (alkyl, SiO2-C-8) and hydrophilic (aminoalkyl, SiO2-NH2 groups were studied by dielectric relaxation method. For SiO2-C-8 two relaxation maxima were detected at 140 and 238K. From comparison with bulk silica the lower temperature maximum was assigned to cooperative re-orientation of residual silanols and higher one to melting of physically adsorbed water. Both maxima are much weaker for SiO2-C-8 then for bulk silica. In Arrhenius coordinates relaxation at 238K exhibits similar behavior as OH groups in polyvinyl alcohol and so it was assigned to mobility of orientation defects in mono-dimensional chain of physically adsorbed water. For SiO2-NH2 no low temperature relaxation effect was observed. Intensive relaxation was measured at 248 K only. Strong interaction between supramolecules of silanol groups, bonded aminogroups and adsorbed water was assumed. [References: 5]