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

Two types of chemically modified silica gels with covalently bonded hydroph obic (alkyl, SiO2-C-8) and hydrophilic (aminoalkyl, SiO2-NH2 groups were st udied by dielectric relaxation method. For SiO2-C-8 two relaxation maxima w ere detected at 140 and 238K. From comparison with bulk silica the lower te mperature maximum was assigned to cooperative re-orientation of residual si lanols 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 alc ohol and so it was assigned to mobility of orientation defects in mono-dime nsional 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.