Effects of Water on the Interface in a Model Composite System: An NMR Study

摘要

The molecular motion of the interfacial material in a model polymer composite hasbeen probed and quantitatively described based on deuterium NMR studies. The system consisted of a silica surface (Cab-O-Sil), an aminobutylsilane coupling agent (aminobutylsilane-d2, DABS) which was labelled with deuterium in the beta position, and a polymer matrix (bismaleimide). the addition of water to the system increased the molecular mobility of the surface-bound coupling agent. The motions of the coupling agent adsorbed on amorphous silica were simulated using a two-site jump model with tetrahedral jumps. For the coupling agent at the air interface, jump rates increased from 1.0 x 10 to the 6th power s-1 for the dry sample, to 4.0 x 10 to the 6th power s-1 for the sample in contact with water. For the sample with BMI reacted over it, the jump rate increased from 1.7 x 10 to the 5th power s-1 for the dry system to 5.0 x 10 to the 5th power s-1 for the wet system. The motional rate increase for both systems was a factor on the order of 3-4 with the addition of water. Deuterium exchange experiments were conducted between adsorbed aminobutylsilane and D20. This resulted in the deuteration of the amino-group. The motions of the amino group were only slightly faster than those of the labelled methylene segment. Silicon-29 NMR was used to probe the effects of water. The results were consistent with the breaking of Si-O-Si bonds and increased mobility at the Si end of the coupling agent AH systems appeared to returned to their original state when the sample was dried.