Effects of Water on the Interface in a Model Polymer Composite System: A Nuclear Magnetic Resonance Study


The molecular motion of the interfacial material in a model polymer composite was probed and described quantitatively based on deuterium nuclear magnetic resonance (NMR) studies. The system consisted of a silica surface (CabOSil), an aminobutylsilane coupling agent (aminobutysilane-d2, DABS) which was labeled with deuterium in the δ position, and a polymer matrix (bismaleimide, BMI). 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 × 106s-1 for the dry sample, to 4.0 × 106s-1 for the sample incontact with water. For the sample with BMI reacted over it, the jump rate increased from 1.7 × 105s-1 for the dry system to 5.0 × 105s-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 aminobutylilane and D2O. This resulted in the deuteration of the amino group. The motions of the amino group were only slightly faster than those of the labeled methylene segment. Silicon-29 NMR was also used to probe the effects of water. The results were consistent with the breaking of SiOSi bonds and increased mobility at the silicon end of the coupling agent. All systems appeared to return to their original state when the sample was dried. © 1993.



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© 1993 Elsevier, All rights reserved.