Study by 1H NMR of the Influence of the Porosity and Solvent on the Conformations of Macromolecules at an Interface: Poly(Ethylene Oxide) Grafted on Silica

The ¹H NMR technique was used to study the behaviour of poly(ethylene oxide) chains grafted chemically on silica. A noticeable influence of the nature of the surface and solvent on the conformation of the grafted macromolecules was observed. For precipitated silica the chains adopted a disordered conformation whereas for pyrogenic silica they formed a more uniform layer. The grafting ratio and the solvent can both modify the conformations of the chains. The dependence of the relaxation times (T₁ and T₂) on the grafting ratios is discussed qualitatively from a phenomenological point of view. Different models are proposed for the two extreme grafting ratio levels in both the absence and the presence of solvent. Without solvent, for both grafting ratios, the macromolecules lie very flat on the silica and the layer is more organized, especially at high grafting ratio. In the presence of solvent the chains spread out in the solvent, adopt a more extended conformation and the local concentration of monomers at the surface decreases.