Adsorption properties of silica towards poly(ethylene oxide) as a functionof pH studied by spin-labelling

Poly(ethylene oxide) chains spin labelled at their free end were adsorbed o n amorphous silica and put into contact with buffers of different pH. The E lectron Paramagnetic Resonance spectrum has a shape very sensitive to the B rownian motion of the free radical and exhibits composite lines characteris tic of two environments: loops and tails protruding into solution with a fa st motion; trains adsorbed on the solid surface with a restricted motion. B oth components were analysed and the rotational correlation times and the t wo populations of labels were plotted as a function of pH and temperature. The chains are progressively desorbed as both increase due to the weaker hy drogen bounding with the reactive silanol groups present at the surface. Th erefore a molecular picture of the chains at the interface can be gained.