Unwinding of poly(ethylene oxide) chains grafted an silica under a shear flow of cyclohexane, observed by spin-labelling

Poly(ethylene oxide) chains of molecular weight 2000 have been grafted on pyrogenic silica, spin-labelled at their free end and put into contact with cyclohexane, The electron paramagnetic resonance of the nitroxide free radical gives evidence of two specific environments: namely, trains adsorbed on the solid with a restricted motion and loops and tails protruding into solution with a high mobility. The dynamic parameters such as the rotational correlation time and the static ones such as the fraction of each population have been evaluated. Under a flow of solvent the unwinding of the chains has been observed with increasing flow rate in our experimental range. Some mechanisms are proposed to explain this behaviour.