NMR dispersion studies of poly(ethylene oxide)/sodium montmorillonite nanocomposites

The frequency dependence of spin–lattice relaxation times measured by means of Fast Field Cycling (FFC) Relaxometry and spin locking on and off-resonance NMR techniques were used to study the molecular dynamics of poly(ethylene oxide) polymer in the confined and bulk phases of PEO/MMT nanocomposite systems. The Rouse model, the renormalized Rouse formalism and the concept of reptation were applied to describe the polymer behavior in the samples studied. The polymer dynamics was found to depend on the molecular weight of the polymer intercalated in the clay structure. Analysis of the NMR T1(ν) profiles allowed discrimination of the molecular dynamics of polymer chains at different locations in the nanocomposite structure.Two components of the T1 spin–lattice relaxation times were indicated for low molecular weight PEO polymers using the FFC method. The longer one was connected with the bulk polymer, whereas the shorter one was attributed to the intercalated polymer fraction. Analysis of the correlation times indicated that polymer confined in montmorillonite galleries is more rigid than that in the bulk phase. To determine the two phases of the polymer for the high molecular weights polymers, additional methods were applied: spin locking, off-resonance NMR techniques and inversion-recovery experiment at a static magnetic field.