Restricted relaxation in polymer nanocomposites near the glass transition

The relaxation behavior of organically modified layered silicate-epoxy nanocomposites was studied using a combination of standard and temperature-modulated differential scanning calorimetry. For such nanocomposites, the silicate layers were intercalated in the matrix resin and epoxy networks were grafted onto the silicate layer surfaces. Enthalpy recovery that occurred during physical aging was used as a probe to detect restricted relaxation behavior in the nanocomposites. Addition of the intercalated nanoparticles resulted in a slower overall relaxation rate and a wider distribution of relaxation times. The nanocomposites also showed a higher glass transition temperature compared to that of the unreinforced resin. To explain the observed results, a domain relaxation model was proposed that included three possible relaxation modes. On the basis of this model, the restricted relaxation arising from intercalated and exfoliated layered silicates can be understood.