Relaxation processes in polymers filled with nanoparticles

We report on the influence of filling poly(n-alkyl methacrylates) with 12 nm in diameter Aerosil nanoparticles on relaxation processes and glass transitions, as investigated by dielectric spectroscopy and differential scanning calorimetry. The agglomeration of Aerosil particles in polymer formed a three-dimensional network dividing the polymer into random domains. The filling of polymers with nanoparticles had at least two effects: random field effects imposed by the network and a large particle surface area that imposed an interfacial effect on the polymer. In order to study the role of interfacial effects on the nanoparticle–polymer interface we used two types of Aerosil particles: with hydrophilic and hydrophobic surfaces. We found that the relaxation times of α-relaxation process (sensitive to glass transition) in polymers filled with both hydrophilic and hydrophobic particles were faster than those of bulk polymers measured at the same temperatures. This might be interpreted as reduction of the glass transition temperature in the filled polymers. Semi quantitatively this reduction is in accordance with the Vogel–Fulcher data analysis of the temperature dependencies of the α-process relaxation times. The β-relaxation process was slower for bulk than for filled polymers, but the activation energies of this process were about the same for pure and filled polymers.