Structural, thermal and dielectric properties of glycerolized hydrogen-bonded polyvinyl alcohol films

In order to evaluate the influence of plasticizers on the behavior of the dielectric properties of polymers intended for the elaboration of flexible sensors, we have studied the influence of the addition of glycerol (10 wt%-40 wt%) in polyvinyl alcohol (PVA). Once processed, the PVA films were not subjected to any particular annealing and they were dried at room temperature for 24 h before being characterized. This choice allows both to take advantage of the presence of water in the bulk of the material, which will help to make the PVA more flexible (increase of plasticization effect produced by extra-H-bonding) and avoid a transient behavior of water absorption into the material, as we could verify. DSC and FTIR investigations confirm good intermolecular interaction between vinyl polymer chains, glycerol, and water molecules. Dielectric spectroscopy analysis, carried out in [25 & DEG;C-110 & DEG;C] temperature and [0.1 Hz-1 MHz] frequency ranges, reveals a significant increase in the dielectric constant when the glycerol content is higher (at 0.1 Hz: 322 for pure PVA, 1.3 x 10(6) with 40 wt% of glycerol). Polar hydrogen bonds introduced by the glycerol are the main reason for this increase. Ionic conductivity induced by these dipoles dominates the loss tangent response of the material. The activation energy obtained from the DC conductivity plateau obeys to a conventional Arrhenius law with a decreasing value at highest glycerol contents (1.35 eV for pure PVA against 0.46 eV with 40 wt% of glycerol).