Relaxation Processes in PVAc-HA Nanocomposites

Fundamental principles of polymer physics were used for description of relaxation behavior of polymer chain near solid surface. In a nanocomposite, considerable portion of polymer matrix is in contact with the filler surface even at very low filler loadings. In this study, nanocomposite was considered as a two component system consisting of (i)bulk polymer matrix and (ii)effective particles composed of adsorbed polymer shell and filler particle core. Both polymer phases, i.e., bulk and immobilized, are able to relax, however, each of them on a different time scale. Thus, above the neat matrix Tg, these two phases undergo (i)free and (ii)retarded reptation dynamics due to the adsorption processes on the filler surface, respectively. Relaxation time was calculated for each phase using the reptation theory. To calculate the mixed response of the whole polymer nanocomposite, a simple rule of mixtures model and percolation model were used. Calculated composite elaxation times were correlated with experimental modulus recovery data measured after the Payne effect in poly(vinylacetate)-hydroxyapatite nanocomposite. Good agreement was found between theoretical predictions and experimental data.