Glass transition temperature (Tg) is a key parameter in polymers, and we showed that the brittle-tough transition temperature was well correlated to Tg on a very broad Tg range (-30°C < Tg <90°C) (PhD Agustin Rios, 2009-2012). Plasticization mechanisms of polyamides in presence of different kind of molecules (polar, apolar) were studied experimentally in the PhD of Agustin Rios, and results obtained by molecular dynamics (tool developed in the post-doc of Anthony Bocahut) helped to identify plasticization mechanisms and understand how apolar molecules like toluene induced an important Tg drop in PA66. On the basis of these results, original plasticizers structures more efficient in terms of Tg drop were proposed.
- Influence of the sorption of polar and non-polar solvents on the glass transition of Polyamide 6,6 amorphous phase, A. Rios De Anda, L.-A. Fillot, S. Rossi, D. Long, P. Sotta, Polymer Engineering and Science, 2011, 51, 2129-2135.
Sorption of ethanol-toluene-isooctane ternary mixtures in Polyamide 6,6 and induced plasticization effects, A. Rios De Anda, L.A. Fillot, F. M. Preda, S. Rossi, D. Long, P. Sotta, European Polymer Journal 2014, 55, 199-209
We have investigated the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copolymers. Water dynamics was characterized over a wide range of temperatures by dielectric spectroscopy and at microscopic length scales by quasielastic
neutron scattering. The dielectric investigation evidences two relaxations associated with water motions: a fast process corresponding to motions of loosely bonded water molecules and a slower process corresponding to motions of amide−water complexes. While the slower process presents the characteristic Arrhenius temperature dependence of a secondary local relaxation over the whole temperature range, the fast process shows a crossover from Arrhenius to
Vogel−Fulcher−Tamman (VFT) behavior at T ≈ 225 K, characteristic of confined water dynamics. The microscopic investigation by neutron scattering shows than in the VFT regime of the fast process the dynamics present a diffusive nature similar to bulk water. A large distribution of diffusion coefficients indicates possible differences in the connectivity of the hydrogen bond network. Diffusive heterogeneous dynamics can arise from a nonuniform distribution of water. The confinement effect of the polymer matrix is detected as a considerable reduction of the diffusion coefficient of water with respect to bulk. The presence of a crystalline phase results in a slowing down of both the fast and slow processes involving water motions. This could give a hint to the presence of a rigid amorphous phase in the semicrystalline material.
- Dynamics of Water Absorbed in Polyamides, M. Laurati, P. Sotta, D. Long, L. Odoni, A. Arbe, A. Alegria, J. Colmenero, Macromolecules, 2012, 45, 1676-1687