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The kinetics of the structural relaxation process in PHEMA-silica nanocomposites based on an equation for the configurational entropy
C. Théneau1,2, M. Salmerón Sánchez1,3*, J. C. Rodrıguez Hernández1, M. Monleón Pradas1,3, J. M. Saiter2 and J. L. Gómez Ribelles1,3
Center for Biomaterials, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022, Valencia, Spain
2 Laboratoire d'Etude et Caractérisation des Amorphes et des Polymères, Université de Rouen, Rouen, France
3 Centro de Investigación Prıncipe Felipe, Autopista del Saler 16, 46013, Valencia, Spain
* e-mail: email@example.com
Accepted: 2 August 2007
Published online: 17 September 2007
The enthalpy relaxation of polymer-silica nanocomposites prepared by simultaneous polymerization of poly(2-hydroxyethyl methacrylate) (PHEMA) and tetraethyloxysilane, TEOS, a silica precursor, is investigated. Both the glass transition temperature, Tg, and the temperature interval of the glass transition, ΔT g , increase as the silica content in the sample does. Structural relaxation experiments show that the temperature interval in which conformational motions take place broadens as the silica content in the hybrid increases. A phenomenological model based on the evolution of the configurational entropy during the structural relaxation process, the SC model, has been used for determining the temperature dependence of the relaxation times during the process. The results show an increase of the fragility of the polymer as the silica content increases, a feature that can be related to the broadening of the distribution of relaxation times characterized by the β parameter of the stretched exponential distribution. On another hand the silica content increase produces a significant change of the relaxation times in the glassy state.
PACS: 64.70.Pf Glass transitions – / 65.40.Gr Entropy and other thermodynamical quantities – / 81.07.Pr Organic-inorganic hybrid nanostructures –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2007