title: The kinetics of the structural relaxation process in PHEMA-silica nanocomposites based on an equation for the configurational entropy.
abstract: 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, DeltaTg , 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 beta 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.
authors: Center for Biomaterials, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022, Valencia, Spain.
authors: C
authors: C
authors: Théneau
authors: M
authors: M
authors: Salmerón Sánchez
authors: J C
authors: JC
authors: Rodríguez Hernández
authors: M
authors: M
authors: Monleón Pradas
authors: J M
authors: JM
authors: Saiter
authors: J L
authors: JL
authors: Gómez Ribelles
mesh_terms: D002152:Calorimetry, Differential Scanning; D015392:Chemistry, Inorganic / Q000379:methods; D002625:Chemistry, Organic / Q000379:methods; D019277:Entropy; D005898:Glass; D007700:Kinetics; D015233:Models, Statistical; D053761:Nanocomposites / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods; D011102:Polyhydroxyethyl Methacrylate / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D011108:Polymers; D011102:Polyhydroxyethyl Methacrylate; D012822:Silicon Dioxide