Molecular mobility and interfacial polarization study on model two-phase epoxy-amine networks
Résumé
Maxwell-Wagner-Sillars (MWS) polarization is observed when performing BDS measurements on polymer-based composite materials, or semicrystalline polymers. Although its origin is clearly ascribed to the interface between two phases with distinct dielectric properties [1], it is often difficult to extract valuable information about the studied material from the analysis of this dielectric phenomenon. To this end, model heterogeneous polymer networks have been developed which satisfy most of the assumptions of Wagner's model [2]: spherical inclusions constituting a minority phase in a continuous matrix, with perfect adhesion. Cross-linked epoxy-amine microgels (CEMs) were synthesized by precipitation polymerization [3], in the form of spheres about 6 µm in diameter. The CEMs were then dispersed in an epoxy-amine matrix of similar chemical nature, resulting after curing in a network exhibiting topological cross-linking heterogeneity which can be fine tuned by adjusting the crosslinking degree of each of phase. This cross-linking heterogeneity induces a contrast in dielectric properties, giving rise to MWS polarization. BDS was used to study molecular mobility of the two phases (matrix and inclusions) and MWS polarization in this model heterogeneous material. Wagner’s model and two sets of data inputs (either mean ε' and σ' values or raw experimental spectra) were used to model the theoretical MWS polarization and compare it with the experimental one. The good agreement obtained between Wagner's historical model and experiment on a real heterogeneous system provides a better understanding of the parameters that govern MWS polarization and hints at links with the physico-chemical structure of the heterogeneous material. References [1] P.A.M. Steeman, J. van Turnhout, Dielectric Properties of Inhomogeneous Media, in: F. Kremer, A. Schönhals (Eds.), Broadband Dielectr. Spectrosc., Springer Berlin Heidelberg, 2003: pp. 495–522. [2] K.W. Wagner, Erklärung der dielektrischen Nachwirkungsvorgänge auf Grund Maxwellscher Vorstellungen, Arch. Für Elektrotechnik. 2 (1914) 371–387 [3] M.-L. Michon, Heterogeneous epoxy-amine networks from the dispersion of cross-linked polymer microparticles, PhD thesis (INSA Lyon), 2014