Epoxy-based nanocomposites show a high potential for different industrial applications, yet they are rarely studied on a fundamental level. In this work an in-depth comparative investigation of the structure, molecular mobility and vitrification kinetics was performed on three bisphenol A diglycidyl ether (DGEBA)-based materials with different nanofillers: I) halloysite nanotubes (HNTs), II) surface modified halloysite nanotubes (mHNTs), and IIII) taurine-modified layered double hydroxide (T-LDH). The nanofillers are characterized by different interaction with the epoxy matrix and dimensionalities. The methodology comprises X-ray scattering, calorimetry in a static and temperature modulated mode in the form of conventional DSC and fast scanning calorimetry (FSC), as well as broadband dielectric spectroscopy (BDS). The investigations proved an intrinsic spatial structural and dynamic heterogeneity of epoxy-based materials, evidenced by two separate segmental relaxation processes. As expected from the two distinct α-processes, it was shown that, in parallel to the main glass transition, these materials can exhibit an additional low temperature vitrification mechanism. In addition, a competition between the nanoparticle-induced mobilization and immobilization of segmental dynamics was observed. Lastly, the interface between the matrix and the nanoparticles (so-called rigid amorphous fraction) was qualitatively and quantitatively addressed, in dependence of the employed nanofiller structure and its interaction with the matrix.

Spatial inhomogeneity, complex vitrification behavior and interfaces of epoxy and epoxy-based nanocomposites

ACS Spring 2022

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