Curing kinetics and morphology of a nanovesicular epoxy/stearyl-block-poly(ethylene oxide) surfactant system

Abstract

Brittle epoxy based thermosets can be made tougher by introducing structural inhomogeneities at the micro- or nanoscale. In that respect, nano vesicles and worm-like micelles from self-assembling blockcopolymers have been shown to be very effective. This paper describes the curing kinetics and morphology of an epoxy composed of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-methylenedianiline (MDA), modified by 20% of the surfactant stearyl-block-poly(ethylene oxide). Time resolved, synchrotron small-angle X-ray scattering demonstrates that at any time during the epoxy curing process, the surfactant predominantly adopts a bilayer vesicular nano-morphology. Transmission electron microscopy on fully cured systems reveals the coexistence of spherical and worm-like micelles. Differential scanning calorimetry experiments prove that the presence of surfactant reduces the epoxy curing rate but that ultimately full curing is accomplished. The material glass transition temperature falls below that of the pure resin due to plasticization. It is suggested that favorable secondary interactions between the PEO segments and the epoxy resin are responsible for the observed phenomena.

Controlling the generation of bilayer and multilayer vesicles in block copolymer/epoxy blends by a slow photopolymerization process

“…27,28 Few studies have been reported on nanostructured epoxy networks modified with BCP vesicles. 4,[18][19][20][21][29][30][31][32][33] In most cases, vesicular aggregates were formed in the thermoset precursors before curing reaction, and then these were frozen by subsequent formation of the epoxy network. It was demonstrated that, under such conditions, vesicles can only be obtained within a very narrow concentration window.…”