PDMS Nanodomains in DGEBA Epoxy Induce High Flexibility and Toughness

ABSTRACT

A nanostructured, highly flexible, and optically transparent epoxy nanocomposite has been formulated reacting diglycidyl ether of bisphenol-A with amine-functionalized silyl-diglycidyl ether-terminated poly(dimethylsiloxane). The concentration of poly(dimethylsiloxane) varied up to 10 wt% and curing was performed at 90°C. Transmission electron microscopy revealed poly(dimethylsiloxane) droplets up to 180 nm in diameter well dispersed in the epoxy. Dynamic mechanical analysis exhibited a decrease in elastic modulus E′ and glass transition temperature T_g, and an increase in the α relaxation strength suggesting increased local molecular motions. Strikingly, poly(dimethylsiloxane) induced a threefold increase in strain at fracture and toughness. Furthermore, hydrophobic behavior was induced by poly(dimethylsiloxane) as the water contact angle increased from 72° (neat epoxy) up to 110° at 5 wt% poly(dimethylsiloxane) content. Fractured surfaces exhibited plastic deformation, contrary to brittleness in the neat epoxy. These nanocomposites are attractive for coatings/encapsulates with improved flexibility, toughness, optical transparency, and water resistance.

GRAPHICAL ABSTRACT

KEYWORDS:

• Epoxy
• microstructure
• nanocomposites
• PDMS
• toughness

Acknowledgments

Adriana Reyes-Mayer was supported by a graduate scholarship from the Mexican Council for Science and Technology, CONACyT. We gratefully acknowledge the technical assistance of Patricia Castillo-Ocampo (Laboratorio de Microscopia Electronica, Metropolitan University-Campus Iztapalapa) with EFTEM. Thanks to L.G. Reyes-Mayer for help with water contact angle measurements.