posted on 2018-07-30, 00:00authored bySaeed Salimian, Ali Zadhoush, Zahra Talebi, Beatrice Fischer, Peter Winiger, Frank Winnefeld, Shanyu Zhao, Michel Barbezat, Matthias M. Koebel, Wim J. Malfait
Polymer nanocomposites
reinforced with inorganic fillers have sparked
new aerospace, sports goods, automotive, and civil engineering applications.
Here, epoxy nanocomposites with both hydrophobic and hydrophilic silica
aerogel powder fillers are presented. The use of a high porosity,
mesoporous filler such as silica aerogel avoids the typical problems
encountered in dispersing nanoparticles. For both types of aerogel
surface chemistry, the addition of minor amounts of silica aerogel
leads to a strong increase of application relevant properties, e.g.,
fracture toughness and energy, impact strength, Tg, and storage modulus. The strong covalent silica–epoxy
interactions seen for the hydrophilic filler, but absent for the hydrophobic
filler, are reflected in the bulk properties. Detailed fractography
reveals three active toughening mechanisms: (i) an increase in nanoscale
fracture roughness, (ii) crack front bowing and deflection, and (iii)
the formation of shear bands. The industrial availability of silica
aerogel powders, the excellent properties, and the ease of preparation
of the epoxy composites make silica aerogels exceptional nanoporous
fillers for polymer reinforcement.