ABSTRACT
Magnetically guided microcapsules are used to achieve self-healing with 1/10th of the healing components required using traditional self-healing approaches. Microcapsules are rendered responsive to magnetic fields by suspending magnetic nanoparticles in the core material. The nanoparticles are surface-modified to enable urea-formaldehyde encapsulation within a phenyl acetate core. Magnetic fields are used to guide the microcapsules to the expected fracture location in tapered double-cantilever beam (TDCB) epoxy specimens. This guiding method achieves an order of magnitude increase in local microcapsule concentration over controls, resulting in successful self-healing at microcapsule concentrations as low as 0.025 wt %. Additionally, the observed healing is both more consistent and significantly higher than that of control specimens, remaining relatively constant across all weight percentages tested.
ABSTRACT
Strong polymer-silica aerogel composites were prepared by chemical vapor deposition of cyanoacrylate monomers onto amine-modified aerogels. Amine-modified silica aerogels were prepared by copolymerizing small amounts of (aminopropyl)triethoxysilane with tetraethoxysilane. After silation of the aminated gels with hexamethyldisilazane, they were dried as aerogels using supercritical carbon dioxide processing. The resulting aerogels had only the amine groups as initiators for the cyanoacrylate polymerizations, resulting in cyanoacrylate macromolecules that were higher in molecular weight than those observed with unmodified silica and that were covalently attached to the silica surface. Starting with aminated silica aerogels that were 0.075 g/cm(3) density, composite aerogels were made with densities up to 0.220 g/cm(3) and up to 31 times stronger (flexural strength) than the precursor aerogel and about 2.3 times stronger than an unmodified silica aerogel of the same density.
