21.4 Conclusions Microcapsules containing magnetic nanoparticles were synthesized and incorporated into self-healing epoxy specimens for fracture testing. The microcapsules were successfully guided to the intended fracture location using magnetic fields. SEM of the fracture surface showed an estimated apparent volume fraction of 4.1 % for controls and 43 % for guided specimens both at 4 % microcapsule nominal weight percent. Specimens containing guided microcapsules displayed an increase in fracture toughness over control specimens when low weight percentages of microcapsules were used (less than 3 % by weight). At higher microcapsule weight percentages, guided specimens showed a transition to non-linear fracture as opposed to the brittle fracture exhibited by control specimens. These same trends were observed as nanoparticle concentration was increased within the microcapsules at fixed microcapsules weight percentages. Successful self-healing was achieved in guided specimens, with a potential increase in performance over controls. Acknowledgment The work presented in this paper was supported by an NSF Grant (CMMI 1351760). References 1. Trask, R.S., Bond, I.P., Williams, G.J., Williams, H.R.: Bioinspired self-healing of advanced composite materials. Collection of Technical Papers—AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, ISSN: 02734508 (2008) 2. Caruso, M.M., Blaiszik, B.J., White, S.R., Sottos, N.R., Moore, J.S.: Full recovery of fracture toughness using a nontoxic solvent-based healing system. Adv. Funct. Mater. 18, 1898–1904 (2008) 3. Rule, J.D., Sottos, N.R., White, S.R.: Effect of microcapsule size on the performance of self-healing polymers. Polymer 48, 3520–3529 (2007) 4. Brown, E.N., Kessler, M.R., Sottos, N.R., White, S.R.: In situ poly(urea-formaldehyde) microencapsulation of dicyclopentadiene. J. Microencapsul. 20(6), 719–730 (2003) 5. Caruso, M.M., Blaiszik, B.J., Jin, H., Schelkopf, S.R., Stradley, D.S., Sottos, N.R., Moore, J.S.: Robust, double-walled microcapsules for selfhealing polymeric materials. ACS Appl. Mater. Interfaces 2(4), 1195–1199 (2010) 6. Kang, S., Baginska, M., White, S.R., Sottos, N.R.: Core-shell polymeric microcapsules with superior thermal and solvent stability. ACS Appl. Mater. Interfaces 7(20), 10952–10956 (2015) 7. Brown, E.N., White, S.R., Sottos, N.R.: Microcapsule induced toughening in a self-healing polymer composite. J. Mater. Sci. 39, 1703–1710 (2004) 8. Laurent, S., Saei, A.A., Behzadi, S., Panahifar, A., Mahmoudi, M.: Superparamagnetic iron oxide nanoparticles for delivery of therapeutic agents: opportunities and challenges. Expert Opin. Drug Delivery 11(9), 1449–1470 (2014) 9. Zhao, Y., Fang, J., Wang, H., Wang, X., Lin, T.: Magnetic liquid marbles: manipulation of liquid droplets using highly hydrophobic Fe3O4 nanoparticles. Adv. Mater. 22, 707–710 (2010) Fig. 21.9 Healing tests for a guided specimen with 2 % microcapsules by weight (left) and a control specimen with nominal 5 % microcapsules byweight (right) 21 Controlled Placement of Microcapsules in Polymeric Materials 183
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