On the healing mechanism of sol-gel derived hybrid materials containing dynamic di-sulfide bonds

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Sol-gel technology is increasingly being used in coatings for corrosion protection and adhesion improvement. So far, the self-healing concept in sol-gel coatings has only been approached from extrinsic healing perspective (i.e. use of nano and micro carriers of corrosion inhibitors) [1]. Despite the benefits of this approach, the damaged area remains open to ambient environment. The implementation of intrinsic healing approaches in sol-gel coatings can thus very well complement current extrinsic ones in order to offer more extended corrosion protection. In the present work the intrinsic healing sol-gel hybrid systems containing dynamic disulfide bonds were developed. The ability of developed systems to restore their cohesion at three different temperatures was evaluated, revealing 70oC as the optimum healing temperature. In order to get a better understanding of the healing mechanisms, dynamic mechanical thermal analysis (DMTA) was complemented by in-situ raman spectroscopy to follow the evolution of the di-sulfide bonds during the healing cycles. Mechanical properties and content of the broken dynamic bonds were found to be the key parameters in the healing performance of the developed systems. Faster healing kinetics at 70oC disclosed the dominating role of the breaking/re-joining of the dynamic di-sulfide bonds in the healing mechanism.