Effect of tetra sulfide groups on self-healing properties of sol-gel coatings

Sol-gel protective coatings draw many attentions since they are low temperature productive, versatile chemically structure and user-friendly. Protective self-healing coatings provide longer life-time and less maintenance and repair s cost via healing the damages autonomically and non-autonomically. In this study, self-healing hybrid sol-gel coatings containing reversible tetra sulfide, synthesized and studied. The effect of the reversible group’s content and the crosslinking density on the thermal, mechanical and healing properties of the developed sol-gel polymers are presented. The prepared hybrid sol-gel polymers exhibited thermal stability in the S-S bond cleavage temperature window and a significant gap closure capability at modest temperatures. Assuming a uniform thickness of the samples, the gap closure efficiency was calculated using the following equation: Gap closure efficiency (%) = (?0− ???0)∗100 The gap closure efficiency of prepared polymer was strongly affected by healing temperature, crosslinking density and content of reversible tetra-sulfide groups. The results presented in Fig. 2 clearly show that when the content of reversible bonds is constant, increasing the rigidity of the network lowers the gap closure efficiency. Nevertheless, the same trend is not applicable when the content of reversible groups is modified. For the samples containing different content of reversible groups, the highest gap closure efficiency does not correspond to the lowest mechanical properties, but it increases as a function of reversible bond content. This suggests that despite the significant effect of the mechanical properties on the healing performance of the hybrid sol-gel films, the controlling factor is the content of reversible bonds (i.e. tetrasulfide groups).Investigation of self-healing hybrid sol-gel showed that regardless of mechanical properties effect on the performance of healing properties, the content of reversible tetra sulfide groups was the main factor in the healing properties.

Keywords:

Corrosion , self-healing , Tetrasulfide , EIS , sol-gel.