4(%3)3 - Ecole nationale supérieure de chimie de Montpellier

Figure – 1.10: Self-healing process based on siloxane and alkoxy siloxane systems, a) Composite consisting ofmicroencapsulated catalyst (yellow) and phase-separated healing-agent droplets (white) dispersed in a matrix(green), b) Crack propagates into the matrix releasing the catalyst and healing agent into the crack plane, c) Thecrick is healed by polymerized PDMS, d-e) Scanning electron microscopy images of the fracture surface, showing anempty microcapsule and voids left by the phase-separated healing agent and a smooth surface microcapsule, f)Average maximum load of self-healed vinyl ester by the method and the corresponding healing efficiencies 39 .Moving away from DCPD/Grubbs’ catalyst system due to their associated high cost and loweravailability, in 2006 a new kind of healing system was introduced by Cho et al 39 . This system was basedon the same healing principle as discussed above however the monomers were changed to hydroxylterminatedsiloxanes and alkoxysilanes while catalysts were changed to organotin compounds. Since thiscatalysts were found to be effective only in the presence of water, hence the proposed healing materialwas radical improvement over the DCPD/Grubbs’ system in which the catalyst was highly susceptible tomoisture. Additionally, the liquid phase healing agent, hydroxyl end functionalizedpoly(dimethylsiloxane) & poly(diethoxysiloxane), could be directly mixed with the polymer matix wherethey would remain as phase separated droplets having size between 1 – 20 µm. This left only theorganotin catalyst (di-n-butyltin dilaurate) to be encapsulated along with a solvent (chlorobenzene). Thesize of the microcapsules could be varied from 50 µm – 450 µm by varying the stirring rate during themicrocapsules formation (Figure-1.10) 39 .The reported healingpolymer system along with a bit higher catalyst loading however the observation is obvious given12