2.3. Fabrication of Cr60@Polyurea-GNP Microcapsules

For the emulsions containing GNP in the Cr60 wax capsules, GNP was mixed with Cr60 initially following the same procedure as preparation of Cr60 capsules. Moreover, emulsions are stirred after sonification for 3 h in a double walled reactor since they tend to sediment over time. It was noticed that the reaction time of half an hour at 80 °C is not sufficient to fully complete the interfacial reaction since the sedimented particles formed a non-redispersible solid. However, increasing reaction time to three hours, gave the possibility to easily redisperse the dispersion. Two different concentrations of GNP were prepared, separately. A schematic view of the chemical interfacial reaction and structure of the prepared capsules can be seen in Figure 1a.

(a) Scheme of chemical interfacial reaction and structure of the prepared capsules; (b) from left to right Crodatherm60@polyurea-0.1%GNP, 0.1%GNP, Crodatherm60@polyurea-0.04%GNP, 0.04%GNP, Crodatherm60@polyurea.