Robust and Eco-Friendly Waterborne Phase-Change Composite Protective Coatings Containing Paraffin-Loaded SiO2/Fe3O4 Hybrid Wall Microcapsules and Their Application in Long-Term Effective Temperature Regulation of the Protected Substrate

SiO2/Fe3O4 hybrid wall microcapsules containing a paraffin core were successfully fabricated by Pickering emulsion template self-assembly and sol–gel technologies. The walls of these microcapsules were embedded with different dosages of Fe3O4 nanoparticles due to the effect of Fe3O4 Pickering emulsion of different concentrations. The resultant microcapsules exhibited a regular spherical morphology and a rough outer surface compared with that of the SiO2 wall. Thermal analysis indicated that the encapsulation efficiency (Een), thermal energy-storage efficiency (Ees), and thermal conductivity of paraffin@SiO2/Fe3O4 hybrid wall microcapsules prepared with 0.01 mol/L Fe3O4 Pickering emulsion [Pa@SiO2/Fe3O4-Ms (0.01)] increased by 16.71%, 16.88%, and 28.4% compared with those of paraffin@SiO2 microcapsules (Pa@SiO2-Ms), respectively. The phase-change temperatures and enthalpy of Pa@SiO2/Fe3O4-Ms (0.01) with an 80–100 μm particle size range changed little after 300 thermal cycles. At the same time, these microcapsules were introduced into water-based acrylic resin paint to prepare phase-change composite protective coatings (PCCPCs) and exhibited excellent thermoregulatory performance. The real-time temperature difference and temperature ramp rate of PCCPCs incorporating 5 wt % (80–100 μm) Pa@SiO2/Fe3O4-Ms (0.01) increased by 4.6 °C and decreased by 2.45 °C/min compared to that of the pure coating, respectively. Meanwhile, the fluctuation amplitude and fluctuation frequency of the average temperature on the back side of 5 wt % (80–100 μm) Pa@SiO2/Fe3O4-Ms (0.01)-PCCPCs decreased by 3.8 °C and extended by 395 s compared to that of the pure coating under one heating and cooling cycle, respectively. This study will provide great potential applications for addressing the risk of shrinkage deformation and cracking of the protected concrete substrates under high-frequency and large temperature difference conditions.