Novel photoresponsive core-shell microcapsules for Karstedt catalyst: Double-layer silicone wax microcapsules coated with polydopamine

To improve the compatibility, photothermal responsiveness, and batch stability of Karstedt catalyst microcapsules, Karstedt/silicone wax/PDA microcapsules were prepared by a melt-dispersion method combined with in-situ PDA coating. In this system, silicone wax served as a double-layer wall material, while PDA acted as a photothermal layer. The morphology, structure, thermal stability, photothermal behavior, catalyst release, curing kinetics, and mechanical properties were characterized by SEM, FTIR, TGA, DSC, ICP-OES, infrared thermal imaging, and tensile testing. The prepared microcapsules showed regular morphology, relatively uniform particle-size distribution, and good coating integrity, with a photothermal conversion efficiency of 25.39%, stable photothermal response after five heating/cooling cycles, and a room-temperature latency period exceeding 30 days. The microcapsules exhibited a two-stage release behavior, namely slow Pt accumulation followed by accelerated release, which was attributed to the temperature-induced softening/melting of the silicone wax shell and reduced diffusion resistance. The curing kinetics conformed to an autocatalytic model. Compared with neat Karstedt-cured silicone rubber, the silicone rubber cured with Karstedt/silicone wax/PDA microcapsules showed an increase in elongation at break from 252.31% to 287.81%, while the tensile strength decreased from 0.465 to 0.310 MPa. This work provides a simplified strategy for preparing latent photothermally responsive Karstedt catalyst microcapsules for light-controlled curing of silicone rubber.