Controllable dielectric and electrical performance of polymer composites with novel core/shell-structured conductive particles through biomimetic method

Novel silica/poly(dopamine)/silver (from inner to outer) (denoted as SiO₂/PDA/Ag) conductive micro-particles were first synthesized by biomimetic poly(dopamine) coating. These micro-particles were then coated with a poly(dopamine) layer to form core/shell-structured particles, with silica/poly(dopamine)/silver core and poly(dopamine) shell (denoted as SiO ₂/PDA/Ag/PDA). This multilayer core/shell micro-particles were confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscope. Polymer composites were then prepared by mechanical blending of poly(dimethyl siloxane) and the core/shell-structured particles. It was found that the silver layer and the poly(dopamine) shell had good adhesion with substrate and they kept intact even under violent shearing stress during mechanical mixing. The effect of the thickness of outermost poly(dopamine) shell as well as the loading amount of this filler on the dielectric and electrical properties of the composites was further studied. The results showed that the dielectric constant, dielectric loss, and conductivity of the composites decreased with increasing shell thickness (10-53 nm) at the same loading level. And the maximal dielectric constant of composites was achieved in the composites filled with SiO ₂/PDA/Ag/PDA (with 10-15 nm PDA shell) particles, which was much larger than that of the composite filled with SiO₂/PDA/Ag particles without insulative PDA shell. At the same time, the composites can change from conductor into insulator by controlling the shell thickness of core/shell-structured conductive particles. This simple and controllable biomimetic method may be applied to construct many other conductive filler in order to realize controllable dielectric and electrical performance of polymer composites.