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The localization of the rubber vulcanization reaction close to the silica filler surface was investigated in isoprene rubber composites (IR NCs): the main goal was to highlight the role of curing agents' dispersion and filler surface features on the spatial propagation of the rubber cross-links and the resulting mechanical behavior of the material. The study was realized by tailoring the morphology of the curing activator, i.e. by vulcanizing IR NCs with Zn@SiO 2 double function filler, composed of Zn(II) single sites anchored on SiO 2 filler, in comparison to silica filled IR NCs vulcanized with microcrystalline ZnO. The microscopic cross-links distribution was measured by Transmission Electron Microscopy for network visualization (NVTEM) and Time Domain Nuclear Magnetic Resonance (TD-NMR). Besides the NCs mechanical behavior was characterized both at small strain and at fracture. In the presence of Zn@SiO 2 , higher cross-link density in proximity to SiO 2 particles was evidenced, which gradually spreads from the filler surface to the bulk, induced by localization of the Zn(II) centers. IR NCs with Zn@SiO 2 resulted stiffer (+45%) and with a lower fracture toughness (less than one third), compared to m-ZnO based NCs, which shows a quite homogeneous structure of the rubber cross-links network. The results highlighted the correlation between the composites structural features and their macroscopic behavior, paving the way to modulating the mechanical properties of elastomeric materials by tuning the nature of the curing agents. [Display omitted] [ABSTRACT FROM AUTHOR]

For carbon black (CB) absorbers with high dielectric loss, improving the impedance mismatch characteristics is the key to achieving high absorption of electromagnetic waves. Herein, acrylic resin (ACR) is served as the matching layer for CB, and core-shell CB@ACR nanocomposites are prepared by a solvent-free mechanochemical approach. The ACR shell is an insulating polymer that can avoid mutual contact between CB particles to form conductive channels, resulting in the optimization of the impedance matching. Specifically, methyl methacrylate is firstly grafted on the surface of CB by ball milling to improve the compatibility between CB and ACR, and then ACR is wrapped on its surface using the same method. The measurement results show that the ACR is successfully coated on the surface of the CB, forming a core-shell structure with a 14.8–33.3 wt% encapsulation ratio. With a proper encapsulation ratio, the minimum reflection loss of the CB@ACR composites is enhanced by about 160%, the widest effective absorption bandwidth is widened by about 642%, and the corresponding thickness becomes thinner than pristine CB, achieving a "stronger, wider, thinner." In summary, this work provides an innovative and effective approach to modifying absorbers for excellent microwave absorption performance. [Display omitted] [ABSTRACT FROM AUTHOR]