Perfluoroalkylsilane-Modified Boron Nitride Nanosheets for Epoxy Composites with Improved Thermal Conductivity and Dielectric Performance

The development of polymer-based packaging materials with excellent heat dissipation capacities and low dielectric constants is increasingly desired for the modern microelectronic industry. Herein, boron nitride nanosheets (BNNSs) were coated with polydopamine (PDA) and subsequently grafted with tridecafluorooctyl trimethoxy silane. Compared with unmodified BNNSs, as-prepared perfluoroalkylsilane-modified BNNSs (PFOS-BNNSs) show distinctly improved miscibility in the epoxy matrix. Consequently, the epoxy/PFOS-BNNSs (30 wt %) composite shows a higher thermal conductivity of 1.15 W m–1 K–1, which increases by 538 and 42% when compared to the neat epoxy and the epoxy/BNNSs composite, respectively. Notably, the ultralow molar polarizability of C–F bonds enables the epoxy/PFOS-BNNSs composite to have lower dielectric constant and dielectric loss tangent than those of the epoxy/BNNSs composite. Finally, the impacts of the surface modification of BNNSs on the rheological, thermal, and mechanical properties of the resulting epoxy composites were also investigated in detail

Key Role of Bismuth in the Magnetoelastic Transitions of Ba₃BiIr₂O₉ and Ba₃BiRu₂O₉ As Revealed by Chemical Doping

The key role played by bismuth in an average intermediate oxidation state in the magnetoelastic spin-gap compounds Ba₃BiRu₂O₉ and Ba₃BiIr₂O₉ has been confirmed by systematically replacing bismuth with La³⁺ and Ce⁴⁺. Through a combination of powder diffraction (neutron and synchrotron), X-ray absorption spectroscopy, and magnetic properties measurements, we show that Ru/Ir cations in Ba₃BiRu₂O₉ and Ba₃BiIr₂O₉ have oxidation states between +4 and +4.5, suggesting that Bi cations exist in an unusual average oxidation state intermediate between the conventional +3 and +5 states (which is confirmed by the Bi L₃-edge spectrum of Ba₃BiRu₂O₉). Precise measurements of lattice parameters from synchrotron diffraction are consistent with the presence of intermediate oxidation state bismuth cations throughout the doping ranges. We find that relatively small amounts of doping (∼10 at%) on the bismuth site suppress and then completely eliminate the sharp structural and magnetic transitions observed in pure Ba₃BiRu₂O₉ and Ba₃BiIr₂O₉, strongly suggesting that the unstable electronic state of bismuth plays a critical role in the behavior of these materials