No abstract

A multi-step reduction process was developed to produce reduced graphene oxide (rGO) paper for electromagnetic interference (EMI) shielding. First step reduction was achieved by hydroiodic acid to remove most of the oxygen-containing functional groups, and sodium borohydride was used in the second step reduction to reduce carbonyl group which is the most difficult functional group to remove. In the last step reduction, hydroiodic acid was used as reducing agent again to remove the remaining oxygen-containing functional groups. The results show that this method can greatly improve the conductivity and EMI shielding performance of rGO paper. The resulting rGO paper with a C/O ratio of 19.38 and a thickness of 9.1[Formula: see text][Formula: see text]m exhibited high conductivity of 1084[Formula: see text]S/cm and excellent average EMI shielding efficiency of 45.84[Formula: see text]dB in the X-band, better than that reduction by other chemical methods.

Monodisperse polystyrene (PS) nanoparticles with widely tunable sizes (30–930 nm) were prepared by soap-free emulsion polymerization with the assistance of crown ethers. The effects of crown ether species and concentrations, initiator species, and monomer contents on the sizes of PS nanoparticles were investigated in detail. The presence of 18-crown-6 and 15-crown-5 in the reaction system will facilitate the polymerization rate of styrene and produce larger PS nanoparticles in comparison with the control group (without crown ethers), whereas the system with 12-crown-4 retards the polymerization rate significantly and brings the smallest PS nanoparticles. As the interface of monomer/water is the main locus of initial reaction for the thermally initiated emulsion polymerization, the crown ether/alkali complexes accumulated around the styrene/water phase play both catalyst and molecular fence roles in the styrene soap-free emulsion polymerization. The former promotes and the latter inhibits the growth of PS nanoparticles. The relative contribution of these functions ultimately determines the final particle size. The results indicate that particle nucleation in styrene soap-free emulsion polymerization in the presence/absence of crown ethers occurs via an aggregative nucleation mechanism. This study provides a facile method to synthesize nanoparticles with widely tunable sizes via soap-free emulsion polymerization with the help of crown ethers, which has great potentials in biomedical and electronic fields.

No abstract

No abstract