Jichun Liu

Triple percolation behavior and positive temperature coefficient effect of conductive polymer composites with especial interface morphology

Selective localization of carbon black (CB) at the interface of polymer blends was achieved by the method that poly(styrene-co-maleic anhydride) (SMA) was first reacted with CB, and then blended with nylon6/polystyrene (PA6/PS). In the PA6/PS blends, CB was localized in PA6 phase and typical double percolation was exhibited. In the PA6/PS/(SMA–CB) blends, TEM results showed that CB particles were induced by SMA to localize at the interface, resulting in the especial interface morphology fabricated by SMA and CB. The especial interface morphology of PA6/PS/(SMA–CB) caused distinct triple percolation behavior and very low percolation threshold. The positive temperature coefficient (PTC) intensity of PA6/PS/(SMA–CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient (NTC) effect was eliminated. The elimination of NTC effect was arisen from the especial interface morphology. A stronger PTC intensity was attributed to the low percolation threshold and the morphology.

The Adaptive Tribological Investigation of Polycaprolactam/Graphene Nanocomposites

The design and mechanism of adaptive materials in the field of tribology are of particular importance because of the tribological properties greatly depending on the operating conditions and external environment. Polycaprolactam (PCL) adaptive nanocomposites containing porous graphene impregnated with solid paraffin were prepared by in situ polymerization. The tribological results showed that the designed nanocomposites, which displayed adaptive tribological behaviors, had low and stable friction coefficients and the wear rates compared to neat PCL even under high pressure and velocity condition. The proposed adaptive tribological mechanisms are due to the high load-carrying capabilities of graphene nanosheets forming proper surface texture, the lubricating role of molten paraffin produced at sliding interface under friction heating and the mitigated thermal damage caused by lower surface temperature through depleting friction heat. The as-prepared polycaprolactam composites are expected to broaden the application of such polymers in engineering parts, and the design concept can easily apply to other self-adaptive tribological composites.

PVP-stabilized Ru colloidal nanoparticles by solvothermal synthesis: Preparation, characterization, and catalytic properties

ABSTRACT Stable poly (N-vinyl-2-pyrrolidone)-stabilized ruthenium colloidal nanoparticles (PVP-Ru) were prepared by solvothermal method; n-butyl alcohol, a low boiling point alcohol, was used as the reductant and solvent and PVP (polyvinyl pyrrolidone) served as protecting agents. PVP-Ru nanoparticles were characterized by UV-Vis absorbance spectra (UV-Vis), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FT-IR). The PVP-Ru colloidal nanoparticles were applied to catalytic oxidization of ethanol to evaluate the catalytic activity, and the products were analyzed by gas chromatograph (GC). The results showed that the average diameter of the Ru nanoparticles was 1.23 nm with a narrow distribution. X-ray photoelectron spectroscopy verified that Ru was in the metallic state. The PVP-Ru colloidal nanoparticles possessed high catalytic activity and selectivity for the oxidation of gas ethanol to acetaldehyde.

Double PTC Effect of Carbon Nanotubes Filled Immiscible Polymer Blends

Carbon nanotubes(CNTs) and poly(styrene- co- maleic anhydride) modified CNTs(SMACNTs) were blended with an immiscible system polystyrene/nylon6(PS/PA6) to prepare conductive polymer composites PS/PA6/CNTs and PS/PA6/SMA-CNTs respectively.The PTC(positive temperature coefficient) effect of the composites was investigated.For PS/PA6/CNTs composites,CNTs were selectively distributed in PA6 phase;the percolation threshold was 5%(mass fraction) and a weak PTC effect was observed.For PS/PA6/SMA-CNTs composites,TEM results showed that CNTs were distributed both at the PS/PA6 interface and in PA6 phase due to the induced effect of SMA on CNTs.As a consequence,the percolation threshold decreased to 0.112%.Meanwhile,an especial double PTC effect was observed.The PTC effect was affected by the morphology of PS/PA6 blends.The emerge of PTC effect of the composites with dispersed PA6 phase was attributed to the glass transition of PS phase and the melt of PA6 phase.However,for blends with PS as disperse phase and PS/PA6 as bicontinuous phases,the emerge of PTC effect was due to the melt of PA6 phase.