Xiping Zeng

Structural dependence of silver nanowires on polyvinyl pyrrolidone (PVP) chain length

The effect of the chain length of polyvinyl pyrrolidone (PVP) on the structures of silver nanowires (AgNWs) is explored in this study. It was found in the experiments that PVP, when serving as a capping agent, has a great impact on the morphology and structure of AgNWs. By means of a series of experiments and the inquiry of the growth mechanism, the critical minimum PVP chain length for the successful formation of uniform nanowires was discovered, below which only nanoparticles or short nanorods can be obtained. Surprisingly, a core-shell structure of a nanowire with a polycrystal was observed when PVP with a very long chain length was employed in the processing.

Enhanced photochromic efficiency of transparent and flexible nanocomposite films based on PEO–PPO–PEO and tungstate hybridization

Nanocomposite hybrid films were prepared by depositing tungstate on PEO–PPO–PEO (EPE) templates under acidic conditions by a one-pot self-assembly sol–gel method. Uniform and transparent films based on this precursor were fabricated and easily manipulated using a facile casting method. Upon irradiation by sunlight, the film exhibits a rapid photochromic response that was reversible at room temperature. UV-Vis analysis revealed that folding of the –CH2–O– chains in the polymer and the larger tungstate clusters increased the red shift for the adsorption of visible light. The mechanism underlying the effect of hybridization of polyethylene oxide (PEO) on the enhanced photochromic effect was characterized by NMR, Raman and FTIR. The degree of folding of the –CH2–O– polymer chains was influenced by the presence of acid, which increased the oxygen coordination of WO6 and WO4 in the tungstate clusters. The characterized W–O bonding peaks shifted upon EPE incorporation, consistent with changes in oxygen coordination within the material. This weak coordination between tungstate and –CH2–O– improved the intervalence charge transfer (IVCT). Oxygen from EPE may enter the oxygen sites in the O–W–O clusters to produce an unbalanced electron state, resulting in oxygen defects, which has a critical effect on the enhancement of the photochromic response. In addition, this method provides protons via this weak coordination, thereby dramatically enhancing the efficiency of the hybrid film.

Wavelength Modulated SERS Hot Spot Distribution in 1D Nanostructures on Metal Film

Surface plasmons confining strong electromagnetic fields near metal surfaces, well-known as hot spots, provide an extremely efficient platform for surface-enhanced Raman scattering (SERS). In this work, SERS spectra of probing molecules in a silver particle–wire 1D nanostructure on a thin gold film are investigated. The Raman features of SERS spectra collected at the particle–wire joints exhibit an obvious wavelength dependence phenomenon. This result is confirmed electromagnetic field simulation, revealing that hot spot distribution is sensitively influenced by the wavelength of incident light at the joints. Further studies indicate this wavelength dependence of hot spot distribution is immune to influence from the geometric shape of the particle or the angle between wire and particle, which improves fabrication tolerance. This technology may have promising applications in surface plasmon related fields, such as ultrasensors, solar energy and selective surface catalysis.

Surface evolution of manganese chloride aqueous droplets resulting in self-suppressed evaporation.

The exchange kinetics of liquid water, which are of fundamental interest and have potential applications, remain unclear. A fantastic and extraordinary phenomenon was observed during the evaporation of a water droplet doped with manganese chloride. As observed from the evolution of this type of droplet, a thin film was formed on the surface with an exothermic phase transition, resulting in self-suppressed evaporation. The MnCl2-doped water droplets were maintained in a relative humidity (RH) of 50% at 40 °C for more than a week and for longer than two months at a temperature of 25 °C. In contrast, a pure water droplet can only be sustained for a few minutes. The self-suppressed evaporation of doped water may be due to the special hydration of the accumulated manganese and chloride ions at the surface, decreasing the surface tension.