A universal but simple procedure for identifying the α, β and γ phases in PVDF using FTIR is proposed and validated. An integrated quantification methodology for individual β and γ phase in mixed systems is also proposed.

A near-field electrospinning (NFES) process has been developed to deposit solid nanofibers in a direct, continuous, and controllable manner. A tungsten electrode with tip diameter of 25 µm is used to construct nanofibers of 50−500 nm line width on silicon-based collectors while the liquid polymer solution is supplied in a manner analogous to that of a dip pen. The minimum applied bias voltage is 600 V, and minimum electrode-to-collector distance is 500 µm to achieve position controllable deposition. Charged nanofibers can be orderly collected, making NFES a potential tool in direct write nanofabrication for a variety of materials.Electrically driven liquid jets and the stability of electrically charged droplets have been studied for hundreds of years, 1,2 while the practical apparatus of electrospinning, in which a charged jet of polymer solution is deposited onto a collector under the influence of an electrical field, dated back in 1934. 3 The feasibility to construct long and continuous polymeric, 4-6 ceramic, 7 and composite 8 nanofibers as well as nanotubes 9 with diameters less than 100 nm has been demonstrated using electrospinning. Typical applications include bioscaffolding, 10 wound dressing, 11 and filtrations 12 to name a few. Researchers have further explored the possibilities of using electrospun nanofibers in fabricating micro-and nanodevices such as field effect transistors, 13 gas 14 and optical sensors, 15 and deposition of DNA on functional chips. 16 In these and other applications, the controllability of the electrospinning process is critical. Unfortunately, current setup of electrospinning is unstable in nature as it relies on the chaotic whipping of liquid jets to generate nanofibers. Limited works toward the control of electrospinning have emerged, including aligning nanofibers by electrical field 17 and using rotational mechanical mandrels. 18,19 Furthermore, numerous investigations by means of analytical and experimental methodologies have been conducted to study the fundamental physics and chemistry of electrospinning for further improvement and control, such as the effects of polymer solution concentration, applied voltage, and electrode-to-collector distance. 4,[20][21][22] Here we report experiments of controllable electrospinning based on a new type of "near-field" electrospinning (NFES). Figure 1A illustrates the schematic setup of NFES that merges several disparate concepts. First, the electrode-to-collector distance, h, is in the range of 500 µm to 3 mm to utilize the stable liquid jets region for controllable deposition. Second, a solid tungsten spinneret of 25 µm tip diameter as illustrated in Figure 1B is used in NFES to achieve nanofibers with sub-100-nm resolution. Third, the applied electrostatic voltage is reduced due to the short electrode-to-collector distance while the electrical field in the tip region maintains the strength in the range of 10 7 V/m as those used in conventional electrospinning to activate the process. Fourth, discrete droplets of polymer solu...

The first synthesis of MnO@Mn O nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn O /NPCF) through pyrolysis of mixed-valent Mn clusters is reported. The unique features of MnO@Mn O /NPCF are derived from the distinct interfacial structure of the Mn clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn O are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn O , the uniform distribution, and the NPCF, MnO@Mn O /NPCF displays unprecedented lithium-storage performance (1500 mA h g at 0.2 A g over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn O and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

We report a rational design of separator for lithium-ion batteries by the polydopamine–ceramic composite-modification of polyolefin membranes, which leads to substantially enhanced thermal and mechanical stability.