Lixia Gu

Studies on the antistatic mechanism of tetrapod-shaped zinc oxide whisker☆

Abstract Antistatic composites of polyurethane, polyvinyl and natural rubber with the electrical resistivity of 106– 10 10 Ω cm were prepared using tetrapod-shaped zinc oxide whisker as the conducting additives. The conductive behavior of this system has been analyzed and the results show that the tetrapod-shaped ZnO whisker is an effective antistatic additive for polymer materials. A formula of critical volume fraction of ZnO whisker for the formation of the conducting paths of the polymer/ZnOw composite has been put forward and compared with the experimental results. The analysis of the conductive mechanism indicates that the charge concentrating effect at the needles’ tips of the whisker will be distinct if the material is under an electric field. The tunnel effect may exist and cause leakage current in this kind of composites.

Actual air separation across multilayer composite membranes

Multilayer composite membranes are fabricated from six types of thin films as selective layers, an ethyl cellulose (EC) thin film as a flexible spacer, and poly(ether sulfone) (PES) with 15–45 nm pore size or 100–120 μm thickness as a porous support layer. The effects of the thin-film type and its layer number, operating temperature, and transmembrane pressure difference, as well as the operational time on the actual air-separation properties through the composite membranes, are investigated by a constant pressure-variable volume method. The results show that a pure polystyrene thin-film composite membrane exhibits poor actual air-separation performance due to its brittleness, although it has a higher ideal oxygen over nitrogen separation factor. The oxygen-enrichment air (OEA) flux through all of the composite membranes tested increases significantly with increasing operating temperature and pressure difference. The oxygen concentration in the OEA increases slightly with an increase in operating temperature, and the oxygen concentration through the polystyrene/cholesteryl oleyl carbonate blend, top layer composite membrane exhibits the maximal value. As the transmembrane pressure difference increases, the oxygen concentration in the OEA also exhibits the maximal value. The maximum oxygen concentration can reach 39.1%, which is achieved by the multilayer composite membrane consisting of a polystyrene/cholesteryl oleyl carbonate (95/5) monolayer, an EC single flexible spacer, and a PES support at 35°C and a transmembrane pressure difference of 550 kPa.