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Open Access Nano Express

Temperature-dependent gas transport performance of vertically aligned carbon nanotube/parylene composite membranes

Lei Zhang1, Junhe Yang1*, Xianying Wang1, Bin Zhao1* and Guangping Zheng2

Author Affiliations

1 School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China

2 Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

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Nanoscale Research Letters 2014, 9:448  doi:10.1186/1556-276X-9-448

Published: 28 August 2014

Abstract

A novel composite membrane consisting of vertically aligned carbon nanotubes (CNTs) and parylene was successfully fabricated. Seamless filling of the spaces in CNT forests with parylene was achieved by a low-pressure chemical vapor deposition (CVD) technique and followed with the Ar/O2 plasma etching to expose CNT tips. Transport properties of various gases through the CNT/parylene membranes were explored. And gas permeances were independent on feed pressure in accordance with the Knudsen model, but the permeance values were over 60 times higher than that predicted by the Knudsen diffusion kinetics, which was attributed to specular momentum reflection inside smooth CNT pores. Gas permeances and enhancement factors over the Knudsen model firstly increased and then decreased with rising temperature, which confirmed the existence of non-Knudsen transport. And surface adsorption diffusion could affect the gas permeance at relatively low temperature. The gas permeance of the CNT/parylene composite membrane could be improved by optimizing operating temperature.

Keywords:
Carbon nanotube; Composite membrane; Gas transport; Parylene