Dry densification of carbon nanotube bundles

A dry method for densifying vertically aligned carbon nanotube bundles is proposed and experimentally validated. The process uses the deposition of thin SiO2 films to seal the porous CNT bundles at low pressure. When the CNT bundles are transferred back to ambient pressure they are densified by the pressure difference obtained between the inner and outer sides of the thin film. The effects of the densification have been studied for different thicknesses of SiO2 films deposited by two different deposition techniques. The diameters of the narrowest densified sections are 26 ± 3% of their original sizes after dry densification by 50 nm thick SiO2. The proposed dry densification method is also compared to existing liquid-based methods and its limitations are discussed.