Synthesis of vertically aligned CNT-composite for membrane applications using chemical vapor deposition

Abstract

The work demonstrates fabrication of vertically aligned carbon nanotubes (CNT) composite using thermal chemical vapor deposition (CVD). A forest of vertically aligned CNTs was grown using catalytic CVD. Fluorocarbon polymer films were deposited in the spaces between vertically aligned MWCNTs using thermal CVD apparatus developed in-house. The excessive polymer top layer was etched by exposing the sample to water plasma. Uniform distribution of monomodel vertically aligned CNTs embedded in the deposited polymer matrix was observed in the micrograph, otherwise not possible using conventional techniques such as spin coating. The work also includes a simple technique for large scale horizontal and vertical alignment of single wall carbon nanotubes (SWCNTs). These horizontal patterns are key arrangements sought for fabrication of nanostructured materials. SWCNTs are purified and oxidized by treating them with nitric acid at 120-122oC. The oxidized SWCNTs are further reacted with octadecyl amine at the same temperature to attach the hydrophilic groups. These modified SWCNTs are dissolved and sonicated in tetrahydrofuran solution. The resulting uniform black color solution is filtered through 0.2 micro porous polytetraflouroethylene (PTFE) using Buckner filter. Horizontal and vertical alignment was achieved when filtration was performed under different conditions described in thesis. The contemporary alignment techniques are tedious and need special facilities. The current method is relatively simple and advantageously large quantities of CNTs can be aligned. Infrared spectroscopy confirmed the attachment of functional groups to CNTs. Alignment of CNTs, deposition of polymer and post etched specimens were analyzed by field emission scanning electron microscope (FE-SEM). Preliminary diffusion experiments are revealing and confirm the efficient deposition of polymer between the intertube gaps, as inferred from the permeable pore density and associated diffusion parameters.