Preparation And Functional Behaviors Of Polyaniline@Carbon Nanotubes Composites

Conductive Polyaniline (PANi) hybridizing Carbon Nanotubes (CNTs), aliased as PANi@CNTs, were prepared by in situ polymerization of aniline on multi-walled carbon nanotubes (MWCNTs) or helical carbon nanotubes (HCNTs). The effects of composition and doping acid to PANi on the morphology and structure of the products were investigated. We studied the electromagnetic behaviors and electromagnetic wave refection loss of the PANi@CNTs composites. In addition, we investigated the NH3 gas sensitivity of the PANi@CNTs composites. The main results and achievements are as follows.We used HCl acid as the dopant, and ammonium persulfate as the oxidant for preparing one-dimensional PANi@CNTs composites by in situ polymerization. The results showed that the composites were nano dimention structures which PANi nanorods served as the shell and the CNTs as the core. It was proved by characterizations that there were interactions between PANi and CNTs in the composites. The PANi@CNTs composites with different diameters and wall thicknesses could be obtained by changing the reaction conditions, and the diameter of the composites decreased with CNTs mass percentage increasing. The doping effect of chiral camphor sulfonic acid to PANi result in higher degree of oxidation of the PANi in PANi@CNTs composites, while the HCl doped samples displayed more homogeneous in surficial morphology.Electrical conductivities of PANi@CNTs composites were tested by a four-probe measurement. The results demonstrated that the conductivity of PANi@MWCNTs increased with increase of MWCNTs contents, and decreased by chiral dopant used. The electrical conductivity of PANi@HCNTs increased with increase of HCNTs when HCNTs loading was less than 5 wt%, and decreased while HCNTs was higher than 10 wt%, and the chiral acid doping made the electrical conductivity increased. Comparatively tests and analyses indicated that PANi@CNTs composites displayed good performance of microwave absorption. When the mass percentage of MWCNTs was 10 wt%, the PANi@MWCNTs composites showed the best microwave absorption, the optimal absorption peak reached-23 dB at 4.7 GHz. The loss might be resulted from the eddy current loss in low-frequency region. Chiral doping effect led a shift from low frequency to high frequency of the reflection loss. When HCNTs content was 20 wt%, the composites displayed the best microwave absorption, and the lowest reflection loss was -31 dB located at 17.2 GHz. The excellent losses in wider frequency might be ascribed to the relaxation originated from interfacial polarization, and a new cross polarizing effect generated from helical structure of HCNTs. Chiral doping effect led a shift from low frequency to middle and/or high frequency of the reflection loss.A gas sensor testing system as set up to examine the sensitivity and response of PANi@HCNTs composites thin film to NH3 with concentration from 10 to 100. The results demonstrated that both the resistance and the response of the composites could be different and adjusted by controlling the contents of MWCNTs or HCNTs in the composites. Chiral doping may greatly enhance the response of PANi@MWCNTs to NH3 sensitivity, but reduce the response of PANi@HCNTs’.Based on experiential details, we recognized a microscopic mechanism of enhanced NH3 response by regulating the surficial morphology and hybridizing structure of PANi@CNTs.