The Research Of Conductive Composite-Sulfonated Polyphenylacetylene/Multi-walled Carbon Nanotubes

Conductive composites were varied applied in many fields, such as electromagnetic interference (EMI) shielding, radio frequency interference (RFI) shielding, electrostatic dissipation of charge (ESD), conductive adhesives and circuit elements in microelectronics, etc.Sulfonated poly-phenylacetylene (SPPA), is a conjugated polymer with metal-color. Carbon nanotubes (CNTs) are characterized by exceptional mechanical, electrical and optical properties. Many studies using transmission electron microscopy (TEM) show that numerous structural defects are present in the multiwalled nanotubes (MWNTs), so that electron donors and acceptors can dope them.In our works, we prepared the SPPA/MWNTs composites by blending the SPPA with MWNTs. During the investigation of the electrical properties, we found special phenomena, so more research was conducted to repeat and explain these. On the basis of this research, we put forward the conductive mechanism. Here is the main content.1 Preparation and characterization for SPPA/MWNTs compositesThe PPA was obtained by situ polymerization, and was treated with Sulfuric acids to get SPPA. We got purified MWNT_S by refluxing Pristine MWNT_S with 4 mol.L^-1 HNO₃ for 4 h at 130°C. Finally, SPPA/MWNTs composites were obtained by mixing MWNTs and SPPA in tetrahydrofuran (THF) within an ultrasonic bath. In order to make sure the production, we observed them using a FT-IR, a transmission electron microscope, an element analysis instrument.2 Electrical conductivityUsing an element analysis instrument, a four-point probe, an insulation/ electric leakage current measurement and temperature control chamber etc., we investigated the dependencies of electrical conductivity on sulfur content, MWNTs contents and temperature. The results showed that the larger the sulfur content is, the higher the electrical conductivity is, and that the electrical conductivity increased with increasingtemperature, namely "Negative Temperature Coefficient (NTC) of resistance". The plots of electrical activity as a function of the MWNTS content for SPPA/MWNTS composites, had two obvious increases in conductivity and a low critical value.3 MWNTs doping SPPAXPS showed that the peaks moved towards the higher energy direction, and the UV-Vis-IR displayed that the peaks had some red shift. The results obtained using XRD showed that in the composites, the peak at 9.5( ) became sharper and stronger than that of pure SPPA. All of these indicated that SPPA has been doped by MWNTS, and that there was some charge transfer and interaction between SPPA and MWNTs in composites. In addition, we hold that because of the charge transfer between SPPA and MWNTs, some interaction existed between the two of them; therefore, the crystallization of SPPA improved. The FESEM revealed that MWNTs distribute discontinuously in the vicinity of the percolation threshold. 4 Conductive mechanismOn the basis of the above analysis, we came to the conclusion about the conductive mechanism. SPPA are both filled and doped by MWNTs, then the conductive networks in SPPA/MWNTs composites consists of two kinds of conductive system. One is formed via conductive units connecting, and the other is formed by MWNTS contact. Further, we built a theoretical model to explain the conductive mechanism.