Doctor of Philosophy
School of Mechanical, Materials and Mechatronic Engineering - Faculty of Engineerinr
Mottaghitalab, Vahid, Development and characterisation of polyaniline - carbon nanotube conducting composite fibres, PhD thesis, School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2006. http://ro.uow.edu.au/theses/491
The present study describes methods for development and characterization of conducting electroactive polymer (CEP) fibre consisting of polyaniline (PAni) and single walled carbon nanotubes (SWNTs) which have potential applications as electronic devices to form building blocks of electronic textiles. The conducting composite fibres of PAni- SWNT were developed respectively using two steps (acid doping after fibre spinning) and one step methods (doping during preparation of spinning solution). The effectiveness of nanotube inclusion for improvement of mechanical, electrical and electrochemical properties was studied in each method. During development of the fibres, techniques such as UV-Vis-NIR, Raman spectroscopy, Dynamic light scattering and viscometery were used to characterise the quality of dispersion and spinning solutions. It has been shown that the N,N'-dimethyl propylene urea (DMPU) and dichloro acetic acid (DCAA) as solvents respectively for PAni in base and salt form are able to effectively disperse the pristine SWNTs to reach percolation level. The addition of nanotubes changes the rheological behavior of neat PAni spinning solution from a Newtonian to non-Newtonian shear thinning fluid based on power law regime which reflects nanotube-nanotube and/or nanotube-polymer physical entanglement. Several techniques including DMA, DSC, SEM, TEM, FIB, Raman spectroscopy, CV and four point probe electrical conductivity measurement were employed to characterize the various properties of the solid fibre. In both, one step or two steps methods, fibres containing SWNTs have superior tensile strength and elastic modulus compared with neat PAni fibre. The inclusion of SWNTs to PAni, however, decreases the elongation at break. These outcomes directly can be attributed to physical and/or chemical interfacial interaction between well distributed SWNTs bundles and the PAni matrix. The addition of nanotubes to the PAni matrix also increases the electrical conductivity and enhances the electrochemical redox process. However, the two step method was found to have some problem include low spinning rate, low flexibility and low conductivity and insufficient charge transfer along the fibre to be working electrode. These disadvantages were diminished by faster spinning of PAni- ES/2-acrylamido-2 methyl -1-propane sulfonic acid (AMPSA)/SWNT using the one step process with more than 5 times stretching ratio. An electronic conductivity percolation threshold of ~ 0.35 % w/w SWNTs was determined with fibres possessing electronic conductivity up to ~ 750 Scm-1. The well defined electrochemical window for neat PAni- ES/AMPSA fibre and its composite containing SWNT either in aqueous or ionic liquid electrolyte, with wider electrochemical window, confirms the ease of charge transport through a new conduction path for the fibre formed from salt structure, which was enhanced by addition of nanotubes. The ultimate tensile strength, elastic modulus and elongation at break of PAni-ES/AMPSA/SWNT fibres containing 0.76 % w/w nanotubes respectively were obtained 255 ± 32 Mpa, 7.3 ± 0.4 GPa and 4 ± 1 % compared with 170 ± 22 MPa, 3.4 ± 0.4 GPa and 9 ± 3 % for PAni-ES/AMPSA fibre. The quantitative analysis of nanotube orientation and detection of load transfer from matrix to nanotubes were investigated in PAni- S/AMPSA/SWNT composite fibre using Raman spectroscopy. It has been found that thermal stretching of as spun fibre mostly orients the nanotubes in a range of about ± 30° versus fibre axis which extremely increase the Herman orientation factor from 0.02 for as spun fibre to 0.43 for the 5x drawn fibre. Moderate orientation and Raman shift about 90- 130 cm-1 in D* band of SWNT be correlated to effective but not prefect load transfer between PAni matrix and nanotubes. The result of temperature dependent electrical conductivity data was shown that the higher conductivity of PAni-ES/AMPSA/SWNT composite fibre compared to neat PAni-ES/AMPSA fibre also can be described by improvement of the metallic property in the crystalline areas and boosting of the metallic disorder contribution in amorphous area. The consequence of improvement of mechanical, electrical and electrochemical properties were a benefit for applying of PAni/ES-AMPSA fibre and its composite having SWNT in applications as actuator, power source and sensor. While the fibres showed great promise as actuators, their response as batteries and temperature/ humidity sensors was limited. The significant improvement was observed in actuator strength in excess of 100 MPa and work-per-cycle of over 300 kJ/m3 through the incorporation of small amounts of SWNTs as reinforcement in the PAni matrix. This performance is 3 times higher than previously produced conducting polymer actuators and exceeds skeletal muscle in terms of stress generation by 300 times. PAni- ES/AMPSA/SWNT exhibited a higher charge/discharge capacity (12.4/11.2 mAhg-1) compared with the neat PAni-ES/AMPSA (4.5/4.1 mAhg-1). All the results show that solid polyaniline fibre can be used directly as electrode in ionic liquid of EMI.TFSI for wearable power source system. However its current performance is still well below conventional rechargeable battery systems. PAni fibre and its SWNT composite showed a nonlinear response with some delay to temperature signals. The PAni fibre incorporated with SWNTs showed lower sensitivity to change in humidity pulse compared with neat PAni fibre. This behavior has good opportunity for application in conducting yarn that needs the lowest variability in conductivity for transferring of electrical signal but clearly is not favored for sensing of humidity.