Nanostructure of Electrically Conducting Polyaniline Prepared by a Novel Emulsion Polymerization Process
- PDF / 3,760,929 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 56 Downloads / 166 Views
This work deals mainly with the characterization of the nanostructure of PANI polymer films. Transmission electron microscopy techniques were employed to extract information about the structure and morphology of conducting PANI films and their structural modifications by surfactants or solvents. EXPERIMENT METHODS A detailed discussion of the synthesis of the PANI salt and the emulsion polymerization process is reported elsewhere in these proceedings [6]. Briefly, the emulsion process entails formation of emulsion particles with a mean hydrodynamic diameter of 210 nm and consists of a water-soluble organic solvent (e.g., 2-butoxyethanol), a water-insoluble organic acid (dinonylnaphthalene sulfonic acid (DNNSA)), aniline and water. Aniline is protonated by the organic acid to form a salt that partitions into the organic phase. As oxidant (ammonium peroxydisulfate) is added to the reaction mixture, PANI intermediates are formed in the organic phase. As the reaction proceeds, the emulsion flocculates to form a two-phase system with soluble PANI remaining in the organic phase. The concentrated PANI-DNNSA can be readily dissolved in xylene or other solvents [6]. A 5% solution of the PANI-DNNSA complex in pure xylene was produced. Electron beam transparent films were prepared by dip coating a gold grid at various speeds. These ultra thin films were then directly examined in a JEOL 2000FX TEM microscope equipped with a Gatan slow-scan CCD camera. It was found that the PANI-DNNSA films were sensitive to electron beam irradiation. At normal electron beam doses, the crystalline nature of the PANI-DNNSA was destroyed. The radiation damage necessitates the use of low-dose procedures to record the TEM images of PANI-DNNSA polymer films. All TEM images reported here were acquired digitally with the slow-scan CCD camera at low electron doses. After TEM images were recorded, the PANI films were taken out of the microscope for treatment with surfactants such as benzyltriethylammonium chloride (BTEAC) or with low molecular alcohols and ketones such as methanol and acetone. These treated films were then reexamined in the microscope to observe the structural and/or morphological modifications of the PANI films due to the chemical treatment. RESULTS AND DISCUSSIONS Nanostructure of PANI-DNNSA Films Figure 1 shows a typical bright field TEM image of the PANI-DNNSA films. A large number of small dark spots with diameters ranging from 10 to 30 nm were incorporated into a less dense matrix (white regions). The darker spots or domains represent conducting PANIThe DNNSA islands. The brighter regions represent non-conducting dopant phase. distribution of the PANI-DNNSA islands was not uniform within the polymer film. In some regions, these small islands aggregated to form domains with a high density of PANI-DNNSA islands. The conducting PANI-DNNSA regions were clearly not very well inter-connected in the polymer film. These small dark spots can be viewed as colloidal particles of PANIDNNSA complexes in the diluted xylene/PANI-DNNSA solution.
Data Loading...
