| Two new sensor materials are reported: (1) a polymer electrolyte based on a tetrabutylammonium triiodide in poly(methyl methacrylate) (TBAI 3/PMMA) and (2) PANI-DNNSA; a soluble, electrically conductive polymer polyaniline, charge-balanced with dinonylnapthalenesulfonate, a bulky counterion with long alkyl tails.; Materials containing triiodide and other polyiodides have been previously studied and in certain cases it has been shown that they show large, reversible increases in conductivity in the presence of organic vapors (vapoconductivity). Thin films of TBAI3/PMMA also showed such vapoconductive effects with various vapors. The largest increase (104) was with methylene chloride vapor. The conductivity mechanism was studied using direct current conductivity measurements, A.C. impedence analysis, quartz crystal microbalance studies, dynamic mechanical analysis measurements, optical spectroscopy including IR, UV-vis, Raman spectroscopy, differential scanning calorimetry, and x-ray diffraction. It was concluded that the conductivity was ionic and that the vapoconductivity increase resulted from vapor-induced plasticization and solvation of TBAI3 resulting in free, mobile ions.; It was discovered that polar organic vapors increased the conductivity of PANI-DNNSA by up to five orders of magnitude. This change could be reversed using non-polar vapors.{09}The mechanism of this large conductivity change was determined using conductivity, UV, NIR, SEM, and XRD measurements. It was demonstrated that polar solvents cause poly(aniline) chains to become less coiled, which in turn leads to higher crystallinity. Conductivity increased because the conjugation length is extended, increasing electron transfer along the chains, and also because the chains are spaced closer together, improving electron transfer between chains.; The sensor properties of PMMA/TBAI3 and PANI-DNNSA material were investigated. Each material has been shown to differentiate between several organic vapors.{09}Since the vapoconductivity in each of these materials involves a different mechanism and different responses to the same vapors, the materials are good candidates for sensor elements in an array device (an electronic nose). |
