Mechanically Driven Activation of Polyaniline into Its Conductive Form

Abstract

Mechanical treatment of polymers produces surface cations and anions which, as demonstrated here for the first time, can drive chemical reactions. In particular, it is shown that such a mechanical treatment transforms nonconductive polyaniline into its conductive form. These results provide a mechanical means of patterning conductive polymers and also coating small polymer objects with conductive polyaniline films preventing accumulation of static electricity.Recent research on polymer mechanochemistry [1] -which aims to break or modify chemical bonds in polymers by mechanical stimuli-has demonstrated a range of mechanically driven reactions using both synthetic [2] and biological polymers [3] and sometimes displaying new reaction pathways. [4] In one exciting example, mechanochemical treatment of polymers incorporating trans and cis isomers of a 1,2disubstituted benzocyclobutene unit enabled electrocyclic ring opening, which, according to the Woodward-Hoffmann orbital symmetry rules, [5,6] should not be possible. In another work, 1,3-dipolar cycloreversions (reverse "click" chemistry), which are not possible under moderate thermal treatment, were made possible by mechanical input. These and several other reactions were enabled by incorporating into the polymers the so-called mechanophores, [6,7] which are functional groups designed to undergo a desired transformation. [8] Moreover, we [9] and others [10] have recently shown that it is also possible to drive mechanochemical reactions without the presence of mechanophores, using common polymers. In these systems, mechanical deformation of a polymer causes homolytic bond scission creating radicals, which then react with the surrounding solvent to yield hydrogen peroxide in quantities sufficient to synthesize nanoparticles, bleach dyes, or even turn on fluorescence visible to a naked eye.Homolytic cleavage is, of course, not the only pathway by which polymer bonds can break upon mechanical treatment. The bonds can also break heterolytically, forming surfacebound cations and anions, which form (+ /À) "mosaics" (Scheme 1) of surface charges of both polarities. [11a] In a recent series of publications, we [11] and others [12] have shown how these processes relate to the accumulation of static electricity which is a technologically useful process (e.g., in xerography) but also a source of shocks, explosions, and damage to electronic equipment. However, despite early reports [13] -which, were later refuted [11d, 14] -it has so far proven impossible to use these mechanochemically created surface charges in chemical applications, largely because the charges are rapidly annihilated in aqueous solutions. [15] Here we show, for the first time, that in non-aqueous but protic environments, these mechanoions can drive chemical reactions at material interfaces. In particular, we demonstrate that they can transform the non-conductive form of polyaniline (PANI) into its conductive salt. With spatially localized activation, our mechanical treatment allows for imprinting con...

Electrical Switchability and Dry-Wash Durability of Conductive Textiles

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