Editing Polypyrrole (section)

==Properties==
Films of PPy are yellow but darken in the air due to some oxidation. Doped films are blue or black depending on the degree of polymerization and film thickness. They are amorphous, showing only weak diffraction. PPy is described as "quasi-unidimensional" vs one-dimensional since there is some crosslinking and chain hopping. Undoped and doped films are insoluble in solvents but swellable. Doping makes the materials brittle. They are stable in the air up to 150&nbsp;°C at which temperature the dopant starts to evolve (e.g., as HCl).<ref name=RussChemRev/>

Doping the polymer requires that the material swell to accommodate the charge-compensating anions. The physical changes associated with this charging and discharging have been discussed as a form of artificial muscle.<ref>{{cite journal | last1 = Baughman | first1 = Ray H. | year = 2005 | title = Playing Nature's Game with Artificial Muscles | journal = Science | volume = 308 | issue = 5718| pages = 63–65 | doi = 10.1126/science.1099010 | pmid=15802593| s2cid = 180181717 }}</ref> The surface of polypyrrole films present [[fractal]] properties and ionic diffusion through them show [[anomalous diffusion]] pattern.<ref>Ahmad Sharifi-Viand, [http://www.sciencedirect.com/science/article/pii/S0042207X15000032 Diffusion through the self-affine surface of polypyrrole film] ''Vacuum'' doi:10.1016/j.vacuum.2014.12.030
</ref><ref>{{cite journal | last1 = Sharifi-Viand | first1 = Ahmad | year = 2012 | title = Investigation of anomalous diffusion and multifractal dimensions in polypyrrole film | journal = Journal of Electroanalytical Chemistry | volume = 671 | pages = 51–57 | doi=10.1016/j.jelechem.2012.02.014}}</ref>