%0 Conference Paper %B Materials Research Society Spring Meeting %D 2005 %T A structural investigation of polypyrrole as a function of oxidation state %A Warren, M R %A Madden, J D %C San Francisco %I Materials Research Society %P I6.1 pp. 1-6 %U http://www.mrs.org %V 871E %X Polypyrrole exhibits actuation under electrochemical doping and undoping of the polymer matrix. Active strain and x-ray diffraction measurements are performed in order to correlate the microscopic and macroscopic structural changes occurring during actuation. Under galvanostatic reduction, the film shows first a linear contraction with oxidation state due to expulsion of small anions. At 50% of the as-grown doping level, the film reverses direction and begins to expand due to incorporation of the larger cations. X-ray diffraction, however, does not show a linear contraction in the crystalline portions of the polymer. The polymer crystallites go through a sudden contraction in one dimension of approximately 14%, and otherwise remain constant. The contraction in the polypyrrole crystals occurs at the 50% doping level, and appears to be correlated with the reversal of macroscopic actuation.