Spectroscopic Studies of the Structure and Orientational Effects of Electroresponsive Polymeric and Langmuir-Blodgett Films

The microscopic structure, bond length, orientation, and coordination number of a series of electroresponsive molecular and polymeric systems were studied by several spectroscopic techniques: Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, X-ray diffraction, and Fourier-Transform Infra-Red (FTIR) spectroscopy. The studies concern ion complexation in poly(ethylene oxide), and the structure and orientation of pyrrole and thiophene based Langmuir-Blodgett (LB) films and electrochemically polymerized poly(3-methylthiophene) films. The temperature dependence of the coordination number of oxygen around the cation K^{+} in the ion-conducting polymer complex of poly(ethylene oxide) and potassium iodide was studied with EXAFS and NEXAFS spectroscopies. NEXAFS spectroscopy also is a sensitive probe of the orientational behavior of LB films. The relative intensities of the absorption peaks from the core level ground state to sigma* and pi* antibonding states at different incident angles of the x-ray beam can be used to calculate the orientation of the molecules. In the near-edge C K-edge spectra of various LB films, a charge transfer interaction between a polymer film and its metallic substrate was also observed. The layer structure and in-plane structure of LB films were studied by x-ray diffraction. A clear superlattice structure was observed in Y-type LB films. The temperature dependance of the structure of LB film also was studied by x-ray diffraction. The orientation and ordering of thin films of the electron conducting polymer poly(3-methylthiophene) were also studied by NEXAFS, and FTIR spectroscopic techniques. The results of the NEXAFS and the FTIR experiments are consistent.