X.Q. Yang

Highly ordered thin films of polyheterocycles: A synchrotron radiation study of polypyrrole and polythiophene Langmuir-Blodgett films

Abstract Langmuir-Blodgett films have been made with 3-n-hexadecylpyrrole and 3-n-octadecylpyrrole monomers and copolymers with unsubstituted pyrrole made by chemical polymerization at the air-water interface on a subphase containing FeCl 3 . Langmuir-Blodgett films consisting of mixtures of stearic acid and alkylsubstituted polythiophenes have also been made as bilayer films. The orientation of single and multilayer films on platinum substrates have been studied by Near Edge X-ray Absorption Fine Structure Spectroscopy which also gives information about charge transfer interactions between the aromatic groups and the metallic substrates. The alkylsubstituted pyrroles form highly ordered two-dimensional structures. FeCl 3 initiated copolymerization with unsubstituted pyrrole leads to a more disordered system. In the case of polythiophene-stearic acid bilayers, the stearic acid layers are highly ordered. The poly(alkyl thiophene) layers sandwiched between stearic acid layers, on the other hand, exhibit random orientation of the thiophene moieties.

Ordered Langmuir-Blodgett films of polypyrrole and analogs

Abstract Ordered mono and multilayers of polypyrrole and its analogs were prepared using a Langmuir-Blodgett film balance. Films could be transferred with facility and were picked up on microscope grids for electron microscopic studies among a number of other investigations. Scanning electron microscopy (SEM) revealed a smooth coverage over a large surface area of the substrate. Electron diffraction from these thin films revealed that the nature of packing is substantially different from bulk grown polypyrrole.

Electrochemical Polymerization of Pyrrole Derivatives

Abstract Electrochemical copolymerization of pyrrole and 3-(6-ferrocenyl-6-hydroxyhexyl)pyrrole (P-Fc) yields a ferrocene functionalized polypyrrole with a controlled amount of ferrocene functionalization. Similarly, copolymers of pyrrole and 3-(4-(2,5-dimethoxyphenyl)butyl)pyrrole (P-MP) can be made by electrochemical polymerization and converted to the copolymers containing pH dependent electroactive hydroquinone moieties.

A FTIR and NEXAFS study of polypyrrole Langmuir-Blodgett films

Abstract 3-n-hexadecylpyrrole and 3-n-octadecylpyrrole have been synthesized, and Langmuir Blodgett films of these compounds have been studied by means of NEXAFS and FTIR spectroscopy. By comparing the spectra of two different polarizations, it was found that the hydrocarbon chains are normal to the substrate surface for LB films with multi-layers. For the monolayer LB films, the hydrocarbon tails are tilted towards the substrate surface due to the interaction between the pyrrole ring and the platinum substrate.

X‐ray absorption study of diamond films grown by chemical vapor deposition

Carbon k‐edge x‐ray absorption fine structure (XAFS) is used to study the structure and bonding of chemical vapor deposition (CVD) grown diamond and diamond‐like carbon films. Diamond films grown at 875 °C on silicon using a 1% CH4 /H2 mixture have near‐edge spectra resembling type 1(a) natural diamond. The k‐edges of the diamond‐like films grown by electron cyclotron resonance CVD at 200 °C using 10−4 Torr of CH4 show a broad main peak lacking the sharp structure of graphite or diamond. Comparing the near edges of the CVD diamond film with other carbon compounds (i.e., graphite) and the CVD diamond film, the diamond‐like film shows a strong π* feature at 285 eV indicative of sp2 bonded carbon and a feature at 289 eV, the σ*(C–H) resonance indicating C–H bonds. The relatively weak extended x‐ray absorption fine structure (EXAFS) shows that the diamond‐like carbon film is highly disordered on an atomic level.

Orientational behavior of thin films of poly(3-methylthiophene) on platinum: A FTIR and NEXAFS study

Abstract Near edge x-ray absorption fine structure (NEXAFS) and infrared reflection-absorption spectroscopy (IRRAS) have been used to study the orientational behavior of thin films of poly(3-methylthiophene) electrochemically polymerized on a platinum surface. Clear orientational effects, with the thiophene rings predominantly oriented parallel to the platinum surface, were observed when the thickness of the polymer films were within a few hundred A. It was found that more highly ordered films were produced at lower polymerization potential (1.4V vs SCE) than at higher potential (1.8V vs SCE).

Structure and Phase Transitions in PEO-KI Complexes

Abstract In the 1970s Wrightl1-2 and later Armand et aL3 suggested that poly(ethy1ene oxide) (PEO) complexed with alkali metal salts could be used as thin film polymeric solid electrolytes. Since this original work we have witnessed a rapid expansion of research and development of this class of conducting polymers.

Temperature dependent structure of conducting Langmuir Blodgett films studied by X-ray scattering

Electrically conductive Langmuir-Blodgett films were fabricated from mixtures of stearic acid and poly(3-hexylthiophene). The temperature dependent structure of these films as well as that of pure stearic acid LB films was studied using x-ray scattering. We were able to use a crystal analyzer in front of the detector to greatly improve the angular resolution by taking advantage of the high intensity of the x-ray beam from the synchrotron storage ring. A phase separation indicated by a d-spacing change along the stacking direction was observed upon varying the temperature. The in-plane two dimensional structure of these LB films was studied and the temperature dependence indicates a phase transition of the in-plane structure in the temperature range of 90°C to 110°C for the pure stearic acid LB film

Orientational Effects in 3-n-Hexadecylpyrrole Langmuir-Blodgett films

Abstract 3-n-hexadecylpyrrole have been synthesized, and Langmuir-Blodgett films of this compound have been studied by means of transmission and grazing incident reflection FT-IR spectroscopy. A comparison of the spectra at the two different polarizations shows that the hydrocarbon tails are oriented normal to the substrate surface for multilayer LB films. For the single monolayer LB films, the hydrocarbon tails are tilted with respect to the substrate surface possibly due to interactions between the pyrrole head groups and the platinum substrate.

Molecular Organization and Electrical Properties of Mixed Langmuir-Blodgett Multilayer Thin Films of Polypyrrole

The molecular organization of Langmuir-Blodgett multilayer thin films containing electrically conductive polypyrrole chains dispersed throughout insulating domains of surface active pyrrole molecules was examined by several thin film spectroscopic techniques. Reflection-absorption FTIR and NEXAFS spectroscopy have revealed that the 3-ODOP (3-octadecanoyl pyrrole) surface active pyrrole molecules are highly oriented within the film with their fully extended hydrocarbon chains tilted away from the surface normal with an unusually large tilt angle of about 55°. Evidence for preferred orientation of the polypyrrole chains was also found. The multilayer films were found to exhibit very large dielectric constants (>100) at low frequencies and enormous conductivity anisotropics. These unusual electrical properties can be directly attributed to the molecular organization of the film which consists of polypyrrole chains sandwiched between well ordered layers of 3-ODOP molecules.