K. Hong

Synthesis of electrically conductive polypyrroles at the air-water interface of a Langmuir-Blodgett film balance☆

Electrically conductive monolayers of polypyrroles have been synthesized at the air-water interface of a Langmuir-Blodgett film balance. This was accomplished by spreading a mixture of pyrrole monomer and a surface-active pyrrole derivative (3-octadecyl pyrrole) onto a subphase containing an oxidizing aqueous solution of FeCl3. The resultant electrically conductive films can be subsequently compressed into a condensed monolayer in which they exhibit the surface pressure- area characteristics of the 3-octadecyl pyrrole in a slightly expanded state. It has also been found that neither the pyrrole nor the 3-octadecyl pyrrole will react at the air- water interface to produce electrically conductive materials under the conditions used to polymerize the mixture. In other words, electrically conductive monolayers can only be produced from spreading solutions containing both the surface-active pyrrole and pyrrole monomer. Preliminary IR analysis indicates that the newly formed polymer monolayer comprises both pyrrole and alkyl pyrrole units.

Formation and properties of electrically conductive Langmuir-Blodgett multilayer thin films of the poly(3-alkyl thiophenes)

Abstract Langmuir-Blodgett multilayer thin films were fabricated from mixed monolayers containing stearic acid and various poly(3-alkyl thiophenes). It was found that stable monolayers and highly ordered multilayers could be formed with poly (3-alkyl thiophenes) fitted with alkyl chain lengths ranging from four carbons to eighteen carbons. X-ray diffraction revealed that the multilayers formed from these materials have well defined layer spacings. Chemical oxidation and ion implantation techniques were used to render the thin films electrically conductive. X-ray diffraction and optical measurements revealed that significant disorder results from the ion implantation process.

Fabrication of novel electrically conductive Langmuir-Blodgett thin films of the poly(3-alkylthiophenes)

Abstract Electrically conductive Langmuir-Blodgett (LB) multilayer thin films were fabricated from mixed monolayers containing steatic acid and poly(3-hexylthiophene). It has been found that stable monolayer films can be formed at the air-water interface from mixtures containing as much as 80 mol.% of poly(3-hexylthiophene). The monolayers were found to undergo a transition from a mixed monolayer to a bilayer structure at elevated surface pressures. The mixed monolayers were successfully transferred onto solid substrates as Y-type films by the vertical lifting method. These LB films exhibit well-defined layered structures as determined by optical, capacitance and X-ray diffraction measurements. The multilayer LB films were rendered electrically conductive by doping with strong oxidizing agents. In some cases, conductivities as high as 2 S cm −1 were obtained by this doping process.

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.

Langmuir-Blodgett thin films of electrically conductive surface-active polypyrroles

Abstract Electrically conductive polypyrroles have been synthesized at the air-water interface of a Langmuir-Blodgett film balance by spreading mixtures of pyrrole monomer and a surface-active pyrrole derivative (3-octadecyl pyrrole or 3-octadecanoyl pyrrole) onto a subphase containing ferric chloride. The thickness and conductivity of the resultant polymers were found to depend strongly on the mole ratio of surface-active pyrrole to pyrrole monomer used in the dispersing solvent. By varying this mole ratio, it is possible to create films ranging from monolayer to multilayer thicknesses. The most highly conducting films were produced with mole ratios of pyrrole to substituted pyrrole approaching 5000:1. Multilayers of these films were fabricated successfully by both the horizontal and the vertical lifting methods. The electrical and optical properties of these new films are discussed.

Formation of novel electrically conductive Langmuir–Blodgett multilayer thin films of poly(3-alkylthiophenes)

Langmuir–Blodgett multilayer thin films have been fabricated from mixed monolayers containing stearic acid and various poly(3-alkyl thiophenes); the resultant multilayer films exhibit well defined spacings, as indicated by X-ray diffraction, and can be chemically oxidized to produce electrically conductive multilayer thin films.

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.