Jerzy J. Langer

N-substituted polyanilines: II. Photoacoustic and FT-IR spectra of poly(N-methylaniline) and related copolymers

Abstract Photoacoustic and FT-IR spectra of poly(N-methylaniline) and copolymers were measured and some surprising observations concerning the differences between them are discussed.

N-substituted polyanilines: I. Poly(N-methylaniline) and related copolymers

Abstract The electrical conductivity of poly(N-methylaniline) and copolymers obtained by anodic oxidation of N-methylaniline (NMA) and mixtures of NMA with aniline of controlled composition was measured over a wide temperature range. The essential role of protons and hydrogen bonding in the intermolecular coupling and the charge transport has been found.

Conformations of aniline black (polyaniline) molecules

Abstract Conformations of aniline black molecules were studied using a semi-empirical computer-aided analysis. A strong deformation of the ‘planar structure’ of the molecules has been found.

Polyaniline micro- and nanofibrils

Micro- and nanofibril structures have been found in polyaniline (PANI) doped with [60]fullerene. The fibrils of a thickness from 10 nm to 100 nm are usually as long as 3000 nm. In the extreme case fibrils, resembling PANI microrods reported previously, reach a diameter of 300 nm or more and the length much above 3000 nm. The samples were prepared either as a bulk material and thin layers. The materials as bulk samples were characterised with EPR, FTIR, cyclic-voltammetry and electrical conductivity measurements and details of the micro- and nano-structure were examined with the aid of a Philips scanning electron microscope (SEM). The results of the computer modelling have also been discussed.

A process leading to the domain structure of aniline black (polyaniline)

Abstract Proton-diffusion controlled self-oxidation (disproportionation) of the emeraldine form of polyaniline is proposed to explain the mechanism of a process leading to the domain structure of aniline black. The electrical conductivity calculated (5–6 S/cm) using EMT for the model structure considered is very close to values measured experimentally by other research workers (1–5 S/cm).

An Efficient 3D Cell Culture Method on Biomimetic Nanostructured Grids

Current techniques of in vitro cell cultures are able to mimic the in vivo environment only to a limited extent, as they enable cells to grow only in two dimensions. Therefore cell culture approaches should rely on scaffolds that provide support comparable to the extracellular matrix. Here we demonstrate the advantages of novel nanostructured three-dimensional grids fabricated using electro-spinning technique, as scaffolds for cultures of neoplastic cells. The results of the study show that the fibers allow for a dynamic growth of HeLa cells, which form multi-layer structures of symmetrical and spherical character. This indicates that the applied scaffolds are nontoxic and allow proper flow of oxygen, nutrients, and growth factors. In addition, grids have been proven to be useful in in situ examination of cells ultrastructure.

Fullerene-doped polyaniline

Polyaniline (PANI) doped with [60]fullerene has been prepared by electrochemical method (an aqueous medium at pit ∼1) in a copolymerisation process of aniline and o-, m- and p-aminobenzylamine-C 60 derivatives. The electrical conductivity of PANI with covalently bonded fullerene units is of 10 -2 S/cm and it depends on the temperature with activation energy of 0.002 eV and 0.068 eV, below 200 K and above 275 K, respectively. [60]fullerene units have also been incorporated into polyaniline network by the reaction of PANI macromolecules with hexanitro[60]fullerene. This results in an increase of the electrical conductivity, e.g. from 1 * 10 -3 S/cm to 4.1 * 10 -2 S/cm, while the activation energy does not change so much (0.078 eV above 275 K) except for a low temperature range (0.02 eV below 200 K). Similarly, we have observed a broadening of the EPR signal, changes in FTIR spectra and cyclic-voltammograms. The samples were prepared either as thin layers and a bulk material. In most cases, micro- and nanofiher structures have been observed with SEM.

Polyaniline fractals — a computer modelling

Abstract Computer simulations have been applied to study the fractal growth of polyaniline (PANI) microrods during the electrochemical polymerization. Formation of PANI microrods and their fractal structure can be explained as a kinetic effect well described within a modified diffusion-limited aggregation (DLA) model presented in this work. Microrods, if branched, form the angles of 60° or 120° and their fractal dimension df is about 1.7, as predicted with DLA model based on a random motion of aggregating molecules. PANI nano-structure is also fractal in nature. The fractal dimension df (about 1.9) and the form of fractals observed are comparable to those generated by a computer within our modified DLA model with a probability of aggregation dependent on the electrical conductivity and the structure of a macromolecule (aggregate) formed.

Non-linear optical effects (SRS) in nanostructured polyaniline LED

Non-linear optical effects (the stimulated anti-Stokes Raman scattering, SRS) have been observed in a nano-structured polyaniline LED. The mechanism of the anomalous enhancement is based on changes of the Raman cross section due to the resonant interaction involving stretching vibrations of triple bonds – diacetylene units, formed under strong excitation conditions in degradated polyaniline molecules, which are highly efficient in normal Raman scattering and SRS active. This is the first observation of SRS in a conducting polymer LED.

Laser action induced in a nanostructured polyaniline LED

Direct electrical pumping of polymer lasers is considered to be a great challenge. Our recent experiments indicate the laser action in a nanostructured polyaniline diode. This has been identified as an electrically pumped random laser, in which a conducting polymer (nanostructured polyaniline) plays the role of an active medium. The device of a simple LED architecture is directly electrically powered at a low voltage of 5–15 V. Above the threshold voltage (4–8 V) and the electrical energy pumped (75–100 W), different laser modes are generated, including the emission of nearly monochromatic light. This is the first electrically pumped random laser, based on a nanostructured conductive polymer – polyaniline. These results are groundbreaking in the field of polymer lasers, which are directly electrically powered. The impact of the findings is not limited either to this particular device or to the specific material used.