Akif Kaynak

Electromagnetic shielding effectiveness of galvanostatically synthesized conducting polypyrrole films in the 300–2000 MHz frequency range

Both far-field (plane wave) and near field shielding effectiveness (SE) measurements have been conducted on electrochemically synthesized conducting polypyrrole (PPy) films with wide ranging conductivity levels (10−2 S/cm to 45 S/cm). Co-axial transmission line, TEM test cell and TE10 waveguide techniques were employed to measure shielding effectiveness as a function of polymer conductivity, frequency and temperature. Highly doped polypyrrole films exhibited shielding levels, above 40 dB from 300 MHz to 2 GHz, which can make them attractive for consideration in shielding applications. However, a loss of 10 to 15 dB in the shielding effectiveness, for the samples aged for a period of two years at room temperature, was observed. SE of PPy films increased with the increase in the dopant concentration and decreased with frequency reaching a plateau at higher frequencies. However, corrected SE values as a function of frequency appeared relatively flat. The measurements made directly on the TEM-t cell would simulate high impedance condition (E-field) due to the capacitive coupling, and use of the correction factors therefore eliminated this condition, giving rise to corrected far-field SE values. Using the theory for plane wave shielding effectiveness of thin material shields, the agreement between the theory and experimental results were tested. Effect of temperature on the plane-wave SE of a lightly doped (0.006 M p-TS) PPy film was also investigated. Results showed significant increase in the SE with temperature. At room temperature the lightly doped PPy film with a dc conductivity of 0.01 S/cm was almost transparent to microwaves with very little reflection or absorption. However as the temperature increased SE increased significantly because of the increase in conductivity of the sample.

Effect of synthesis parameters on the surface morphology of conducting polypyrrole films

Surface morphology of polypyrrole films was investigated by using atomic force and scanning electron microscopy techniques. Synthesis parameters such as dopant concentration and synthesis time and subsequent heat treatment were found to affect the surface morphology of electrochemically synthesized polypyrrole films. Mean height, root-mean-square roughness, and nodule diameter increased with increasing dopant concentration and synthesis time. Lightly doped, semiconducting films had smoother surface morphology with the mean height values as low as 500 A, whereas highly doped conducting films had dendritic surfaces with the mean height values of the nodules reaching several microns. At highest dopant concentrations and/or synthesis times exceeding 2 hours the film surface no longer resembled cauliflowers but a worm-like fibrillar morphology appeared. Fibrils started growing at a dopant concentration of 0.025 M and at 0.05 M the film surface was covered with fibrils with pointed tips.

Some microwave and mechanical properties of carbon fiber-polypropylene and carbon black-polypropylene composites

The insertion loss, return loss and electromagnetic shielding effectiveness of carbon-black and carbon-fiber-filled polypropylene composites were studied in the 8 to 12 GHz frequency range. Both electromagnetic and mechanical measurements were performed at various filler concentrations. The maximum shielding values obtained for carbon-fiber-filled composites was over 40 dB for 35 wt% concentration. Youngs modulus, ultimate strength and elongation at break with respect to filler concentration were also determined. The stiffness and brittleness of the composites increased with increasing filler concentration. The ultimate strength of the carbon-black-filled composites increased whereas the ultimate strength of carbon-fiber-filled composites decreased with the filler content. Elongation at break values for all composites dropped sharply with the filler concentration.

Characterization of Conductive Polypyrrole Coated Wool Yarns

Wool yarns were coated with conducting polypyrrole by chemical synthesis methods. Polymerization of pyrrole was carried out in the presence of wool yarn at various concentrations of the monomer and dopant anion. The changes in tensile, moisture absorption, and electrical properties of the yarn upon coating with conductive polypyrrole are presented. Coating the wool yarns with conductive polypyrrole resulted in higher tenacity, higher breaking strain, and lower initial modulus. The changes in tensile properties are attributed to the changes in surface morphology due to the coating and reinforcing effect of conductive polypyrrole. The thickness of the coating increased with the concentration of p-toluene sulfonic acid, which in turn caused a reduction in the moisture regain of the wool yarn. Reducing the synthesis temperature and replacing p-toluenesulfonic acid by anthraquinone sulfonic acid resulted in a large reduction in the resistance of the yarn.

Change of mechanical and electrical properties of polypyrrole films with dopant concentration and oxidative aging

The process of loss of mechanical and electrical properties of polypyrrole (Ppy) was studied for up to 12 months of aging in air at room temperature. Tensile strength of films highly doped with p-toluene sulphonate was lower than that of lightly doped ones. This difference is attributed to the presence of stress concentrations on the nodular surfaces of the films with high dopant concentrations. Highly doped films were electrically more stable, with a lower rate of loss of conductivity with time, compared with lightly doped ones. The conductivity of the latter initially decreased at a different rate than that observed after a prolonged time, exhibiting two regions in the aging behavior. In contrast, highly doped PPy films followed first-order kinetics with a very small loss of conductivity over the aging period. The rate of decline of conductivity was dependent on aging time, dopant type, and concentration, suggesting a complex mechanism of conductivity decay. Examination of FT-IR spectra of aged Ppy films revealed an increase in intensity of an α, β-unsaturated conjugated carbonyl peak, which may be correlated with the loss in conductivity.

Technical Review : Conducting Polymer Electronics

Before conducting polymers can be employed in many applications, some of the intrinsic properties of these materials need to be better understood. An overview of the research and development of conducting polymers being undertaken at UTS is presented. Because conducting polymers are difficult to process once fabricated, an understanding of synthesis parameters and the use of synthesis techniques to pro duce conducting polymer films with desired properties is of the upmost importance. Descriptions of the galvanostatic and potentiostatic techniques employed to produce polyheterocyclics are presented. Thermal properties such as thermal diffusivity, ther mal conductivity and specific heat are being investigated. Preliminary results reveal that the thermal diffusivity of polypyrrole is higher than that achieved with traditional polymers. The nature of contacts and junctions with polypyrrole and poly(3-methyl thiophene) are discussed. High work function metals form ohmic junctions with polypyr role while aluminium forms a Schottky barrier with poly(3-methylthiophene). Micro wave studies on polypyrrole films reveal that the microwave transmission and reflection are dependent upon the doping level of the film. Applications of the conducting polymers in data security modules and for light weight electrically conducting wires are also il lustrated.

Microwave transmission, reflection and dielectric properties of conducting and semiconducting polypyrrole films and powders

Microwave transmission, reflection and some dielectric properties of the conducting polymer, polypyrrole, are presented. Methods are discussed for determining microwave transmission and reflection of electrochemically synthesized and doped polypyrrole films with conductivities ranging from 0.1–5000 S m−1. Polypyrrole films were placed between waveguides and irradiated with microwaves centred at frequencies 2.45 and 10 GHz with 0.1 GHz span. The results indicate that the conductivity of doped polypyrrole films has a significant effect on both transmission and reflection. Microwave opacity of polypyrrole varied with the synthesis conditions of the polymer. Samples with low conductivity exhibited high transmission whereas low transmission readings were observed with highly conducting films. Dielectric properties are also presented for frequencies from 100 to 106 Hz in a temperature range of 90–280 K and at microwave frequencies of 2.45 and 10 GHz. These measurements indicate that the real and imaginary parts of the dielectric constant increase in magnitude with increasing doping level.

Developing lspr design guidelines

Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices

Frictional and tensile properties of conducting polymer coated wool and alpaca fibers

Wool and alpaca fibers were coated with polypyrrole by vapor-phase polymerisation method. The changes in frictional and tensile properties of the single fibers upon coating with the conductive polymer are presented. Coating a thin layer of polypyrrole on the alpaca and wool fibers results in a significant reduction in the fiber coefficient of friction, as the conducting polymer layer smooths the protruding edges of the fiber scales. It also reduces the directional friction effect of the fibers. Depending on the type of fiber, the coating may slightly enhance the tensile properties of the coated fibers.

Study of conducting polypyrrole films in the microwave region

Abstract Dielectric properties of the electrochemically synthesised polymer polypyrrole with a wide range of doping levels are presented. Methods for determining the complex dielectric constant in the microwave regime are discussed. The variation of the complex dielectric constant as a function of polymer dopant concentration at room temperature using cylindrical and rectangular cavity perturbation methods at frequencies of 2.45 GHz and 10 GHz is presented. Measurements indicate that the real and imaginary parts of the dielectric constant increase in magnitude with increasing polymer doping level. Complex dielectric constant measurements were continued on semiconducting polypyrrole films with a dc conductivity range of 1×10 −3 −5×10 −2 S/cm for the temperature range 90K–300K. The real part e′ of the complex dielectric constant increased slightly with increase of temperature whereas the imaginary part e″ increased significantly with temperature. The rate of change of the dielectric loss increased with temperature and the magnitude of the loss at a given temperature increased with increasing polymer doping levels. Reflection, transmission and absorption behaviour of polypyrrole films with dc conductivities ranging from 0.001 S/cm to 50 S/cm are also presented. Results indicate that conductivity of the doped polypyrrole films have a significant effect on transmission, reflection and absorption of microwaves. Samples with low conductivity (low dopant concentration) exhibited high transmission whereas highly conducting films were reflective. Significant absorption of microwave radiation was only observed for samples of intermediate conductivity. Solutions by theoretical methods were in good agreement with the experimentally measured results from the polypyrrole films and hence confirm the dependability of the dielectric measurement method used.