Abstract
Complex permittivity of conducting polypyrrole (PPy)-coated Nylon-Lycra textiles is measured using a free space transmission measurement technique over the frequency range of 1–18 GHz. The aging of microwave dielectric properties and reflection, transmission and absorption for a period of 18 months is demonstrated. PPy-coated fabrics are shown to be lossy over the full frequency range. The levels of absorption are shown to be higher than reflection in the tested samples. This is attributed to the relatively high resistivity of the PPy-coated fabrics. Both the dopant concentration and polymerisation time affect the total shielding effectiveness and microwave aging behaviour. Distinguishing either of these two factors as being exclusively the dominant mechanism of shielding effectiveness is shown to be difficult. It is observed that the PPy-coated Nylon-Lycra samples with a p-toluene sulfonic acid (pTSA) concentration of 0.015 M and polymerisation times of 60 min and 180 min have 37% and 26% decrease in total transmission loss, respectively, upon aging for 72 weeks at room temperature (20 °C, 65% Relative humidity (RH)). The concentration of the dopant also influences the microwave aging behaviour of the PPy-coated fabrics. The samples with a higher dopant concentration of 0.027 mol/L pTSA are shown to have a transmission loss of 32.6% and 16.5% for short and long polymerisation times, respectively, when aged for 72 weeks. The microwave properties exhibit better stability with high dopant concentration and/or longer polymerization times. High pTSA dopant concentrations and/or longer polymerisation times result in high microwave insertion loss and are more effective in reducing the transmission and also increasing the longevity of the electrical properties.
Highlights
Conducting polymers such as polypyrrole and polyaniline, when used in conjunction with suitable substrates, exhibit high radiation absorption and shielding in the microwave frequency region [1,2].Wide-ranging modulation of electrical and electromagnetic properties of conducting polymer films can be utilised effectively when they are coated on flexible and strong substrates such as textiles.The intricate structures and fibrous surfaces of textiles enable deep penetration of the polymer into the interstices of the flexible fibre assemblies
The degradation or chemical aging causes an increase in the electrical resistivity which in turn changes the nature of the interaction of the material with electromagnetic waves and manifests as changes in the complex permittivity, microwave reflection, transmission and absorption behaviour in conductive polymer films and conductive textiles
We present the complex permittivity of conducting polypyrrole (PPy)-coated Nylon-Lycra textiles by using a free space transmission measurement technique over the frequency range 1–18 GHz and report the changes in permittivity and transmission losses over a period of 72 weeks at room temperature
Summary
Conducting polymers such as polypyrrole and polyaniline, when used in conjunction with suitable substrates, exhibit high radiation absorption and shielding in the microwave frequency region [1,2].Wide-ranging modulation of electrical and electromagnetic properties of conducting polymer films can be utilised effectively when they are coated on flexible and strong substrates such as textiles.The intricate structures and fibrous surfaces of textiles enable deep penetration of the polymer into the interstices of the flexible fibre assemblies. Conducting polymers such as polypyrrole and polyaniline, when used in conjunction with suitable substrates, exhibit high radiation absorption and shielding in the microwave frequency region [1,2]. Wide-ranging modulation of electrical and electromagnetic properties of conducting polymer films can be utilised effectively when they are coated on flexible and strong substrates such as textiles. Conducting polymers possess wide-ranging electrical resistivity and electromagnetic reflective and absorptive properties that can be controlled during the polymerisation stage, by the type and concentrations of the monomer, dopant, oxidant, solvent, Materials 2016, 9, 609; doi:10.3390/ma9070609 www.mdpi.com/journal/materials. The degradation or chemical aging causes an increase in the electrical resistivity which in turn changes the nature of the interaction of the material with electromagnetic waves and manifests as changes in the complex permittivity, microwave reflection, transmission and absorption behaviour in conductive polymer films and conductive textiles. The degradation in conducting polymers upon aging was mainly attributed to oxygen attack and the formation of carbonyl species in the polymer backbone [5], but heat, light, mechanical stress, ozone, moisture and atmospheric pollutants contributed [6]
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