Electromagnetic shielding properties of polypyrrole/polyester composites in the 1–18 GHz frequency range

The dielectric characteristics of conducting polymer-coated textiles in the frequency range 1–18 GHz were investigated using a non-contact, non-destructive free space technique. Polypyrrole coatings were applied by solution polymerization on fabric substrates using a range of concentrations of para-toluene-2-sulfonic acid (pTSA) as dopant and ferric chloride as oxidant. The conducting polymer coatings exhibited dispersive permittivity behaviour with a decrease in real and imaginary components of complex permittivity as frequency increased in the range tested. Both the permittivity and the loss factor were affected by the polymerization time of the conductive coating. It was found that the total shielding efficiency of these conductive fabrics is significant at short polymerization times and increases to values exceeding 80% with longer polymerization times. The reflection contribution to electromagnetic shielding also increases with polymerization time.

Electromagnetic interference shielding and radiation absorption in thin polypyrrole films

Results of permittivity measurements, electromagnetic interference shielding effectiveness, and heat generation due to microwave absorption in conducting polymer coated textiles are reported and discussed. The intrinsically conducting polymer, polypyrrole, doped with anthraquinone-2-sulfonic acid (AQSA) or para-toluene-2-sulfonic acid (pTSA) was applied on textile substrates and the resulting materials were investigated in the frequency range 1–18 GHz. The 0.54 mm thick conducting textile/polypyrrole composites absorbed up to 49.5% of the incident 30–35 W microwave radiation. A thermography station was used to monitor the temperature of these composites during the irradiation process, where absorption was confirmed via visible heat losses. Samples with lower conductivity showed larger temperature increases caused by microwave absorption compared to samples with higher conductivity. A sample with an average sheet resistivity of 150 Ω/sq. showed a maximum temperature increase of 5.27 °C, whilst a sample with a lower resistivity (105 Ω/sq.) rose by 3.85 °C.

Stress-shielding as a cause of insertional tendinopathy: the operative technique of limited adductor tenotomy supports this theory

The aetiology of tendinopathy is poorly understood. A new hypothesis proposed argues that tendinopathy may not be purely a tensile injury, rather that altered mechanics such as compression or stress-shielding may be important. Both tendon compression and a decrease in tendon load (stress-shielding) will induce change in a tendon similar to that seen in an insertional tendinopathy.

Stress-shielding as a cause of tendinopathy is supported by the clinical success of operative release of adductor longus. This surgery releases the superficial section of the normal adductor longus tendon at a point distal to the insertion. This may have the effect of transferring stress from the superficial section of the tendon to the stress-shielded deeper portion, and the induction of normal loads in both the deeper and superficial portions of the tendon may assist in tendon recovery. This interesting hypothesis and clinical intervention require further investigation

UV-shielding ceramic nanoparticles synthesised by mechanochemcial processing

ZnO, TiO₂ and CeO₂ are known as UV-shielding ceramic materials that have advantages over organic UV absorbers for their photo-stability and non-hazardous nature to human bodies. However, they normally cause low transparency in the visible-light range due to light scattering by large particles, which is undesirable for many transparent UV-blocking applications in cosmetic and plastic industries. Light-scattering efficiency of particles can be drastically reduced by decreasing the particle sizes down below 100 nm. This paper reviews recent investigation on the synthesis of ZnO and CeO₂ nanoparticles by mechanochemical processing. The resulting particles had a significantly low degree of agglomeration, having mean particle sizes of ~ 25 nm and ~ 10 nm, respectively. The aqueous suspensions of the nanoparticles showed strong absorption in the UV-light range and high transmittance in the visible-light range. Mechanochemical processing offers the possibility of industrial-scale production of transparent UV-shielding ceramic particles for many applications.

Transparent uv-shielding films from organic small molecule-intercalated layered double hydroxide nanoplatelets/polymer composite

In this study, layered double hydroxide (LDH) with nitrate as the interlayer anion has been partially exfoliated in dimethyl sulfoxide (DMSO). Atomic force microscopy (AFM) images showed that both the lateral size and the thickness of the LDH nanoplatelets were decreased after DMSO treatment. Formation of transparent LDH suspension in DMSO was observed. Taking this advantage, we have prepared transparent LDH/ethylene-vinyl alcohol copolymer (EVOH) nanocomposite films using DMSO as the processing solvent. Organic small molecules, UV absorbers, were intercalated into the LDH interlayers to incorporate the UV-shielding property into the transparent composite films. The thermal stability of UV absorbers was considerably improved after intercalation, which was attributed to the electrostatic interaction between the guest UV absorbers and the host LDH layers. The prepared composite films were flexible and exhibited excellent UV-shielding capability, but had transmittance as high as 90% in the visible region. The effect of LDH filler on thermal and mechanical properties of the composite films was also examined.

A review of techniques for the monitoring of cathodic shielding and corrosion under disbonded coatings

The mitigation of external corrosion of energy pipelines by a combination of barrier coatings and Cathodic Protection (CP) is not always effective. Even when design specifications are properly met, the shielding of cathodic protection current from reaching steel surface by disbonded barrier coatings, often referred to as cathodic shielding, may lead to severe corrosion problems such as deep pitting, high and near neutral pH Stress Corrosion Cracking (SCC) and Microbiologically Induced Corrosion (MIC). Unfortunately, current indirect assessment methods used in the pipeline industry have serious difficulties in detecting such corrosion problems. This paper provides a brief review of current techniques and their limitations when being applied under complex buried pipeline environmental conditions. The main purpose is to identify potential methods that could be utilised in the design of new monitoring probes specific for the monitoring of cathodic shielding and corrosion of disbonded coatings in the pipeline industry.

Monitoring cathodic shielding and corrosion under disbonded coatings

This work presents a novel corrosion monitoring probe designed for simulating the conditions developed under disbonded coatings and for measuring current densities and their distribution over a simulated pipeline surface. The probe’s concept was experimentally evaluated via immersion tests under Cathodic Protection (CP) in high resistivity aqueous solution. Under the disbonded area, anodic currents as well as cathodic currents were both measured. Anodic current densities were used to calculate metal losses by means of Faraday’s law. Calculated corrosion patterns were compared with corrosion damage observed at the probe’s surface after a period of test. The probe’s working principles are explained in terms of simple electrochemistry.

Aging studies on conducting polypyrrole

Change of tensile properties, electrical conductivity and microwave shielding of electrochemically synthesized polypyrrole films with time are presented. Highly doped films had good electrical stability, retaining high microwave reflectivity throughout the aging period. Lightly doped films were less stable and partially reflective and absorptive of microwaves. FT-IR spectral observations revealed a progressive increase in intensity of an unsaturated conjugated carbonyl peak, which was not observed in the highly doped films, suggesting that the concentration of the dopant had an influence on the mechanism of degradation of conductivity.

Secondary bonding in para-substituted diphenyltellurium dichlorides (p-XC6H4)2TeCl2 (X = H, Me, MeO) probed by 125Te MAS NMR spectroscopy. Crystal and molecular structure of (p-MeC6H4)2TeCl2

The solid-state structures of the previously known para-substituted diphenyltellurium dichlorides, (p-XC₆H₄)₂TeCl₂ (X=H (1), Me (2), MeO (3)) were investigated by ¹²⁵Te MAS NMR spectroscopy and in case of 2 by single crystal X-ray diffraction. The ¹²⁵Te-NMR shielding anisotropy (SA) was studied by tensor analyses based on relative intensities of the observed spinning sidebands. Solid-state NMR parameters, namely the isotropic chemical shift (δ_iso), anisotropy (ζ) and asymmetry (η), were discussed in relation to the molecular structures established by X-ray crystallography. The asymmetry (η) was found to be particularly sensitive to structural differences stemming mostly from the diverse secondary Te...Cl interactions, but no correlation with geometric parameters could be established.

Conductive fabrics for heating applications

By coating textiles with electrically conductive organic polymers, we are able to produce functional, intelligent fabrics. These fabrics can be utilised in applications such as gas sensors, actuators, electromagnetic shielding, radar absorption, selected frequency filtering in indoor wireless applications, and heating applications where vital parts of the body can be heated without embedding any wiring through the fabric.

Heat generation in fabrics coated with the conductive polymer polypyrrole was investigated. The fabrics were coated by chemical synthesis methods by oxidizing the pyrrole monomer in the presence of the fabric substrate. Ferric chloride was selected as the oxidizing agent and anthraquinone-2-sulfonic acid (AQSA) sodium salt monohydrate as the dopant.

Conductive fabrics were characterized by resistivity measurements, scanning electron microscopy, thermal imaging, current transmission over a period of time and calculations of power density per unit area. Effects of reaction conditions on the electrical properties and heat generated are presented. Polypyrrole coated fabrics were stable and possessed high electrical conductivity. Resistivity values ranged from 100-500 ohms/square depending on the reaction parameters. When subjected to a constant voltage of 24V, the polypyrrole coated polyester-Lycra® fabric doped with AQSA reached a maximum temperature of 42°C and a power density per unit area of 430 W/m² was achieved.

Dielectric characterization of conducting textiles using free space transmission measurements: accuracy and methods for improvement

The dielectric behaviour of in-situ polymerized thin polypyrrole (PPy) films on synthetic textile substrates were obtained in the 1–18 GHz region using free space transmission and reflection methods. The PPy/para-toluene-2-sulphonic acid (pTSA) coated fabrics exhibited an absorption dominated total shielding effectiveness (SE) of up to −7.34 dB, which corresponds to more than 80% of incident radiation. The permittivity response is significantly influenced by the changes in ambient conditions, sample size and diffraction around the sample. Mathematical diffraction removal, time-gating tools and high gain horns were utilized to improve the permittivity response. A narrow time-gate of 0.15 ns produced accurate response for frequencies above 6.7 GHz and the high gain horns further improved the response in the 7.5–18 GHz range. Errors between calculated and measured values of reflection were most commonly within 2%, indicating good accuracy of the method.

Natural and environmentally responsive building envelopes

In a context of global warming and our needs to reduce CO\d2 emissions, building envelopes will play an important role. A new imperative has been put forth to architects and engineers to develop innovative materials, components and systems, in order to make building envelopes adaptive and responsive to variable and extreme climate conditions. Envelopes serve multiple functions, from shielding the interior environment to collecting, storing and generating energy. Perhaps a more recent concern of terrestrial habitats is permeability and leakages within the building envelope. Such airtight and concealed envelopes with zero particle exchange are a necessity and already exist in regard to space capsules and habitats.

This paper attempts to acknowledge existing and visionary envelope concepts and their functioning in conjunction with maintaining a favorable interior environment. It introduces several criteria and requirements of advanced fa\acades along with interior pressurization control. Furthermore, the paper also takes a closer look at the principles of "biomimicry" of natural systems combined with the most up-to-date building materials and construction technologies, trying to integrate the notions of adaptation - where the capacity to survive depends on the ability to adjust to the environment - within the concept of technological evolution and innovation. An "adaptive" attitude in the way in which we conceive our built structures provides a conceptual basis for the advanced building design of our future, as well as one concerned about the efficient management of the available resources. Built environments of the future (in extreme climates or not) will need to respond to Renewable, Adaptive, Recyclable and Environmental (R.A.R.E.) concepts in order to coexist in a sustainable way with their surroundings.