Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

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An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film

A novel carbon nanotube-polystyrene foam composite has been fabricated successfully. The electromagnetic interference (EMI) shielding effectiveness measurements indicated that such foam composites can be used as very effective, lightweight shielding materials. The correlation between the shielding effectiveness and electrical conductivity and the EMI shielding mechanism of such foam composites are also discussed.

Novel carbon nanotube-polystyrene foam composites for electromagnetic interference shielding.

By using computer image processing and analysis, a system to detect both weave patterns and yarn color designs is developed in this study. The image of a woven fabric is captured by a Hitachi color CCD camera and converted into digital data by a Targa+32 board. Two images—transmitted and reflected—are used to detect weave patterns. From the transmitted images, warp and weft cross points and the sizes of the yarns are determined by analyzing gray value changes in both horizontal and vertical directions. Then the warp and weft crossed states are determined by analyzing the normalized aspect ratio of an ellipse-shaped image at crossed points of the fabric. Furthermore, from reflected images, the total number of yarn colors and their arrangements in the fabric are determined. An HSV color model differentiates or groups similar yarn colors. Consequently, the system allows the weave pattern, either colored or solid, and the color design of a fabric to be correctly recognized.

Automatic Recognition of Fabric Weave Patterns by Digital Image Analysis

Electromagnetic interference shielding effectiveness of electroless Cu-plated PET fabrics

Changes in conductivity with repeated fabric extension were investigated to improve the properties of conductive electrode pad material used for electrotherapy when it is subjected to various movement of human body. Highly stretchable and conductive fabrics were prepared by in situ chemical polymerization of polypyrrole on nylon–spandex stretch fabric in aqueous solutions with 0.5 M pyrrole, 1.165 M FeCl3, and 0.165 M benzenesulfonic acid at 5°C for 1 h. Performance of prepared stretchable conductive fabric was evaluated in terms of conductivity changes as a function of tensile strain, repeated extension, and current application time. As the degree of extension increased, the conductivity increased and leveled off when the fabric was subjected to 60% extension. The number of fiber contacts in nylon–spandex fabric with electrode increased as the applied extension increased. However, the conductivity of the composite decreased under excessive extension over 60% since the intrinsic elasticity of fabric became gradually reduced. Generally, the fabric conductivity decreased as the number of extension cycles increased. However, the fabric conductivity was well maintained after repeated extension over 30 cycles at 40% extension. In addition, it was found that the effect of charging during the electrotherapy treatment on a current flow through prepared electrode pad was negligible. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1225–1229, 2003

Stretchable conductive fabric for electrotherapy

Protein based scaffolds are preferred for tissue engineering and other biomedical applications owing to their unique properties. Zein, a hydrophobic protein, is a promising natural biodegradable polymer. However, electrospun structures prepared from Zein have poor mechanical and wetting properties. Cellulose acetate (CA) is an economical, biodegradable polymer having good mechanical and water retention properties. The aim of present study was to fabricate a novel material by electrospinning Zein/CA blends. A series of Zein/CA hybrid nanofibers were electrospun and characterized. The attenuated total reflectance-Fourier transform infrared spectroscopy (ATRFTIR) spectrum showed the characteristic peaks of both Zein and CA, and was composition dependent. The X-ray photoelectron spectrometry (XPS) curves of Zein/CA blends demonstrated a similar profile to that of pristine Zein nanofibers. Thermogravimetric analyser (TGA) studies confirmed that the Zein/CA hybrid nanofibers have a higher degradation temperature and better thermal stability than pristine Zein nanofibers. The glass transition temperature (T
 g
 ) of Zein/CA hybrid nanofibers was also increased in comparison to pure Zein nanofibers as revealed by differential scanning calorimetry (DSC). Zein/CA hybrid nanofibers have hydrophilic surface character as revealed by water contact angle (WCA) analysis. SEM imaging showed bead free morphology of the electrospun nanofibers. The average nanofiber diameter decreased for Zein/CA blends with increasing CA composition. The electrospun Zein/CA hybrid nanofibers may be used for tissue engineering scaffolds and for other biomedical materials.

Zein/cellulose acetate hybrid nanofibers: Electrospinning and characterization

Ultra porous and flexible PET/Aerogel blankets were prepared at ambient pressure, and their acoustic and thermal insulation properties were characterized. Two methods were selected for the preparation of PET/Aerogel blanket. Method I was a direct gelation of silica on PET. PET non-woven fabric was dipped and swelled in TEOS/ethanol mixture, and pH of reaction media was controlled to 2.5 using HCl to promote hydrolysis. After acid hydrolysis, pH was controlled to 7,8,9, and 10 with NH4OH for the condensation. Method II was by the dipping of PET non-woven fabric in the dispersion of Silica hydrogel. The gelation process was same with Method I. However, PET fabric was not dipped in reaction media. After the hydrogel was dispersed and aged in EtOH for 24 hrs, then, PET non-woven fabric was dipped in the dispersion of hydrogel/EtOH for 24 hrs. The surface modification was carried out in TMCS/n-hexane solution, then the blanket was washed with nhexane and dried at room temperature to prevent the shrinkage. The silica areogels synthesized in optimum conditions exhibit porous network structure. Silica aerogel of highly homogeneous and smallest spherical particle clusters with pores was prepared by gelation process at pH 7. When direct gelation of silica was performed in PET nonwoven matrix (Method I), silica aerogel clusters were formed efficiently surrounding PET fibers forming network structure. The existence of a great amount of silica aerogel of more homogeneous and smaller size in the cell wall material has positive effect on the sound absorption and thermal insulation.

Kyung Wha Oh

Papers

Automatic Recognition of Fabric Weave Patterns by Digital Image Analysis

Electromagnetic interference shielding effectiveness of electroless Cu-plated PET fabrics

Stretchable conductive fabric for electrotherapy

Zein/cellulose acetate hybrid nanofibers: Electrospinning and characterization

Ultra-porous flexible PET/Aerogel blanket for sound absorption and thermal insulation