Abstract
Smart textiles have properties that outperform the conventional protective and decorative function of textiles. By integrating special sensors into clothing, body functions and movements can be detected. Piezoresistive sensors measure a change in electrical resistance due to the application of force in the form of stretching, pressure or bending. In order to manufacture such sensors, conventional non-conductive textile materials need to be made conductive by finishing processes. Therefore, a non-conductive silicone monofilament was coated with a conductive carbon silicone and additional silver-containing components and investigated for its suitability as a strain sensor. The changes in electrical resistance and the gauge factor as a measure of the sensitivity of a sensor were measured and calculated. In this publication, the electrical properties of such a filament-based sensor in the context of particle composition and concentration are discussed. The electrical resistance was already significantly reduced in a first step by coating with conductive carbon silicone (145 kΩ). The addition of silver-containing components further reduced the electrical resistance in a second step. Thereby, flat flakes of silver proved to be much more effective than silver-containing particles (5 kΩ at 20% addition). The former was easier to integrate into the coating and formed contact surfaces with each other at higher concentrations. Stretching the samples increased the resistance by enlarging the distance between the conductive components. With 30% silver-coated glass flakes in the coating, the highest gauge factor of 0.33 was achieved. Consequently, the changes in electrical resistance during stretching can be exploited to detect motion and the gauge factor indicates that even small changes in strain can be detected, so the herein developed coated monofilaments are suggested for use as strain sensors. Future work includes matching the particle composition and concentration to the exact application and investigating the sensors in the field.
Highlights
The monitoring of various bodily functions and movements is an important field of application for smart textiles
The changes in electrical resistance during stretching can be exploited to detect motion and the gauge factor indicates that even small changes in strain can be detected, so the developed coated monofilaments are suggested for use as strain sensors
Monofilaments made of silicone are not suitable for the production of piezoresistive sensors due to their insulator properties
Summary
The monitoring of various bodily functions and movements is an important field of application for smart textiles. In order to measure the change in electrical resistance as a function of strain, a conductive material must be present. Since conventional polymers used for textiles are not sufficiently conductive, they must be modified by adding or integrating conductive material, which is referred to as extrinsic conductivity This can be achieved, for example, by coating them with conductive coatings or integrating conductive fillers, such as carbon black [7,13,14,15], carbon nanotubes [16], or metallic additives [17,18,19] into the polymer matrix. The size and shape of the added fillers influence the filler density and the conductivity [21,23,24]
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