Wearable systems, multifunctional materials and flexible structures

Abstract

Triboelectricity is a natural phenomenon, which had been considered to cause only negative results until some years ago. Wide research has been applied over the last decade to use it positively, mainly in energy harvesting and monitoring sensors. But most of the interest has focused on its novel applications than on how it exactly works. The integration of textiles in these novel applications makes them more promising as they can provide large surface areas and continuous activation thanks to the lasting movement of the wearer, while on the other hand, they can offer flexibility, elasticity, breathability, robustness etc to the final product. No matter if their electric outputs are lower than the ones of complicated materials and sophisticated structures, they can be used efficiently in signal sensoring or low energy demanding electronic parts. The understanding of how textile structures can perform in the triboelectric phenomenon is the foundation to develop their efficiency. This raises an interest due to the special characteristics of textiles, in a period that a lot of research is applied on the development of light, flexible and wearable triboelectric generators used for energy harvesting or self-powered sensors. But parameters related to the electrical outcomes of the textile structures, like the contact time duration of the fabrics, the force applied between the fabrics, the effective contact depending on the direction and orientation of the fabrics surfaces and the structure’s surface pattern has not been studied thoroughly. Thus it would be necessary to reproduce the phenomenon in a real environment under controllable conditions and make the appropriate tests. Considering all the above facts, plus the absence of a standard method to be used for the study or comparison of the triboelectric behaviour of textile structures, the need for building a prototype testing device has risen. This was designed and developed based on the vertical contact-separation mode, to allow us to measure different samples under the same conditions or the same sample under different conditions. Textile fabric samples were paired and tested. A small similarity on the voltages was noticed between reverse orientations of the samples surfaces, meaning between 0o and 180o, and between -90o and 90o, which might be caused by the different surface contact of the paired fabrics due to the warps and wefts presence. Moreover, an increase of the voltage values with the increase of the contact force between the textile fabric samples surfaces was found, when using certain samples which give significant electric outputs. It was also previewed that the contact duration does not affect the selected samples output voltage and that the surface pattern of a textile fabric can be of major importance for its triboelectric outcomes.