Piezoelectric coaxial filaments produced by coextrusion of poly(vinylidene fluoride) and electrically conductive inner and outer layers

Piezoelectric Fibers: Processing and Challenges

Integration of piezoelectric materials in composite and textile structures is promising for creating smart textiles with sensing or energy harvesting functionalities. The most direct integration that combines wearability, comfort, and piezoelectric efficiency consists of using fibers made of piezoelectric materials. The latter include inorganic ceramics or organic polymers. Ceramics have outstanding piezoelectric properties but can not be easily melted or solubilized in a solvent to be processed in the form of fibers. They have to be spun from precursor materials and thermally treated afterward for densification and sintering. These delicate processes have to be carefully controlled to optimize the piezoelectric properties of the fibers. On the other hand, organic piezoelectric polymers, such as polyvinylidene fluoride (PVDF), can be spun by more conventional textile fibers technologies. In addition to enjoy an easier manufacturing, organic piezoelectric fibers display flexibility that facilitates their integration and use in smart textiles. However, organic fibers suffer from a low piezoelectric efficiency. This reviews looks at the processing techniques and their specific limitations and advantages to realize single-component or coaxial piezofibers. Fundamental challenges related to the use of composite fibers are discussed. The latter include challenges for poling and electrically wiring the fibers to collect charges under operation or to apply electrical fields. The electromechanical properties of these fibers processed by different manufacturing techniques are compared. Recent studies of structures used to integrate such fibers in textiles and composites with conventional techniques and their potential applications are discussed.

High-performance coaxial piezoelectric energy generator (C-PEG) yarn of Cu/PVDF-TrFE/PDMS/Nylon/Ag

Coaxial type piezoelectric energy generator (C-PEG) nanofiber was fabricated by a self-designed continuous electrospinning deposition system. Piezoelectric PVDF-TrFE nanofiber as an electroactive material was electrospun at a discharge voltage of 9-12 kV onto a simultaneously rotating and transverse moving Cu metal wire at an angular velocity of ω _g = 60-120 RPM. The piezoelectric coefficient d₃₃ of the PVDF-TrFE nanofiber was approximately -20 pm V^-1. The generated output voltage (V _G) increased according to the relationship exp(-α P) (α = 0.41- 0.57) as the pressure (P) increased from 30 to 500 kpa. The V _G values for ten and twenty pieces of C-PEG were V _G = 3.9 V and 9.5 V at P = 100 kpa, respectively, relatively high output voltages compared to previously reported values. The high V _G for the C-PEG stems from the fact that it can generate a fairly high V _G due to the increased number of voltage collection points compared to a conventional two-dimensional (2-dim) capacitor type of piezoelectric film or fiber device. C-PEG yarn was also fabricated via the dip-coating of a PDMS polymer solution, followed by winding with Ag-coated nylon fiber as an outer electrode. The current and power density of ten pieces of C-PEG yarn were correspondingly 22 nA cm^-2 and 8.6 μW cm^-3 at V _G = 1.97 V, higher than previously reported values of 5.54 and 6 μW cm^-3. The C-PEG yarn, which can generate high voltage compared to the conventional film/nanofiber mat type, is expected to be very useful as a wearable energy generator system.

E-Knitted Textile with Polymer Optical Fibers for Friction and Pressure Monitoring in Socks

The objective of this paper is to study the ability of polymer optical fiber (POF) to be inserted in a knitted fabric and to measure both pressure and friction when walking. Firstly, POF, marketed and in development, have been compared in terms of the required mechanical properties for the insertion of the fiber directly into a knitted fabric on an industrial scale, i.e. elongation, bending rigidity, and minimum bending radius before plastic deformation. Secondly, the chosen optical fiber was inserted inside several types of knitted fabric and was shown to be sensitive to friction and compression. The knitted structure with the highest sensitivity has been chosen for sock prototype manufacturing. Finally, a feasibility study with an instrumented sock showed that it is possible to detect the different phases of walking in terms of compression and friction.

Piezoelectric Microstructured Fibers via Drawing of Multimaterial Preforms

We demonstrate planar laminated piezoelectric generators and piezoelectric microstructured fibers based on BaTiO₃-polyvinylidene and carbon-loaded-polyethylene materials combinations. The laminated piezoelectric generators were assembled by sandwiching the electrospun BaTiO₃-polyvinylidene mat between two carbon-loaded-polyethylene films. The piezoelectric microstructured fiber was fabricated via drawing of the multilayer fiber preform, and features a swissroll geometry that have ~10 alternating piezoelectric and conductive layers. Both piezoelectric generators have excellent mechanical durability, and could retain their piezoelectric performance after 3 day’s cyclic bend-release tests. Compared to the laminated generators, the piezoelectric fibers are advantageous as they could be directly woven into large-area commercial fabrics. Potential applications of the proposed piezoelectric fibers include micro-power-generation and remote sensing in wearable, automotive and aerospace industries.