By embedding ultrathin, flexible and (ideally transparent) sensors, actuators, electronics and nanogenerators into textiles it becomes possible to develop a new generation of self-powered e-textiles where the electronic components are all but invisible. The resulting smart garments, smart medical attachments, data gloves and other human-machine interfaces will herald a new era of wearable electronics.
However, the electronic components in e-textiles are prone to short-circuits, rust and mechanical degradation due to natural flexibility and tendency of natural fibres (such as cotton of wool) to absorb moisture from the environment or the user. This moisture not only damages textile-based electronics but contributes to bacterial proliferation, making the textile smelly and uncomfortable to wear. There are also problems caused by putting e-textiles into washing machines.
Thanks to new work coming out of Purdue University, it is now possible to fabricate textiles that can protect you from rain, stains and bacteria while they harvest the biomechanical energy of the user to power textile-based electronics.
These self-powered e-textiles also constitute an important advancement in the development of wearable machine-human interfaces, which now can be washed many times in a conventional washing machine without apparent degradation.
The research team, led by Ramses Martinez, an Assistant Professor leading the Flexilab at Purdue’s Weldon School of Biomedical Engineering, has published their findings in Advanced Functional Materials.
‘We render textiles omniphobic – repellent to oils, water and dust – using fluorinated molecules that do not change the mechanical properties or ‘touch’ of the textile.’ Martinez explains to Nanowerk. ‘By combining embroidery with the spray-based deposition of fluoroalkylated organosilanes and highly networked nanoflakes, we create omniphobic triboelectric nanogenerators that can be incorporated into any fibre-based textile and be used to power wearable devices using energy harvested from human motion.’
Triboelectric nanogenerators (TENGs) are capable of harvesting electrostatic energy from a variety of human body motions in order to power wearable electronic devices. The omniphobic nanogenerators fabricated by the Purdue team are breathable, flexible and resistant to bending, stretching and washing, making them ideal candidates to power e-textiles and to serve as human-machine interfaces for the wearer.
They also designed their nanogenerators with large-scale fabrication runs in mind, using embroidery as a technique compatible with conventional textile manufacturing techniques.
‘Thanks to this invention, textile companies can embed flexible circuits in the clothes they manufacture and avoid including heavy rigid batteries to power them, making the textiles compatible with standard machine washing.’ Martinez points out. ‘Our nanogenerators are thin, flexible, breathable, inexpensive to fabricate (less than $0.04cm) and capable of producing a high power density. E-textiles based on nanogenerators repel water, stains and bacterial growth and show excellent stability under mechanical deformations and remarkable washing durability under standard machine-washing tests.’
To fabricate and integrate the RF-TENGS into textiles, the researchers used commercially available cotton, spandex and wool fabrics. These were spray-coated with conductive silver nanoflakes, a layer of polytetrafluoroethylene (PTFE) to encapsulate this electrode and silanizing agents (fluoroalkylated organosilanes) in order to make them oliophobic and conductive. They then embroidered designs on top of this bottom electrode layer with conductive sewing thread to integrate the RF-TENGS into the textile, securing the embedded electronics. In a final step, the embroidered designs were also rendered omniphobic by spray-coating them as well.
The RF-TENGS operate in vertical contact – separation mode, generating energy when the motion of the wearer induces the compression, bending or rubbing of the device. The repetitive separation and recontact of the textile layer of the top electrode and the PTFE coating of the bottom electrode generates charges on their surfaces due to the triboelectric effect.
Tapping – i.e. applying pressure to – the nanogenerator embroidery generates an electric charge that can be stored in a capacitor.
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