Glow in the dark garments
Battery-powered electroluminescent (EL) yarns are being developed at The University of Manchester, UK, to create clothing that glows in the dark, allowing the wearer to be visible in all lighting conditions, improving personal safety.
The material consists of an inner conductive core made from a silver coated nylon (polyamide) yarn covered with commercially available EL ink, a transparent conductive polymeric layer that encapsulates the ink, and then an outer conductive fibre. The team at The William Lee Innovation Centre in Manchester (WLIC), where the textile is being developed, is unable to reveal the exact composition.
‘Micro-encapsulated EL particles and other polymeric layers are deposited on the surface of a conductive core yarn using a precise micro-dispenser system and cured using UV,’ explains Dr Tilak Dias, Head of WLIC. ‘The EL particles are held between two conductive surfaces, and we create a high frequency electric field [using an inverter] to excite the particles.’ Light is emitted at the contact points between the inner and outer yarns.
‘The method of constructing [a garment] is to knit a pre-determined area of the base knitted structure from EL yarn, using a technique called Intarsia, on a modern computerised flat bed knitting machine,’ says Dias. ‘The same technique is used to create conductive pathways to energise the EL area. As such, the power source is not embedded into the knitted structure.’ The team believes conventional weaving technology also be used.
The research aims to improve high visibility (HV) clothing used by the emergency services, cyclists and highway maintenance workers. The UK’s Health and Safety Executive stipulates that HV clothing should distinguish the wearer from an ambient background, using colours such as fluorescent yellow and retroreflective material to make the wearer visible to oncoming vehicles in poor lighting conditions.
But the team at WLIC argues that such materials can be ineffective as they depend on external light sources (such as headlights) to make them visible, which is problematic in low light situations. Moreover, the driver of a vehicle might not see the wearer until it is too late.
Researchers are optimising the new material for flexibility, washability and brightness. Initial results suggest that the power of luminescence depends on the EL fibre density in the knitted or woven structure, and that light emitted from a single strand of EL yarn is greater than that of photoluminescent glow yarns used in HV products. Potential applications also include flexible woven or knitted road safety signs that communicate written instructions.
Paul LeGood, Technology Translator for SMART.mat, the smart materials, surfaces and structures node of the Materials KTN, says, ‘The fact that the light does not emit heat makes it possible to be worn as a normal garment. Electroluminescent light has been used in the interior of ladies’ handbags so that the darkest depths can be seen without melting cosmetics or confectionary'.
‘Phillips Electronics has carried out extensive research on glow in the dark materials. Their technology, Lumalive, integrates flexible sheets of light emitting diodes into the fabric. Although still under development, novelty items such as Halloween constumes can be purchased.’
Yarns that incorporate basic electronic units, such as the transistor, without being ‘electronic bricks around the body’ are also being developed at WLIC. These fibres are claimed to be fully washable and can be manufactured using existing techniques. Potential applications include non-invasive sensing and imaging systems for healthcare monitoring and smart wound care.