Second skin

Blackanthem.com, LONDON, England, April 6, 2005

"We even have someone showing how this works by pouring red wine down his silk tie into a wine glass!" says Ian George as he demonstrates Dstl's liquid repellent coatings in a slightly more conventional manner.

Ian, a member of the Dstl technology transfer team has a piece of blotting paper that is readily soaking up water. Meanwhile, in the other hand, a seemingly identical piece of the same material is unable to do the job it was designed for - the water droplets simply form beads and run off the surface.

But this is no sleight-of-hand trick, apart from the moistness of the wet blotting paper there are no physical differences apparent between the two samples.

"It's always good to introduce people to the technology with a highly visual but effective demonstration," says Ian. "It allows them to immediately grasp the benefits of the process."

The display illustrates how an invisible barrier has been formed on the surface of the paper, without any change to its physical properties. But how is it done? Stephen Coulson, the man behind the technology explains: "We use plasma polymerization techniques that can be applied to practically any material - wood, metal, glass, textiles, plastics - to form a coating that is incredibly liquid repellent," he says. "Even items constructed from a number of different materials can be coated, which makes the technique so unique."

The plasma coating works on the nano-scale, permeating the surface of the material so that the coating actually covers the fibres, rather than forming a barrier 'sheet' over the top. This means that the material retains its original bulk properties - a textile will keep the same drape qualities and will not stiffen or irritate while a sheet of metal will retain its sheen and strength.

Plasma polymerization is a gaseous phase technique, conducted in specially constructed plasma chambers under a vacuum. Plasma is a partially or fully ionised gas or vapour and sits somewhere between a liquid and a gas. In the case of the polymerization, different monomers are fed in to the plasma process. The deposition parameters can be adjusted to retain specific groups of the monomer, giving rise to a chemically tailored surface. Conventional plasma processing would etch would strip layers from a solid, but in the case of the Dstl plasma, a thin polymer layer is added instead.

"There are a lot of companies using plasma chambers and several academics are working on advanced plasma chemistry, but no commercial outfits have yet combined the two," says Ian. "We have the expertise at Dstl to do just that."

Origins and initial applications

The idea for the plasma polymerization has been several years in development. Originally the result of a MOD-funded research project at Durham University, the Intellectual Property now resides in Dstl Porton Down. Stephen has worked on the project since the days in Durham and cites an operational requirement for its conception. "The MOD wanted to find a way of creating an impenetrable coat to its NBC suits, to stop agents such as mustard and other liquid threats entering," he explains. "They wanted something that not only adds an extra dimension of protection, but is also comfortable to the wearer. The plasma technology is the only way to provide a durable polymer coating to a fully constructed garment."

Conventional NBC suits are understandably bulky due to the materials needed to keep chemical agents at bay. The plasma coating can create equivalent protection and can be added to normal fabric, making it easier for the soldiers to perform their duties.

"The coating could, in the future, be added to full suits, rather than individual components," says Stephen. "At the moment, materials in general use are treated in sheet form. The plasma vapour merely needs to make contact with the material to coat it. This is a great step forward."

At present the plasma chambers are too small to accommodate a full NBC suit, but already the team is trialing with a US company that specialises in such facilities. "Only once the technology is scaled-up will we fully realise its military and commercial potential," says Stephen.

Open market?

In keeping with government policy Dstl has been actively working to transfer the technology to civil applications and plasma polymerization already looks set to make an impact on the private sector. According to both Ian and Stephen, the possibilities for technology transfer extend through a number of markets as diverse as sportswear, electronics, designer clothing and medical instruments.

Although it's currently not a case of 'you've got it, we'll coat it', there seems to be a buzz about the new technology and its benefits to the civil sector. Naturally, as with all MOD based IP, there are several limitations, but the proof of concept stage is continuing apace.

"We already have several parties interested in licensing the patents," explains Ian. "And we hope to set this up as a spin-out venture as and when it's appropriate."

Ian is the man responsible for the technology transfer and IP decisions within the plasma team. He explains some of the potential market applications:

•Textiles/Clothing

This is perhaps the most obvious application of plasma polymerisation, using the technology to coat fabrics and full garments. The plasma coating is durable and extremely liquid repellent; it's surface energy is one-third the value of PTFE or Teflon™ .Furthermore, it can be applied to almost any fibre type - and because the coating is exceedlingly thin, the breathability of the garment is unaffected.

Another key benefit is that complete garments can be coated, rendering seams, zips and fasteners liquid repellent. Dstl is working with leading sportswear companies and manufacturers of luxury fashion brands to develop a new generation of water repellent and stain-resistant clothing.

Spilling a drink down that expensive silk tie may not draw as many gasps from dinner guests in the future, but plasma coated garments will still be able to be washed as normal. "It eases the cleaning process because it is a barrier between the stain and the garment," says Stephen.

•Medical

There is a multitude of applications in the life sciences sector and already the team has been coating medical components using the small plasma chamber at Porton Down. "The coating is bio-compatible," says Stephen. "This means it can be used in a range of medical and healthcare applications. Because the coating reduces the attachment of bacteria and the adhesion of material such as mucus and blood it is ideally suited to coat things such as catheters, IV lines and critical care vents."

•Electronics

From mobile telephones, personal computers and cameras through to computer chips and circuit boards the raft of applications in the electronics sector looks vast. "The coating will add a layer of unbeatable water-repellence," says Stephen. "Even the nightmare scenario of spilling a sugary drink on your computer will suddenly carry less weight!"

 

Source - Defence Science and Technology Laboratory