13 October 2010
As interest grows in clothes that do more than just keep you warm and preserve your modesty, Canadian scientists are developing non-woven textiles that exhibit a reversible colour change due to resistive heating.
Traditional fabrics can be improved by giving them another function useful for fashion medical or military applications, explains Alexis Laforgue at the National Research Council Canada Industrial Materials Institute, Boucherville.
Substances that change colour when an external stimulus is applied, such as heat) or electricity (know as (thermochromism or electrochromism respectively), can be added to fabrics to give them extra functionality. Laforgue's new non-woven material is simpler than many of its thermochromic and electrochromic counterparts because the fibres don't need to be woven through a fabric and the system doesn't need an electrolyte layer.
Applying a current causes the material to change colour
Laforgue prepared the material using templates made by electrospinning a mixture of an oxidising agent and a carrier polymer. A syringe containing the mixture is positioned about 15 cm away from a metal substrate. When a voltage is applied, the mixture is attracted towards it causing it to stretch into thin fibres that form a mat. Exposing the mat to monomer vapours, causes them to polymerise on contact. The template is them removed , leaving the polymer coating that shrinks inwards to form a non-woven mat of quasi-pure PEDOT (conducting polymer) nanofibers.
The reversible colour change is provided by a commercially available thermochromic ink painted or sprayed onto the conducting mats. When electrical currents below 100 mA are applied to the mats, they conduct well. Above the 100 mA threshold significant resistive heating occurs, triggering the ink's colour change.
Roger Mortimer, an expert in electrochromism and conducting polymers at Loughborough University in the UK points out that '100 mA is a relatively high driving current for clothing applications. This will need to be addressed in the future for the technology to become practical.'
Laforgue is continuing to develop the technology, and is now working on patterns composed of several inks with different colour-change temperatures, where different parts will be visible depending on the amount of current (and therefore heat) applied.