A Fishing Line That Changes Color Before Breaking

By Roland Piquepaille

If you enjoy fishing, I have some good news for you. According to New Scientist in "Light-emitting line reels in the big fish," American chemists have designed a blend of polymers which changes color if it has been exposed to a previous excessive stress. Before going to fight with a 300-pound marlin, you'll have to put your fishing line under ultraviolet light. If some parts of the line appear green, it should break soon, so it's time to switch to a new one before jumping in your boat. But these new fishing lines will not be on sale for a while. First, the changes of colors should be visible under normal light conditions, not only under UV. And real fishing lines are much stronger than the ones fabricated today in the lab. Read more...

Here is the somewhat 'teasing' introduction from the New Scientist article.

The big ones might not get away quite so often if an experimental fishing line finds its way to market. The new line changes colour when it has been subjected to too much stress, warning the angler that it is in danger of breaking.

Nylon fishing line is designed to have some stretch. But pull on it too hard -- when fighting a large fish, for example, or trying to get loose from a snag -- and it can reach the point of "non-recoverable deformation" at which it becomes seriously weakened.

So how did the chemists solve this problem?

The new line has been developed by Christoph Weder, Brent Crenshaw and Jill Kunzelman at Case Western Reserve University in Cleveland, Ohio, US. It contains a type of polymer called a phenylene vinylene oligomer, which fluoresces under ultraviolet light. Crucially, the colour of the light it gives off changes depending on the mechanical stress the molecule has been subjected to.

To make the fishing line, a small amount of the polymer is mixed into standard low-density polyethylene, making up 0.2% of the blend. When the line is not under stress, the polymer molecules are close together and emit reddish-brown visible light when illuminated by UV radiation. But when the material stretches and the polymer molecules pull apart, they fluoresce green. So an angler who feared that a section of line had been under excessive stress could examine it under UV light, and discard it if it glowed green.

	Here is a magnified knot of a laboratory sample of the fishing line. Under illumination with UV light, green (as opposed to orange) photoluminescence identifies regions that have suffered excessive deformation and may not survive the next big catch. (Credit: Brent Crenshaw, Case Western Reserve University).
	And here the line is "tied to an Adams Irresistible dry fly" (Credit: Brent Crenshaw, Case Western Reserve University). Here are links to larger versions of the above picture and of the adjacent one.

As I said above, there are still some hurdles to overcome before you could buy these fishing lines at your local fishing store.

Even more useful would be a polymer whose colour change is visible in normal light, says Crenshaw, who is a graduate student at Case Western's Functional Polymer Laboratory. He says the team is evaluating possible materials.

The polyethylene fishing line is for demonstration only: it would not be strong enough to stand up to even a 4-kilogram bass, Crenshaw says. But there is no reason the same could not be done with standard nylon fishing line.

For more information, please check the Functional Polymers group site at Case Western Reserve University, and in particular this page about functional polymer blends, where the researchers describe their projects.

Rather than designing and synthesizing new, complex functional macromolecules, minor fractions of a "functional additive" are blended with an "inert matrix polymer" in order to create (often after rather specific processing protocols) a new material with a unique or unusual property matrix.

One key project is focused on the design, synthesis, processing, and characterization of polymer materials with integrated mechanical deformation sensors. Materials with self-assessing capabilities are being investigated, in which photoluminescence is employed as the general sensing principle. The approach is based on the incorporation of small amounts of fluorescent dyes into conventional polymers and relies on the formation of nanoscale aggregates of these sensor molecules in the polymer matrix.

The equilibrium phase behavior of these systems can be influenced via the dye's chemical structure and the material's composition. The kinetic aspects of aggregate formation can primarily be manipulated via the processing protocol. Therefore the supramolecular architecture of the targeted polymer/dye nanocomposites can be very well controlled. The approach further exploits that mechanical deformation of these materials leads to shear-induced mixing, which transforms the nanophase-separated systems into molecular mixtures.

As you can see, fishing is not really a major concern for these researchers.

Sources: Kurt Kleiner, New Scientist, February 12, 2005; and various pages at Case Western Reserve University

Related stories can be found in the following categories.

• Chemistry
  
• Materials
  
• Miscellaneous
  
• Sensors