This unique polythene extrusion has some remarkable characteristics and may be used as a single-lesson introduction to smart materials. Below 27°C the cord is pink but above this temperature the colour disappears. The pink then reappears when the temperature drops below 27°C.
The cord also exhibits highly unusual behaviour if stretched. When pulled steadily it suddenly necks down at random to a second smaller diameter – and gets stronger! Eventually the whole length of the material reduces to the second diameter as the long molecules are forced to align along the axis of the cord. As the cord stretches there is a temporary loss of colour; the mechanical effort of stretching the cord causes heating – thus neatly demonstrating energy transfer.
Short lengths of smart cord may be made into wristbands. At very low cost these could be worn as a constant reminder of the material’s unique properties and taken off for use in homework investigations.
Sold by the metre. Cord diameter approximately 1.5mm.