Drs. Rowan, Burnworth,  Tang, Kumpfer (all of Case Western),  Fiore, Weder (these last two from the University of Fribourg), Duncan, and Beyer (of the Army Natick Research Center) have reported (Nature) their development of a new polymer coating that can be repaired or healed via treatment with ultraviolet light.  Some plastics have been developed that can reshape themselves via reheating, which is time intensive.  This repair takes 30 seconds to complete!

This metallized rubbery (a metallo-supramolecular) polymer  is different.  Most polymers are comprised of long-chained repeating subunits.  This material uses metal ions (zinc, in the reported instance) to bind together thousands of small molecules.   As telechelic oligomers (a building block to make a polymer; which we generically call plastics), each end of the sub-unit is capable of forming the polymer.

When the polymer is exposed to a specified wavelength of ultraviolet light (UV), the polymer assumes a “molten”-like state (the metal bonds “relax”, reverts to smaller lengths, and exhibist a change in viscosity), whereby gaps and scratches are repaired.  After the exposure is removed, the material resolidifies.

As the mechanical properties were increased (strength, flexibility) by increasing polymeric bonds, its ability to heal decreased.  During their three years of research, the researchers, therefore, chose a moderate strength material with optimal mechanical capabilities and the ability to repair itself under UV irradiation.

To examine if they were successful in rendering the material healable,  small razor blade cuts were made at varying depths to the material.  When the material was  exposed to UV irradiation for 30 seconds, the cuts disappeared.  Moreover, the researchers examined the polymer’s toughness – and found the repaired material of the same mechanical properties as when it was first produced.   This was repeatable over several cycles of injury and repair.

It should be noted that the determining the proper intensity and wavelength of light was somewhat a trial and error effort.  Too much irradiation would render the polymer permanently damaged and too little provided no healing affect.  Also, the depth of the cut sets whether the coating fully heals.

So, imagine this coating on your car’s bumper (instead of the dinged up mess you probably have now).   After a month of parking at the local mall or the streets of your city, you could just flash a UV wand over the bumper- and, voila– your bumper would look brand new!  That’s technology at work!

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