Colouring by polymer stress instead of pigments
Material stress is normally not good for polymer films in paints and varnishes, after all it can lead to damage and failure of the protective function. A Nature article now shows how it can also be used for colouring.
Anyone who wants to colour a transparent polymer adds pigments. This has always been the case in the coatings industry. The authors of a recent Nature article show that crazing can be used to create an alternative for colouring.
Crazing creates zones perpendicular to material stress that consist of interlocking cavities on the micrometre scale connected by oriented polymer microfibrils. Normally, both the voids and the fibrils have a wide size distribution, which results in the affected areas normally appearing white.
The researchers led by Masateru M. Ito from the University of Kyoto have now succeeded in influencing this size distribution in a targeted manner and in generating an alternating interference pattern in such a way that the desired colours can be produced in a targeted manner by scattering effects.
In order to create the structures, the researchers rely on selective light-sensitive polymer layers in which cross-links are formed selectively, separated by other layers in which no cross-linking takes place. This leads to the build-up of tensile stress across the non-crosslinked layers.
Only a few colours have yet been formed, but more are expected to be possible.
Source: Nature 570, 363-367 (2919)
