Reusable photonic wordpad with water as ink prepared by radical polymerization

Abstract

In this article, we report and demonstrate a novel photonic wordpad that is fabricated through the fast magnetically induced self-assembly of carbon-encapsulated superparamagnetic colloidals, followed by an instant radical polymerization to fix the photonic crystal structures inside a polyacrylamide glycol gel matrix. The photonic wordpad strongly diffracts blue light due to the colloids forming ordered chain-like structures in the solidified polymer matrix with uniform interparticle spacing under the induction of an external magnetic field. Distilled water is used as ink to write letters or Chinese characters with a different color on the wordpad because it can swell the polymer matrix and then increase the interparticle spacing within the chains, and as a result a red-shift in optical diffraction occurs. The photonic wordpad not only has an excellent reusability because the ink mark can be written or erased by introducing or removing the water in the surface layer of the photonic wordpad, but also is environmentally friendly and low-carbon owing to the reusability of the wordpad and non-toxicity of the ink. In addition, due to the use of the recent development of magnetically tunable assembly techniques, the processing time of this photonic wordpad is greatly reduced compared to using conventional assembly methods, which has an important significance in the large-scale industrial production in the future.