Showing coloration of the same part of a membrane with different patterns (credit: Jing Wei)There is still a need for the old-fashioned writing materials of paper and ink, despite the digital juggernaut that has radically changed most of our communication. However, most of these traditional materials still end up being recycled or in landfills. To help lessen the waste involved, researchers have now developed rewritable media based on robust and fast-response photochromic systems in a cheap and environmentally friendly approach to producing printed materials with rewritable paper.
The material, which can be 'printed' on with a stencil and ultraviolet light, and also erased when exposed to oxygen in air or ozone, can be re-used several times before it needs to be recycled, significantly reducing the amount of paper that is wasted. While previous attempts at producing this kind of reusable paper have relied on photo-switchable organic molecules, such as viologens and leoco dyes, these molecules are toxic, expensive and undergo photodegradation, undermining their practical benefits.
As reported in the journal ACS Applied Materials & Interfaces [Wei et al. ACS Appl. Mater. Interfaces (2016) DOI: 10.1021/acsami.6b10620], this new study has produced a hybrid film by mixing low-toxicity tungsten oxide (WO3), an ideal photochromic material, with the common polymer polyvinyl pyrrolidone. To ‘print’ on the film, the team exposed the material to ultraviolet light, which changed its color from white to a deep blue.
“Compared with… known rewritable systems, the tungsten/polymer hybrid membranes are cheap, environmental benign and easy for large-scale preparation using electrospinning”Ting Wang
Showing coloration of the same part of a membrane with different patterns (credit: Jing Wei)To print pictures or words, stencils were utilized to ensure only the exposed parts turned blue. To erase the marks, the material can then be positioned in ambient conditions for a day or two, although heating worked to help the color disappear in only 30 minutes. Adding a small amount of polyacrylonitrile to the material also made the printed designs last up to 10 days. When the process was tested, it was found the material could be printed on and erased 40 times before any noticeable reduction in quality.
These hybrid membranes could be used multiple times in temporary displays, such as advertisements and posters – rather than only being used once and then having to be thrown out. As researcher Ting Wang emphasizes, “Compared with… known rewritable systems, the tungsten/polymer hybrid membranes are cheap, environmental benign and easy for large-scale preparation using electrospinning”. The next step for the research team is to look to improve the properties of the hybrid membrane, such as increasing its robustness, perhaps using a more robust polymer, and refining the coloration efficiency.