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Transformers: Materials that can change properties

Published online 25 September 2016

Multifunctional polymers exhibit different physical characteristics in response to varying stimuli.

Hebah Salama

Viologens are double-positively-charged molecules that respond to external stimuli such as chemicals or electric currents. 

In a new study, scientists from New York University Abu Dhabi demonstrate that when subjected to changing conditions, Viologen-based polymers change their behaviour and characteristics — giving them a wide range of potential uses, including “magic printing”, ammonia sensing, nuclear waste disposal and hazardous anionic toxins capture1

The variations are due to viologen’s redox-rich nature.

Generally, the nature and properties of any material determine the type of pollutants or substances they can interact with and therefore adsorb, remove or detect. 

The viologen-based polymers showed that they can be used for developing images upon exposure to sunlight, for instance, and therefore can be used as security inks in currency bills. They can also be used to capture and detect ammonia; changing their colour from yellow to green upon contact.

In their positively-charged state, they have the ability to remove negatively-charged toxins from water sources and so can be used for water purification. 

All polymers, in their different states, showed unprecedented iodine vapour adsorption, more effectively than any other previously reported material. Iodine vapour is a nuclear waste product. 

“These polymers are currently under investigation for dye removal from aqueous solutions, as well as for catalysis and gas separation,” says corresponding author Ali Trabolsi, professor of chemistry at New York University in Abu Dhabi.

The flexibility of these materials shows a potential for reusability, particularly in aspects that could serve the environment such as recycling and waste minimization. The idea is to “prepare a universal material where fabrication cost and residual wastes are reduced,” says Trabolsi. 


  1. Das, G. et al. Multifunctional redox-tuned viologen-based covalent organic polymers. J. Mater. Chem. A (2016).