Detailed in Nature Communications, the work is claimed to have the potential to make materials manufacturing more sustainable and environmentally friendly.
The process uses PNIPAM (poly(N-isopropylacrylamide)) ink. When this PNIPAM ink is extruded through a needle into a calcium chloride salt solution, it instantly solidifies as it contacts the salt water.
This rapid solidification is driven by the salting-out effect, where the salt ions draw water molecules out of the polymer solution due to their strong attraction to water. This removal of water causes the hydrophobic polymer chains in the PNIPAM ink to densely aggregate, creating a solid form.
In a statement, senior author Jinhye Bae said: “This is all done under ambient conditions, with no need for additional steps, specialised equipment, toxic chemicals, heat or pressure.”
Traditional methods for solidifying polymers typically require energy-intensive steps and harsh substances. In contrast, this new process harnesses the interaction between PNIPAM and salt water at room temperature to achieve the same result, but without the environmental cost.
The process is also reversible as the solid structures produced can be dissolved in fresh water, reverting to their liquid form. This allows the PNIPAM ink to be reused for further printing.
“This offers a simple and environmentally friendly approach to recycle polymer materials,” said Bae, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering.
To demonstrate the versatility of their method, the researchers printed structures out of PNIPAM inks containing other materials. These include an electrical circuit using an ink made of PNIPAM mixed with carbon nanotubes, which powered a light bulb. This printed circuit could also be dissolved in fresh water, showcasing the potential for creating water-soluble and recyclable electronic components.
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