Researchers at Hokkaido University have developed a hydrogel that hardens when heated and softens when cooled. The applications of this research could revolutionize protective clothing for traffic and sports accidents. Their study is published in the journal of Advanced Materials.
Under normal circumstances, heat will denature materials. However, researchers Takayuki Nonoyama and Jian Ping Gong were able to develop their material on the temperature resistant capabilities of organisms that are found near hot springs and deep-sea thermal vents. The proteins within these thermophiles remain stable with heat due to enhanced electrostatic interactions such as ionic bonds.
The researchers used this biological mechanism to design an inexpensive, non-toxic polyacrylic gel. A gel made up of polyelectrolyte poly (acrylic acid) (PAAc) was placed in a calcium acetate aqueous solution. PAAc on its own acts like any other polymer-based material and softens when heated. However, when calcium acetate is added, PAAc's side residues react with the calcium acetate molecules, in a process similar to thermophile proteins, causing PAAc to take on different properties. When compared to the original hydrogel, the heated material was 1,800 times stiffer, 80 times stronger, and 20 times tougher.