Hokkaido University scientists have created a hydrogel that does the opposite of what polymer-based supplies, like plastic bottles, usually do: their material hardens when heated and softens when cooled. Their conclusions, published in the journal Advanced Materials, may lead to the fabrication of protective clothes items for traffic and sports-associated accidents.
Jian Ping Gong and Takayuki Nonoyama of Hokkaido University and their colleagues have been inspired by how proteins stay stable inside organisms that survive within excessive-heat environments, like hot springs and deep-sea thermal vents. Usually, heat “denatures” proteins, altering their structure and breaking their bonds. But the proteins within thermophiles stay stable with heat attributable to enhanced electrostatic interactions such as ionic bonds.
The staff developed an inexpensive, non-poisonous polyacrylic gel-based mostly on this idea. A gel composed of polyelectrolyte polyacrylic acid (PAAc) was immersed in a calcium acetate aqueous solution. PAAc on its acts like any other polymer-based materials and softens when heated. However, when calcium acetate is added, PAAc’s aspect residues interact with the calcium acetate molecules, in a way just like what occurs inside thermophile proteins, causing PAAc to behave very differently.
The group found that their formerly smooth gel separates into a polymer dense “phase” and a sparse polymer one as the temperature rises. When it reaches a critical temperature, in this case, around 60°C, the dense part undergoes dehydration, which strengthens ionic bonds and hydrophobic encounters between polymer molecules. This causes the material to quickly transform from a soft, transparent hydrogel to an inflexible, opaque plastic.
The heated material was 1,800 times stiffer, 80 times more durable, and 20 tougher than the original hydrogel. The soft-to-rigid switching was utterly reversible by alternately heating and cooling the fabric. Moreover, scientists could high quality-tune the switching temperature by adjusting the concentration of the elements.