The researchers of the Hokkaido University have developed a hydrogel that does the exact opposite of what polymer-based materials, such as plastic bottles, normally do. Usually these materials melt or lose hardness when exposed to heat.
The new hydrogel becomes 1.800 times more solid when exposed to heat: it could provide motorcyclists and motorists with accident protection.
This hydrogel hardens when heated and softens when cooled. The discovery of the team, published in the journal Advanced Materials, could lead to the manufacture of incredible protective clothing for road and sports accidents.
Takayuki Nonoyama e Jian Ping Gong of the University of Hokkaido and their colleagues were inspired by how proteins remain stable within organisms that survive in environments with extreme temperatures.
Organisms that even survive the heat of thermal springs and volcanic outbursts in deep waters remain alive thanks to enhanced electrostatic interactions such as ionic bonds. The team developed an inexpensive and non-toxic polyacrylic gel based on this principle.
Hydrogel that becomes indestructible to heat
A gel composed of acrylic acid (PAAc) was immersed in an aqueous solution of calcium acetate. PAAc alone acts like any other polymer-based material and softens when heated. But when calcium acetate is added, the outer residues of PAAc interact with the calcium acetate molecules, in a similar way to what happens inside thermophilic proteins, causing PAAc to act very differently.
The team found that when it reaches a critical temperature, in this case around 60 ° C, the material quickly transforms from a soft and transparent hydrogel into a rigid and opaque plastic.
The material becomes 1.800 times stiffer, 80 times stronger and 20 times harder than the original hydrogel when heated. The transition from soft to rigid is completely reversible as the temperature changes.
In addition, the scientists were able to fine-tune the switching temperature by adjusting the concentration of the ingredients.
They therefore demonstrated a possible application of the material by combining it with a glass wool fabric. So even this fabric, soft at room temperature, if rubbed against an asphalt surface for five seconds at a speed of 80 km / hour, hardens and does not suffer any damage, except for a few slight abrasions on the surface.
Takayuki Nonoyama states that “Garments made of similar fabrics could be used to protect against traffic accidents or sports injuries. Our material could also be used as a window covering, which would absorb heat to keep indoor environments cooler ”.
The gel polymeric it can be easily produced with versatile, cheap and non-toxic raw materials commonly found in daily life.