Soft, But Stronger Than Steel

By combining soft hydrogels with a woven glass fiber fabric, researchers have made a highly flexible composite material that is tougher than steel.

AsianScientist (Feb. 28, 2017) – Though 40 percent made of water, these hydrogels are tougher than metal. The study documenting these results has been published in Advanced Functional Materials.

Hydrogels are biocompatible materials that could be used in soft robotics and other applications. However, existing hydrogels are neither reliable nor strong enough for long-term use.

To address the problem, a team of researchers from Hokkaido University combined hydrogels containing high levels of water with glass fiber fabric to create bendable, yet tough materials, employing the same method used to produce reinforced plastics.

Using polyampholyte gels that they previously developed, the team created a composite material using fabric made from a single glass fibre of about 10μm in diameter. The resulting strong and stretchable material is made by simply immersing the glass fabric in a polyampholyte precursor solution.

When used alone, the fiber-reinforced hydrogels are 25 times tougher than glass fiber fabric, and 100 times tougher than hydrogels, in terms of the energy required to destroy them.

Scanning Electron Microscopy (SEM) images of the fiber-reinforced hydrogels. The polymer matrix (arrows) filled the interstitial space in the fiber bundles and connected the neighboring fibers. Credit: Advanced Functional Materials.

The team theorizes that toughness is increased by dynamic ionic bonds between the fiber and hydrogels, and within the hydrogels, as the fiber’s toughness increases in relation to that of the hydrogels. Consequently, the newly developed hydrogels are five times tougher compared to carbon steel.

“The fiber-reinforced hydrogels, with a 40 percent water level, are environmentally friendly,” said team leader Dr. Gong Jian Ping, “The material has multiple potential applications because of its reliability, durability and flexibility. For example, in addition to fashion and manufacturing uses, it could be used as artificial ligaments and tendons, which are subject to strong load-bearing tensions.”

The principles to create the toughness of the present study can also be applied to other soft components, such as rubber.

The article can be found at: Huang et al. (2017) Energy-Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft Composites.


Source: Hokkaido University.
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