Just add water for new wonder material

June 25, 2015

Just add water for new wonder material

Walking on water and a liquid that can stop a bullet sound like the powers of comic book superheroes.

Yet a fluid that hardens on sudden impact is helping researchers develop ground-breaking new solutions for protecting life and solving safety issues with batteries in electric cars.

Dr Tongfei Tian, an Associate Research Fellow at UOW’s Faculty of Engineering and Information Sciences, has been working on shear thickening fluids (STFs) under the guidance of Professor Weihua Li. STFs are a mixture of particles and liquid that suddenly harden within milliseconds of impact and return to liquid state once the force is removed.

The fluids have been investigated for use as liquid body armour by mixing it with the protective synthetic fibre Kevlar. The combination of thickening fluid and Kevlar has been shown to stop a bullet with greater effect than Kevlar alone, while STFs’ liquid state allows the wearer a greater range of movement and comfort.

SHear thickening fluids - how it works
An STF is a mixture of a liquid and particles, such as silica. In liquid form, the weak molecular interactions between the particles permit them to move around freely in the liquid without binding to one another. A hard impact to the fluid forces the particles to temporarily assemble into hydroclusters – long irregularly shaped chains of molecules. This is because the energy of impact is much greater than the energy between the particles. The hydroclusters overlap to form a mesh-like structure, which dramatically increases the viscosity, or thickness, of the liquid. As soon as the energy from the mechanical stressor disappears, this process reverses itself, and the substance returns to a liquid state. Source: Dartmouth Undergraduate Journal of Science (read online).

SHear thickening fluids - how it works

An STF is a mixture of a liquid and particles, such as silica.

In liquid form, the weak molecular interactions between the particles permit them to move around freely in the liquid without binding to one another.

A hard impact to the fluid forces the particles to temporarily assemble into hydroclusters – long irregularly shaped chains of molecules. This is because the energy of impact is much greater than the energy between the particles.

The hydroclusters overlap to form a mesh-like structure, which dramatically increases the viscosity, or thickness, of the liquid.

As soon as the energy from the mechanical stressor disappears, this process reverses itself, and the substance returns to a liquid state.

Source: Dartmouth Undergraduate Journal of Science (read online).

The advantage of these fluids is that they can harden and then return to a liquid state, whereas rubbers, gels or other soft materials can’t be altered.

Recently, the UOW team successfully combined STFs with other thickening materials, such as those that harden in response to magnetic force, to create multifunctional smart fluids that have promising applications in battery technology.

“Lithium ion batteries are used widely in consumer electronics and are being developed for electric vehicles,” Dr Tian said. “But there are issues with safety and reliability, especially with the large battery packs needed for electric cars.

"Most of the current research has been focused on reinforcing the battery packaging and preventing it from puncturing during a crash.

"We’ve shown that our smart thickening fluids could be used in the battery. They harden on impact and resist crushing to protect the battery as well as have higher conductivity than current electrolytes used in batteries.”

The good news is that unlike many other so-called wonder materials, such as graphene, STFs can be made cheaply from readily obtainable combinations of materials, such as simple mixture of cornstarch and water.

Dr Tian joined UOW in July 2008 and was drawn to research on STFs after watching a video on YouTube that showed people were able to walk on water after filling a pool with it.

“The video grabbed my attention and Professor Weihua Li, who is the leading scientist in this area, accepted my application to be a research student,” he said.

He is now doing postdoctoral research for an ARC Discovery Project under the supervision of Professor Li. The final hurdle the UOW research group is working on is the STFs’ achilles heel: they absorb moisture, which diminishes and eventually destroys its thickening capability.

His work has also led to a scholarship award from the Chinese Government for Outstanding Self-Financed Students Studying Abroad. His supervisor, Professor Li, also received an outstanding supervision award. The highly competitive awards are provided to support outstanding self-financed students studying outside of China.

Professor Li, who is Director of the Advanced Manufacturing Technologies Research Strength, said the award was a tribute to Dr Tian’s hard work during his PhD study and it reflected the strength of the students within the School of Mechanical, Mechatronics and Materials Engineering.

“This is a tremendous success for Tongfei and a high recognition of his PhD work in the field of smart materials and structures”, Professor Li said. Dr Tian was one of three UOW recipients who each receive a cash prize.

The other winners were: Dr Guanglin Xia (Institute for Superconducting and Electronic Materials, supervised by Professor Zaiping Guo and Professor Hua Kun Liu) and Dr Yubing Shi (Australian National Centre for Ocean Resources and Security, supervised by Professor Robin Warner and Professor Warwick Gullett).

Dr Tian will in October this year take up an assistant professorship with Tohoku University, Japan, which is ranked in 70th worldwide in the Times Higher Education Subject Ranking 2014-15: Engineering & Technology.