Robots could get muscles using a new ferroelectric material

The team has demonstrated the potential of a new type of ferroelectric polymer that can convert electrical energy into a mechanical strain with greater efficiency than previous methods.

This material could be extremely useful in the development of medical devices, advanced robotics and precision positioning systems.

This new polymer could overcome the limitations of traditional piezoelectric polymer composites. In doing so, it would offer a promising avenue for the development of soft actuators, which are materials that change shape when an external force is applied to them.

In contrast to rigid actuators, soft actuators are extremely useful in the field of robotics due to its strength, power and flexibility. 

“Potentially we can now have a type of soft robotics that we refer to as 'artificial muscle',” said Qing Wang, Penn State professor of materials science and engineering and co-corresponding author of the study. “This would enable us to have soft matter that can carry a high load in addition to a large strain. So that material would then be more of a mimic of human muscle, one that is close to human muscle.” 

However, before "artificial muscles" can become a reality, these materials have to overcome a few obstacles. 

The first of them is the need to improve the force of soft materials. At the moment, soft actuation materials that are polymers have the largest strain, but they generate much less force compared to piezoelectric ceramics. This force is very important in the conversion of electrical energy to mechanical energy.

The second challenge is that a ferroelectric polymer actuator typically needs a very high driving field, which is a force that imposes a change in the system, such as the shape change in an actuator. In this case, the high driving field is necessary to generate the shape change in the polymer required for the ferroelectric reaction needed to become an actuator.  

The solution proposed to improve the performance of ferroelectric polymers was developing a percolative ferroelectric polymer nanocomposite – a kind of microscopic sticker attached to the polymer.

By incorporating nanoparticles into a type of polymer, polyvinylidene fluoride, the researchers created an interconnected network of poles within the polymer.  

This network enabled a ferroelectric phase transition to be induced at much lower electric fields than would normally be required. This was achieved via an electro-thermal method using Joule heating, which occurs when the electric current passes through a conductor and produces heat.

Using the Joule heating to induce the phase transition in the nanocomposite polymer resulted in only requiring less than 10 per cent of the strength of an electric field typically needed for ferroelectric phase change. 

“Typically, this strain and force in ferroelectric materials are correlated with each other, in an inverse relationship,” Wang said. “Now we can integrate them together into one material, and we developed a new approach to drive it using the Joule heating.

"Since the driving field is going to be much lower, less than 10 per cent, this is why this new material can be used for many applications that require a low driving field to be effective, such as medical devices, optical devices and soft robotics.” 

The study was recently published in the journal Nature Materials.