Can you fold your phone at will? Elastic ferroelectric material developed by scientists can do it!

Produced by: Science Popularization China

Author: Shi Wuyao (PhD in Biology)

Producer: China Science Expo

Can you imagine wearing a piece of close-fitting clothing that can monitor your heart rate, breathing and other information at any time, allowing you to always pay attention to your health? Can you imagine that the mobile phone you use every day can be soft, close to the body and foldable at will?

The advent of new elastic ferroelectric materials may make these ideas a reality.

On August 4, 2023, the Flexible Magnetoelectric Functional Materials and Devices Team of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, published an article in the journal Science on a new type of polymer ferroelectric material. This material has both elasticity and ferroelectricity, filling a major gap in the field of materials.

The research results were published in the journal Science

(Image source: Science magazine)

What are ferroelectric materials?

Ferroelectric materials are an important class of insulating functional materials in the field of materials, usually referring to materials with ferroelectric properties, mainly crystalline materials .

In some crystalline materials, the internal positive and negative charge centers of the basic unit cells that make up the crystal do not coincide, so an electric dipole moment is generated, resulting in spontaneous polarization of the crystal, which in turn gives the material ferroelectric properties.

Diamond, one of the hardest crystalline materials

(Photo source: veer photo gallery)

Since the direction of the electric dipole moment of the crystal changes with the change of the external electric field, ferroelectric materials have their own memory function and can freely store and read data.

Ferroelectric materials are mainly used in important fields such as electrical sensors, optoelectronic devices, high-precision motors, etc., and are also an indispensable part of the electronic products we use in our daily lives.

Since the crystal itself has no elastic properties, when it is subjected to external force, the rebound force it generates is less than 5%, so traditional ferroelectric materials also have no elasticity .

With the development of flexible electronics, intelligent sensing, wearable electronic devices, etc., people have put forward higher requirements on the performance of ferroelectric materials.

Ferroelectric materials are not only needed to achieve data storage and retrieval, sensing and other performance improvements, but they also need to have elasticity to achieve material deformation, and then achieve arbitrary bending of the material to fully meet wearable needs.

Wearable devices: Smart watches

(Photo source: veer photo gallery)

How to make ferroelectric materials "bounce"?

The crystalline region inside the ferroelectric material is the main area where it performs its functions.

The arrangement of molecules in the crystallization regions of traditional materials is a linear and regular structure, and there is no covalent connection between the molecular chains. Therefore, when external force is applied to the material, the internal structure of the material will be destroyed, thereby causing the destruction of the ferroelectric properties of the material.

Scientists used polyvinylidene fluoride-trifluoroethylene as the reaction matrix material, selected chain-shaped polyethylene oxide diamine with bendable and foldable structure as the cross-linking agent, and adopted the "micro-cross-linking method" to wrap the crystals in the network formed by the cross-linking agent, thus completing the preparation of the material.

Concept and synthesis of elastic ferroelectric materials

(A) Schematic diagram of the change in molecular size of ferroelectric materials under external force and the stress-strain curve of plastic and elastic deformation; (B) Schematic diagram of elastic polymer cross-linking

(Image source: Reference [1])

The new material has an interwoven fishing net-like structure inside. When it is subjected to an external force of 70% strain, the fishing net-like structure can disperse the external force and ensure that the molecules in the crystallization area function normally, thereby maintaining the ferroelectric properties of the material .

At the same time, by controlling the use of cross-linking agents during the material synthesis process, it can be ensured that the material can produce reversible deformation . The elongation rate of the new material can reach 125%, which is dozens of times that of traditional materials.

Not only that, after enduring thousands of repeated stretching, the elastic ferroelectric material can still maintain a stable shape, which shows its long service life.

The advent of this elastic ferroelectric material has made it possible for people to wear elastic vests that monitor heart rate in real time and hold soft and close-fitting mobile phones.

Elastic response of materials under strain

(AC) Deformation of the material under 0 and 70% strain; (D) Changes in the electric field and polarization intensity of the material under 0 and 70% strain; (E) Elastic response of the material under different strains

(Image source: Reference [1])

What other smart materials are there?

Materials are needed in every aspect of our lives, from the clothes we wear to the buildings we live in. So, in addition to elastic ferroelectric materials, what other smart materials have scientists developed?

This requires me to first introduce to you some self-healing polymer materials .

Scientists used bioengineering to transform Escherichia coli so that it could sense external blue light and achieve the expression of certain functional proteins through the regulation of external blue light.

Subsequently, scientists further mineralized the biofilm of E. coli and finally obtained a mineral composite material . This material has good biocompatibility and can be used in the field of bone damage repair in the future, bringing good news to human health.

Bone damage repair

(Photo source: veer photo gallery)

The next thing I want to introduce to you is intelligent temperature-variable building materials.

Scientists have used knowledge of electrochemistry and optics to design an intelligent, automatic temperature-changing building material.

The material consists of solid copper, which retains infrared energy and raises its temperature, and an aqueous electrolyte solution, which emits infrared light and lowers its temperature.

Solid copper block

(Photo source: veer photo gallery)

Therefore, when the temperature around the material changes, the material can automatically change the emissivity of the surrounding infrared thermal radiation, thereby achieving automatic temperature regulation.

It can be seen that buildings constructed using this building material can automatically keep warm in winter and cool in summer.

Next comes the appearance of photoresponsive polymer materials.

With the advancement of science and technology, scientists have developed a light-sensitive liquid crystal polymer film containing photochromic azobenzene, and coated it on the surface of the robot to put on a coat for the robot.

By changing the external light, people can use the external light to control the robot's grasping and releasing behavior.

Visible light controlled manipulator constructed by using azodiphenylacetylene liquid crystal polymer material and polyethylene film

(Image source: Reference [5])

Technology changes life, and innovation makes life better. I believe that with these smart materials, transportation, medical health, construction engineering and other fields will achieve faster development.

References:

[1]Liang Gao et al. Intrinsically elastic polymer ferroelectric by precise slight cross-linking.Science381,540-544(2023).

[2] Xiao Jing, Sun Xiaoqin, Liu Hanxing, et al. Research progress of textured perovskite ferroelectric materials [J]. Bulletin of Silicate, 2004, 23(5):5.

[3]Wang Y, An B, Xue B, et al. Living materials fabricated via gradient mineralization of light-inducible biofilms. Nat Chem Biol 2021 Mar;17(3).

[4]Chenxi Sui, Jiankun Pu, Ting-Hsuan Chen, et al. Dynamic electrochromism for all-season radiative thermoregulation. Nat Sustain (2023).

[5]Cheng F., Yin, R., Zhang Y., Yen C.-C., Yu Y., Fully plastic microrobots which manipulate objects using only visible light. Soft Matter, 2010, 6, 3447.