Recently, Guo Jinbao, a professor at Beijing University of Chemical Technology, and his team have created a multifunctional liquid crystal elastomer with the characteristics of structural intrinsic luminescence, self-healing, and shape memory.
Figure | Guo Jinbao (Source: Guo Jinbao)
The network structure of this elastomer uses imigo-dynamic covalent bonds, which form aggregation and dissociation conformations in the material, giving the material a variety of functions.
This makes the elastomer show excellent characteristics in optical properties and mechanical properties, and provides new possibilities for the application of liquid crystal elastomers in many fields.
（来源：Advanced Materials）
In terms of application prospects, this material can realize the storage and transmission of information.
Compared with traditional information-recording materials that rely on light-responsive molecules, materials based on cluster luminescence do not require complex organic synthesis, thus avoiding environmental pollution and potential threats to human health.
At the same time, the written information has extremely high resolution and stability, which can efficiently realize the storage of information, and is further used in trademark anti-counterfeiting, laying the foundation for the application in the fields of display technology and display orientation.
In addition, the material can be made not only into films, but also into fibers, expanding its application potential in different forms.
Using its reprogramming capabilities during stretching and twisting, flexible robots with intelligent perception and adaptive morphology can be designed.
During tensioning and twisting, internal stresses are stored through a dynamic cross-linking network. When the ambient temperature changes, the reprogrammed fibers can convert the internal energy into regular motion, allowing for directional advancement. It can be seen that this material has great application potential in the field of soft intelligent robots.
At the same time, the material also has great application potential in the field of fluorescent textiles. For example, fibers can be custom woven and a variety of intricate patterns can be designed.
It is also known that the material is unique in that it has a self-healing function, which allows the fibers to self-repair in the event of a thread breakage without the need for additional sutures.
The repaired pattern retains its fluorescence and does not break when stretched. As a result, the material can not only be used for eco-friendly practical production, but also has a high degree of customizability that enhances user acceptance.
It is difficult to balance the "optics & mechanics" properties of liquid crystal elastomers
Based on the background of sustainable development in contemporary society, the development of functional integrated materials has also been put forward in many aspects, including environmental protection, resource sustainability, energy efficiency, etc.
Materials should have as low environmental impact as possible, reducing resource consumption and waste generation during production, use and disposal, as well as high-performance and socially responsible production processes to achieve a sustainable impact on the environment and society.
As a new class of smart materials, liquid crystal elastomers (LCEs) have become important contributors to sustainable development through the improvement of material synthesis technology and the expansion of multi-functionality.
It enables efficient use of resources, reduces waste and energy consumption, and can be used in areas such as smart materials and wearables to drive sustainable energy and lifestyles through precise control of structure and performance.
In addition, for some emerging technologies such as wearable technology, flexible electronic devices, smart materials, etc., materials with versatility and customizability are needed to realize potential applications.
Therefore, the study of LCE aims to address the limitations of existing materials in specific applications, while also exploring new structures and properties to meet growing technical and societal needs.
Among them, LCE materials with photonic properties exhibit tunable and flexible optical behavior, providing a revolutionary path for applications from soft actuators, information storage media, and optical sensors.
However, traditional methods are often accompanied by complex structural design and preparation processes. In addition, the balance and fusion of optical and mechanical properties has not been explored and remains a challenge. Based on this, Guo Jinbao's team carried out this study.
（来源：Advanced Materials）
Accidental discovery of fluorescent properties
According to reports, the research group initially planned to develop a new liquid crystal elastomer with dynamic imine bonds on the basis of previous research [1]. However, in the course of the research, it was unexpectedly discovered that the material has fluorescent properties.
Therefore, before starting to study the mechanical properties and dynamic covalent bond properties of liquid crystal elastomers, they tried to first conduct a detailed exploration of the fluorescence properties of liquid crystal elastomers, including spectral characterization and verification of cluster luminescence.
Using multi-peak analysis theoretical calculations and comparative experiments, the team further determined the contribution of imine and secondary amine to fluorescence luminescence wavelengths, which enabled the preparation of multi-fluorescent LCEs by controlling the content of different functional groups.
They also built a molecular library on this basis to design novel liquid crystal elastomers with cluster luminescence properties.
The mechanical properties of liquid crystal elastomers are of great significance for their practical applications, so they systematically studied the mechanical properties of the material and the dynamic network and physicochemical stability of the elastomers.
The first is the determination of the stress-strain curve, as this involves the evaluation of the soft elasticity of the material and further applications.
In addition, rheological experiments and thermal expansion experiments were carried out to confirm the dynamic network and physicochemical stability of the prepared elastomers.
How to put a new material into practical use is also a very important topic.
So, after fully understanding the performance of this LCE, they set out to solve the problem of how to combine the function of cluster luminescence with the excellent mechanical properties of liquid crystal elastomers.
With this goal in mind, they first proposed the potential for theoretical applications of multi-module display stitching of LCEs with different fluorescent colors. This design provides a versatile device for display and optoelectronic applications.
In the experiment, they found that the LCE cluster luminescence before and after polymerization is quite different, so according to this property, the research group can completely realize the information writing independent of the photosensitive substance, which greatly reduces the production cost of information recording materials.
（来源：Advanced Materials）
In addition, given the material's versatility, the team was exposed to work on soft intelligent robots and liquid crystal elastomer fibers, so they immediately set out to investigate.
They found that if it was just a single fiber at first, its movement was disorganized. Therefore, on this basis, a single fiber is twisted and bent to form a double-strand fiber, and a soft robot capable of directional motion is obtained.
Finally, returning to the most basic use of fibers, they found that the material could be used as a fluorescent fabric, and dynamic imine bonds could also give the fabric a self-healing function.
The fluorescence phenomenon was, in fact, an unexpected discovery in this study. In the past, in order to achieve luminescence, it was necessary to incorporate conventional fluorescent molecules containing large conjugated structures.
However, the team's material system doesn't contain this structure, so they were thrilled when they found out.
In other words, this material can not only achieve luminescence function, but also avoid a large amount of organic synthesis, which greatly saves resources.
However, at that time, they did not have enough understanding of cluster luminescence, so after a large number of literature reviews and experimental proofs, the research group finally figured out the mechanism of this non-traditional luminescence and extended it.
"In this way, we used an accidental discovery as an introduction, and revealed its inner mechanism in detail, and finally it can be truly applied to daily life, which is an evocative process." Guo Jinbao said.
最终，相关论文以《动态亚胺键实现簇触发自发光、快速自修复和自适应重编程液晶弹性体》（Cluster-Triggered Self-Luminescence, Rapid Self-Healing, and Adaptive Reprogramming Liquid Crystal Elastomers Enabled by Dynamic Imine Bond）为题发在 Advanced Materials[2]。
Qingyan Fan is the first author, and Guo Jinbao serves as the corresponding author.
Figure | Related papers (Source: Advanced Materials)
In the future, they will focus on improving the following aspects:
First, stability and durability are improved.
Enhance the stability and durability of cluster luminescent liquid crystal elastomers, extend their service life, and maintain stable performance under various environmental conditions.
Second, the improvement of the preparation process.
Optimize the preparation process, improve production efficiency, reduce costs, and achieve large-scale production to promote the commercial application of cluster luminescent liquid crystal elastomer technology.
Third, the expansion of application fields.
Explore the wider applications of cluster-emitting liquid crystal elastomers in virtual reality, augmented reality, wearables, flexible displays, and lighting, and drive their technology and market development.
At the same time, they plan to use machine learning techniques to screen and build molecular libraries to further reduce the cycle and cost of personalized material development.
It is hoped that the performance and application range of cluster luminescent liquid crystal elastomers can be continuously improved to meet the growing market demand and technical challenges, promote their wide application in electronic display, lighting and other fields, and promote the development and innovation of liquid crystal technology and luminescent materials.
Resources:
1.Adv. Funct. Mater.， 2022， 32，2107145; ACS Appl. Mater. Interfaces， 2022， 14， 53348; Cell Rep. Phys. Sci.， 2023， 4， 101583; Sci. China. Mater.， 2024， 67， 355; Sci. China. Chem.， 2024， DOI: 10.1007/s11426-024-2031-0; Light-Sci. Appl.， 2024， DOI: 10.1038/s41377-024-01479-1.
2.Fan, Q., Tang, Y., Sun, H., Guo, D., Ma, J., & Guo, J. (2024). Cluster‐Triggered Self‐Luminescence, Rapid Self‐Healing and Adaptive Reprogramming Liquid Crystal Elastomers Enabled by Dynamic Imine Bond. Advanced Materials, 2401315.
Operation/Typesetting: He Chenlong