Composites containing multiple elements have important application value in many fields, and controlling the distribution of each element in the material is crucial to the overall structure and properties of the material.
When developing bulk materials at a macroscopic scale, researchers can generally use phase diagrams to design material structures, element distributions, etc.
When the overall size of the material is reduced to the microscopic scale such as nanometer and sub-nanometer, the macroscopic phase diagram may no longer be applicable.
For example, theoretical studies have shown that the immiscible gap between the elements will gradually decrease or even be eliminated in nanoparticles with a size of 1-10 nanometers.
However, at the experimental level, there is no systematic and comprehensive experimental evidence in the field to answer how the size of nanomaterials affects the thermodynamic miscibility behavior between elements.
The lack of knowledge about the thermodynamic behavior of elements at the microscopic scale has hindered the design and construction of multivariate nanomaterials with specific structures.
In this context, Professor Chen Pengcheng and collaborators at Fudan University designed a binary model system from the perspective of seeing is believing, and explored how the miscibility of immiscible elements changes in nanoparticles of different compositions and sizes.
Figure | Chen Pengcheng (Source: Chen Pengcheng)
In this way, they systematically reveal the compatibility transition phenomenon of immiscible elements in microscopic materials, and explain the key factors that cause the compatibility transition of elements in combination with theoretical simulations.
The reviewers of related papers commented: "This work will change researchers' original understanding of the fragmentation of thermodynamic behavior at the nanoscale. Through high-quality experimental data, the authors systematically demonstrated the change process of elemental compatibility from macroscopic to microscopic for the first time, which is of great significance for the application of nanomaterials in many fields. ”
Chen Pengcheng said that this work shows that elements that are incompatible at the macro level may actually be compatible at the micro scale, which provides new ideas for the development of multivariate nanomaterials and greatly broadens the design space.
At present, multivariate nanomaterials have been widely used in high-efficiency catalysis, nano-optoelectronic devices and other fields. The findings of this work will provide a basic theoretical basis and guidance for scholars on how to better design the structure of multivariate nanomaterials.
Some materials that were previously considered to have application value but were neglected due to instability may not have stability problems, and these multivariate nanomaterials still have important research significance.
According to reports, a few years ago, when Chen Pengcheng's postdoctoral career had just begun, after many discussions with his supervisor, he decided to study the general direction of elemental compatibility changes in nanoparticles.
Since his previous work has focused on multivariate nanomaterials, he has some basic understanding of this direction. At the same time, after reading the relevant literature, there is also a preliminary assessment of the challenges that may be encountered.
It includes the search for model nanoparticle systems suitable for research, the preparation of nanoparticles with a wide range of parameters, the characterization of the thermodynamic distribution of different elements in the particles, and the mechanism interpretation of thermodynamic phase behavior.
After determining the general direction, Chen Pengcheng began to synthesize binary nanoparticles composed of immiscible elements. During this period, a number of systems were screened.
Since the object of this study is nanoparticles with ultra-small size and composed of incompatible elements, these two characteristics determine that these nanomaterials themselves are not easy to synthesize, and in terms of characterization, nanoparticles are also very susceptible to external environmental influences.
During the whole research process, this stage spent the most time, including optimizing the synthesis of model nanoparticles with different compositions and sizes, performing systematic electron microscopic characterization of nanoparticles, and analyzing the thermodynamic phase behavior and stability of nanoparticles.
The key experimental data were basically obtained in the early stage of this stage, but it took a lot of time to make the whole work more systematic and comprehensive, and after obtaining most of the experimental data to fully confirm the research conclusions, it took nearly a year to carry out in-depth exploration of the theoretical level of the elemental compatibility transition mechanism.
最终，相关论文以《不混溶元素在纳米尺度上完全混溶》（Complete miscibility ofimmiscible elements at the nanometre scale）为题发在 Nature Nanotechnology[1]，陈鹏程是第一作者，美国加州大学伯克利分校杨培东教授担任通讯作者。
图 | 相关论文（来源：Nature Nanotechnology）
How to interpret the contradictory views in the literature and the conflict points between them and this work is one of the difficulties encountered by Chen Pengcheng.
In the literature, many theoretical studies believe that the core-shell structure is the most stable configuration of the binary immiscible system, but this conclusion is actually in conflict with many experimental reports, including this work, and the difference between the results of theoretical research and experimental research has not been solved in the field.
After nearly a year of repeated endless loops of theoretical simulation-discussion-unexplainable, and then simulation-discussion-unexplainable, some key factors that are easy to ignore in theoretical research and unavoidable in experimental research are finally found.
Through a reasonable interpretation of the differences between the conclusions of the two research paradigms, it also promotes the understanding of the thermodynamic behavior of elements at the microscopic scale.
It is also reported that one of the major research difficulties of multivariate nanomaterials is their huge parameter space, including element combination, element ratio, material size, crystal structure, alloy phase, etc., which requires scholars to establish practical and effective high-throughput research methods.
On the one hand, from the perspective of experimentation, it is necessary to build a high-throughput experimental platform to accumulate corresponding key data sets, and on the other hand, from the perspective of theoretical research, AI will be a very good means of help.
Based on existing datasets, AI will help researchers accelerate the pace of material development. Therefore, like many other fields of experimental science, experimental research and AI research need to be deeply integrated to complement each other and promote each other.
It is also reported that in the team's previous research [2], a database-based preparation method for multivariate nanoparticles was pioneered. This method was selected as one of the top ten emerging technologies in the field of IUPAC chemistry in 2022, opening the door to systematic research on multivariate nanosystems, and has received extensive attention and follow-up from international peers.
At present, in the field of multivariate nanomaterials, there has been a lot of work focusing on how to prepare new materials for energy catalysis and other fields. However, in contrast, researchers have little understanding of the thermodynamic behavior of multi-element systems at the microscopic scale.
This is like discovering a class of new materials with many meaningful properties, but lacking understanding of how to regulate such materials, what the structure-activity relationship of such materials is, and so on, which underpins the underlying knowledge architecture system of the entire field.
In this work, the research results are only the tip of the iceberg of basic research on multi-system at the micro scale, and there is still a broad space for us to continue to explore and answer.
According to reports, Chen Pengcheng is particularly interested in basic research, and based on his previous research accumulation in the microscopic pluralistic system, he will continue to carry out in-depth exploration of basic science issues in this field in the future, so as to consolidate the academic community's understanding of basic science in this field.
Resources:
1.Chen, P. C., Gao, M., McCandler, C. A., Song, C., Jin, J., Yang, Y., ... & Yang, P. (2024). Complete miscibility of immiscible elements at the nanometre scale. Nature Nanotechnology, 1-7.
2. Science, 2016,352,1565;Science,2019,363,959
Operation/Typesetting: He Chenlong