When particuology meets mesoscience--颗粒学报PARTICUOLOGY

Particuology, the name of this journal, was coined by the late Prof. Mooson Kwauk to define the science of studying various particles and their systems, including behavior of a single particle, interaction between particles, and behavior of a particle system consisting of many particles with other media. Since particle is the existent form of almost all solid materials, and gas bubbles and liquid droplets are also “particles” in a general sense, particuology represents quite a common knowledge for different engineering fields, therefore, is of special importance with transdisciplinary nature.

All disciplines follow a common practice that all problems to be studied are analyzed in the name of “system” which consists of many “elements”. These elements are usually simplified into “particles”, such as molecule particle, material particle, rock particle, and even beyond. Although these “particles” are different in size, shape, composition and property, studies on them are quite similar and commonly involve formation of a particle and its properties, interaction between particles, and the collective behavior of particles and their dependence on environment. In this regard, particuology is also quite a broad field.

The complexity of the real-world is embodied in the hierarchical natures of multilevels, each of the levels is multiscaled, consisting of element scale, system scale and the mesoscale in between element and system. Mesoscience is another transdisciplinary concept of science emerging recently to study all mesoscale phenomena, existing in between “element” (or small) scales and “system” (or large) scales at different levels, spanning elementary particles and the observable universe. It is to be devoted to exploring the universality of all mesoscales with the principle of compromise in competition between different dominant mechanisms governing a system, which was considered missing from the current knowledge base and leading to challenges in understanding complex systems. More details about this concept can be found in the joint virtual special issue entitled Towards Engineering Mesoscience, by the three journals of Chemical Engineering Science, Powder Technology and Particuology in 2013 (http://www.journals.elsevier.com/particuology/virtual-special-issue/engineering-mesoscience/).

Therefore, particuology and mesoscience, as two transdisciplinary sciences, are closely related to each other. Mesoscience is devoted to attacking the most critical issues at mesoscales in all fields including particuology, while particuology focuses on concrete problems in particle systems, and will contribute disciplinary evidences to mesoscience for deriving the universality of different mesoscale phenomena. Thus, mesoscience will facilitate the development of particuology.

Currently, like many other fields, particuology has accumulated much knowledge at the scale of single particles and the global behavior of a system scale. However, we know little at the mesoscale in between the particle scale and the system scale, where particles show collective and dynamic behaviors, resulting in heterogeneous structures both in time and in space, that is, the so-called complexity, which is exactly the topic for mesoscience. In the viewpoint of mesoscience, future particuology should shift much attention to the following aspects:

Particle design: In addition to chemical compositions, particle size, shape and surface are also critical to its properties and functions since these aspects influence not only its internal functions such as electron behavior but also external functions such as interaction with outsides. Understanding of the mechanisms of these influences is typically a mesoscale problem, challenging chemists and material scientists, and should be resolved jointly with particuologists.

Rational synthesis: In addition to chemistry knowledge, understanding of the compromise in competition between reaction and component transport in material synthesis processes is critical. At present, molecular self-assembly is related to this problem, unfortunately, the involvement of chemical engineering is not sufficient. Research in this aspect paid much attention to reaction kinetics even at molecular scale, but less to transport phenomena. That is, most of structures are currently studied with the assumption that the molecules of reactants are there where they are needed for combining with each others. This is obviously not right.

Smart production: Synthesis of a “structure” in chemistry is much easier than production of a material “product”. Currently, chemists and material scientists synthesize many structures day by day, but few of which can be massively produced as products. How can we solve this problem? Realization of specific conditions for products in a reactor is the key, which is directly subject to collective behavior of particles, showing dynamic heterogeneous changes in the reactor, which influence the transport processes, and hence, reaction. This is again another mesoscale problem at a higher level than that of molecular assembly.

Computer simulation: Conventional approaches might not be sufficient to solve the above three problems. Computation will be a powerful tool in realizing the so-called virtual process engineering of materials so that these problems can be studied with graphical simulation by generating the virtual reality of the whole process, opening a new paradigm for the research of particuology.

With the development of computational science and increasing knowledge at different levels involved, we will be able to attack the long-term challenging issues in particuology. The emerging mesoscience will accelerate this progress. This is something currently deserving special attention in particuology.

This editorial is in memory of the late Prof. Mooson Kwauk who founded the journal and served as the editor-in-chief for ten years until his passing away on November 20, 2012.

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