This article discusses the basics of particle morphology and its processes while providing information regarding atmospheric aerosols and the recent advances in this particular field.
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What is Particle Morphology?
Particle morphology involves the analysis of the size, shape, orientation, size distribution, particle growth profile, physiochemical structure, roundness, aspect ratio, diameter, and structural buildup. The size, texture, and/or surface pattern of primary particles may frequently provide essential knowledge regarding the nature and provenance of particulate matter.
Optimizing particle morphology by altering the catalytic and reaction parameters has sparked great interest among academics and in industry. From an industrial standpoint, excellent particulate morphology often entails round form, optimum size distribution, higher surface bulk density, regulated percentage of pores and intrinsic composition, and so on.
Techniques of Particle Morphology
The most popular techniques are atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Apart from these conventional methods, modern novel techniques involve nanoparticle track analysis (NTA), fluorescence correlation spectroscopy (FCS), laser-induced breakdown detection (LIBD), single particle counter (SPC), small-angle X-ray scattering (SAXS), and scanning X-ray disc centrifuge (SDC), but the majority are still in the early stages of development.
These unique methods are specialized morphology study techniques for nanomaterials. A survey of recent publications reveals that dynamic light scattering (DLS) for particle size, typically in combination with ζ-potential (zeta-potential) investigations, and transmission electron microscopy (TEM) for geometry and morphological characterization, are the most extensively employed methods.
Importance of Particle Morphological Studies
Having a thorough understanding of particle morphology and how it responds to external stimuli is critical in several geotechnical and commercial processes. Applications include foundation engineering, particle piercing, materials science, the biomedical sector, nanoparticle characterization, the biomass business, and, most crucially, the structural engineering industry.
The variation of size, shape, bonding forces, intramolecular orientation, and other factors drastically alter the mechanical and chemical properties such as load-bearing capacity, young’s modulus, ultimate tensile stress, etc. Before performing any sort of experimental analysis, the morphological analysis provides a firm foundation regarding the comprehension of material behavior and chemical reactivity.
The importance of particle shape in any particular application will vary greatly. If powdered materials are being synthesized for optimum flowability, spherical or round morphology would be deemed ideal for this purpose. Alternatively, if the purpose is to generate something abrasive, the particle form must be highly angular.
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Limitations of Particle Morphology
Although particle morphology studies seem to be ideal in providing essential information regarding various mechanical properties, certain limitations and disadvantages have to be kept in mind while progressing further. It should be emphasized that poor idealization of both data accuracy and particle morphology (i.e., particle size) contributes to incorrect findings.
Since particle morphology utilizes imaging on the micro and nanoscale, glare and other imaging shadows might result in incorrect interpretation of the results leading to inaccurate assumptions for the intended experiment. Apart from this, a major concern is that the instruments utilized for this purpose are highly expensive and a few processes are highly sensitive and time-consuming.
The accurate calibration of the instruments along with the maintenance costs is another issue that is integrated with such processes. Even though these issues exist, still particle morphology study is considered the best technique to identify and characterize structural particles for research purposes.
Introduction to Atmospheric Aerosols
Aside from gases, the environment contains a range of liquids and solids that reside in the air as distributed forms. They are known collectively as aerosols. An aerosol is a two-phase network made up of solid and liquid particles and the gas (air) in which they are embedded.
Aerosols are produced by both natural and artificial causes. Both natural aerosols and artificial ones have a substantial climate impact by influencing the Earth's thermal equilibrium, cloud formation, and chemical metabolism. Particular atmospheric particulate morphology (form, mass, and structural properties), as well as the mixing phase, determine their photocatalytic activity as well as their relationships with clouds, and hence their meteorological parameters.
Latest Research Findings
The latest research by Mr. Yang and his team published in the journal Aerosol and Air Quality Research is focused on the measurements of aerosol particles through an investigation of the morphology and density of single black carbon atmospheric aerosols. As per the research, air pollution from aerosolized black carbon (BC) has a negative impact on air transparency, temperature, and health. To evaluate the mixing conditions and aging process of BC particles, particle density and shape are frequently required.
To calculate the concentration and dynamic shape factor (χ) of atmospheric BC particulate with 3 distinct aerodynamic diameters (Da, 200 nm, 350 nm, and 500 nm) in Shanghai, China, a typical urban area, a technique integrating an aerodynamic aerosol classifier (AAC), a differential mobility analyzer (DMA), a single-particle soot photometer (SP2), and a single particle aerosol mass spectrometer (SPAMS) was developed.
These BC-dominated particles showed a near-spherical morphology ( 1.02), suggesting that they had experienced fast morphological alteration from an extremely unusual morphology to a near-spherical shape. The majority of BC particles with Da of 350 nm or 500 nm were BC-mixed nanoparticles.
Incorporating effective densities (1.62–1.77 g cm–3) and ordinary single-particle spectral data, ammonium sulfate and ammonium nitrate were discovered to be the important pre-dominant compounds of these BC-mixed particulates, implying that supersaturation of inorganic constituents such as nitrates and sulfates could play a major role in the aging process of fresh BC in Shanghai.
In short, the process of particle morphology is essential for almost all industries, and its significance for identifying the optimum atmospheric aerosol concentration and mixing ratio is unparalleled.
References and Further Reading
Wang, Shurong et al. 2021. Measurement of Density and Shape for Single Black Carbon Aerosols in a Heavily Polluted Urban Area. AEROSOL AND AIR QUALITY RESEARCH. 21(12). Available at: https://aaqr.org/articles/aaqr-21-07-oa-0162
Wang, Shurong et al. 2022. Online shape and density measurement of single aerosol particles. Journal of Aerosol Science. 159. 105880. Available at: https://www.sciencedirect.com/science/article/pii/S0021850221006091?via%3Dihub
Ott, Emily-Jean E., and Miriam Arak Freedman. 2021. Influence of Ions on the Size Dependent Morphology of Aerosol Particles. ACS Earth and Space Chemistry. 5(9). 2320-2328. Available at: https://pubs.acs.org/doi/10.1021/acsearthspacechem.1c00210
Lei, Ziying. 2021. The Role of Acidity, Viscosity, and Morphology on Atmospheric Aerosol Physicochemical Properties and Impacts. Diss. Available at: https://deepblue.lib.umich.edu/handle/2027.42/169919
Lee, Hansol D., and Alexei V. Tivanski. 2021. Atomic force microscopy: an emerging tool in measuring the phase state and surface tension of individual aerosol particles. Annual review of physical chemistry. 72. 235-252. Available at: https://www.annualreviews.org/doi/10.1146/annurev-physchem-090419-110133
Wang, Yuanyuan, et al. 2021. Constructing shapes and mixing structures of black carbon particles with applications to optical calculations. Journal of Geophysical Research: Atmospheres. 126(10). Available at: https://pubs.acs.org/doi/10.1021/acs.analchem.0c05225
Hsiao, Ta-Chih, et al. 2021. Effect of particle morphology on performance of an electrostatic air–liquid interface cell exposure system for nanotoxicology studies. Nanotoxicology. 15.4 (2021): 433-445. Available at: https://www.tandfonline.com/doi/full/10.1080/17435390.2020.1863499