Surface-Area-to-Volume Ratio Determines Surface Tensions in Microscopic, Surfactant-Containing Droplets

The surface composition of aerosol droplets is central to predicting cloud droplet number concentrations, understanding atmospheric pollutant transformation, and interpreting observations of accelerated droplet chemistry. Due to the large surface-area-to-volume ratios of aerosol droplets, adsorption...

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Bibliographic Details
Published in:ACS central science 2023-11, Vol.9 (11), p.2076-2083
Main Authors: Bain, Alison, Ghosh, Kunal, Prisle, Nønne L., Bzdek, Bryan R.
Format: Article
Language:English
Subjects:
Acids
Aerosols
Agreements
Air pollution
Atmospheric aerosols
Chemical reactions
Droplets
Pollutants
Surface tension
Surfactants
Thermodynamic models
Trends
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Summary:The surface composition of aerosol droplets is central to predicting cloud droplet number concentrations, understanding atmospheric pollutant transformation, and interpreting observations of accelerated droplet chemistry. Due to the large surface-area-to-volume ratios of aerosol droplets, adsorption of surfactant at the air–liquid interface can deplete the droplet’s bulk concentration, leading to droplet surface compositions that do not match those of the solutions that produced them. Through direct measurements of individual surfactant-containing, micrometer-sized droplet surface tensions, and fully independent predictive thermodynamic modeling of droplet surface tension, we demonstrate that, for strong surfactants, the droplet’s surface-area-to-volume ratio becomes the key factor in determining droplet surface tension rather than differences in surfactant properties. For the same total surfactant concentration, the surface tension of a droplet can be >40 mN/m higher than that of the macroscopic solution that produced it. These observations indicate that an explicit consideration of surface-area-to-volume ratios is required when investigating heterogeneous chemical reactivity at the surface of aerosol droplets or estimating aerosol activation to cloud droplets.
ISSN:2374-7943
2374-7951
DOI:10.1021/acscentsci.3c00998