The surface tension of surfactant-containing, finite volume droplets
Open Access
- 14 April 2020
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 117 (15), 8335-8343
- https://doi.org/10.1073/pnas.1915660117
Abstract
Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants in multiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.Keywords
This publication has 60 references indexed in Scilit:
- Impact of aerosols on convective clouds and precipitationReviews of Geophysics, 2012
- Surfactant effects in global simulations of cloud droplet activationGeophysical Research Letters, 2012
- Small amplitude shape oscillations of a spherical liquid drop with surface viscosityJournal of Fluid Mechanics, 2011
- Ternary solution of sodium chloride, succinic acid and water; surface tension and its influence on cloud droplet activationAtmospheric Chemistry and Physics, 2008
- Molar mass, surface tension, and droplet growth kinetics of marine organics from measurements of CCN activityGeophysical Research Letters, 2008
- Surfactant partitioning in cloud droplet activation: a study of C8, C10, C12 and C14 normal fatty acid sodium saltsTellus B: Chemical and Physical Meteorology, 2008
- Pharmaceutical Particle Engineering via Spray DryingPharmaceutical Research, 2007
- The role of surfactants in Köhler theory reconsideredAtmospheric Chemistry and Physics, 2004
- Pressure-volume-temperature-concentration relation of aqueous sodium chloride solutionsJournal of Chemical & Engineering Data, 1970
- VI. On the capillary phenomena of jetsProceedings of the Royal Society of London, 1879