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Aerosols are key components of the atmosphere and play important roles in many industrial processes. Because aerosol particles have high surface-to-volume ratios, their surface properties are especially important. However, direct measurement of the surface properties of aerosol particles is challenging. In this work, we describe an approach to measure the surface tension of picoliter volume droplets with surface age <1 ms by resolving their dynamic oscillations in shape immediately after ejection from a microdroplet dispenser. Droplet shape oscillations are monitored by highly time-resolved (500 ns) stroboscopic imaging, and droplet surface tension is accurately retrieved across a wide range of droplet sizes (10-25 μm radius) and surface ages (down to ∼100 μs). The approach is validated for droplets containing sodium chloride, glutaric acid, and water, which all show no variation in surface tension with surface age. Experimental results from the microdroplet dispenser approach are compared to complementary surface tension measurements of 5-10 μm radius droplets with aged surfaces using a holographic optical tweezers approach and predictions of surface tension using a statistical thermodynamic model. These approaches combined will allow investigation of droplet surface tension across a wide range of droplet sizes, compositions, and surface ages.
Bibliographical noteFunding Information:
B.R.B. acknowledges support from the Natural Environment Research Council (NERC) through Grant No. NE/P018459/ 1. R.E.H.M. and J.S.W. acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC) through Grant No. EP/N025245/1. H.C.B. and C.S.D. acknowledge support from the National Science Foundation (NSF) under Grant No. 1554936; the College of Science and Engineering Characterization Facility, Uni- versity of Minnesota, which receives funding from the NSF through the UMN MRSEC under Award No. DMR-1420013; and support for H.C.B. through a National Science Foundation Graduate Research Fellowship through NSF Grant No. 00039202. Ivo Videnov is acknowledged for holographic optical tweezers measurements on the 4:1 and 16:1 sodium chloride/glutaric acid mass mixtures.
Bryan R. Bzdek is a NERC independent research fellow at the University of Bristol. He earned a B.S. degree in chemistry at Bucknell University (2008) and performed undergraduate research with Molly McGuire. He earned a Ph.D. degree in chemistry with Murray Johnston at the University of Delaware (2014). He performed postdoctoral research with Jonathan Reid at Bristol (2014−2017) before starting his independent career at Bristol. His interests include development of single particle approaches to study aerosol physicochemical properties. His work in aerosol science has been acknowledged by the American Association for Aerosol Research through the Sheldon K. Friedlander Award (2017).
© 2019 American Chemical Society.
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 6
PubMed: MeSH publication types
- Journal Article