American Association for Aerosol Research - Abstract Submission

AAAR 37th Annual Conference
October 14 - October 18, 2019
Oregon Convention Center
Portland, Oregon, USA

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Surface Tensions of Picoliter Droplets with Sub-Millisecond Surface Age

BRYAN R. BZDEK, Rachael E.H. Miles, Michael Glerum, Hallie Boyer, Jim Walker, Jonathan P. Reid, Cari Dutcher, University of Bristol

     Abstract Number: 35
     Working Group: Aerosol Physics

Abstract
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 to their reactivity and cloud droplet forming potential. However, direct measurement of the surface properties of aerosol particles is challenging. In this work, we describe a new 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. Experimental results from the microdroplet dispenser approach are compared to complementary measurements of the surface tension 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. The approach was then applied to study surfactant partitioning in freshly produced picoliter droplets on microsecond timescales. These approaches combined allow investigation of droplet surface tension across a wide range of droplet sizes, compositions, and surface ages.