Low-Cost, In-Situ Surface Tension Measurements of Hanging Aerosol Mimic Droplets under Controlled Atmospheric Conditions

BRUNO LOYOLA SAN MARTIN, Michael Haines, Tzu-An Kuan, Joseph Woo, Lafayette College

     Abstract Number: 618
     Working Group: Instrumentation and Methods

Abstract
Hanging droplet experiments of aerosol mimic solutions are useful due to their unique combination of measurable surface phenomena on geometries approximating aerosols and working solution volumes sufficient for straightforward condensed-phase characterization (e.g. refractometry, mass spectroscopy, UV-visible absorbance) without additional processing. While the governing equations for pendant drop tensiometry are well-established, consistent control of ambient conditions around a hanging droplet can prove non-trivial to reliably implement. This work compares time-resolved surface tension measurements of aqueous aerosol mimic solutions using a pendant drop tensiometer constructed from 3D printed parts and a webcam against a research-grade profile analysis tensiometer. Measurements of hanging droplets exposed to controlled concentrations of water vapor and low-mass VOCs (e.g. ethanol, isopropanol, etc. are assessed. Scripted exposure sequences that induce multiple, scheduled step-change shifts to droplet ambient gas-phase compositions around hanging droplets are performed. Using this approach, first-order step responses to measured surface tension are observed.