Abstract View
Dynamic Surface Tension of Surfactant Containing Droplets by the Oscillating Droplet Method
LARA LALEMI, Bryan R. Bzdek, Rachael E.H. Miles, University of Bristol
Abstract Number: 48
Working Group: Aerosol Chemistry
Abstract
Atmospheric aerosols cool the Earth’s climate by serving as cloud condensation nuclei. The extent of this cooling represents both the most uncertain and largest negative radiative forcing (countering the warming due to greenhouse gases) when predicting the Earth radiative budget. The barrier to cloud droplet activation is influenced by a particle’s surface tension. Surfactants are an important component of atmospheric aerosol mass, with recent atmospheric aerosol analyses in different regions showing the presence of surfactants at estimated concentrations as high as 27 ± 6 mM, resulting in predicted aerosol surface tensions <40 mN m-1. In this presentation, we explore the surface tensions of surfactant-containing microscopic droplets across a range of surfactant concentrations, droplet sizes, and surfactant types, quantifying the extent of surface tension reduction in droplets due to the presence of surfactants.
We use the oscillation approach to quantify the surface tension of aqueous surfactant solution droplets. 30-80 µm diameter droplets are reproducibly dispensed from a microdroplet dispenser with a surface age <1 ms. The resulting oscillations in droplet shape are characterised with 1 µs time resolution. The surface tension is inferred from the frequency of droplet oscillations, which are monitored in a time-resolved manner by stroboscopic imaging. The temporal development of the dynamic surface tension will be compared to bulk solution measurements to determine the effects of confinement on surface-bulk partitioning timescales. For 30 µm diameter droplets containing sodium dodecyl sulfate (SDS), surface tension reduction becomes more significant with increasing surfactant concentration. However, the magnitude of surface tension reduction is smaller than expected for a droplet at equilibrium owing to the short timescale of the measurement. The results provide valuable information about the timescales for surfactant partitioning in microscopic systems.