Measuring Surface Tension of Single Aerosol Particles Using Electrodeformation

THOMAS PRESTON, McGill University

     Abstract Number: 73
     Working Group: Instrumentation and Methods

Abstract
Surface tension measurements are key to understanding the behaviors of atmospheric aerosols, especially concerning their role in cloud droplet formation and activation. Conventional tensiometry tools encounter significant difficulties with metastable states relevant to aerosols (e.g. supercooled, supersaturated) due to large sample volumes and the presence of surfaces. This work introduces an instrument designed to measure surface tension in a non-contact, humidity-controlled setting by employing a strong electric field to deform aerosol microdroplets.

Our method uses a dual-beam optical trap to hold single microdroplets between two electrodes. Upon application of a high voltage across the electrodes, microdroplets exhibit deformations on the order of tens of nanometers. These deformations are quantified through the analysis of morphology-dependent resonances that appear as sharp peaks in Raman spectra. This technique allows for the precise determination of surface tension in aqueous droplets containing inorganic and organic solutes commonly found in atmospheric aerosol particles.

We focus on water activities that correspond to supersaturated conditions, a domain largely unexplored due to measurement challenges. Our findings, where they can be compared to existing data, align well with previous results. The instrument, which does not depend on dynamic processes, is also capable of measuring surface tension in systems with viscosities exceeding 100 Pa·s, representing a major advancement over previous levitation-based methods.