Recent advances in experimental techniques for investigating aerosol surface tension

The small size and contactless environment of aerosol droplets results in unique surface compositions compared to macroscopic solutions. The large surface-area-to-volume ratio possessed by aerosol droplets can lead to a difference in the partitioning of surface-active molecules between macroscopic solutions and droplets, even when the total composition remains unchanged. Additionally, suspended aerosol droplets can become supersaturated and supercooled, affecting the droplet's surface tension. The importance of the surface tension of aerosol droplets has garnered much attention in the past years in diverse contexts including aerosol-assisted materials synthesis, respiratory aerosol dynamics, and atmospheric aerosol processes. To understand the implications of surface-area-to-volume ratio, supercooling, and supersaturation on aerosol surface tension a variety of new tools and techniques have been developed to measure the surface tension directly in the droplet phase. In this review, we will introduce the techniques used in the field to measure the surface tension of aerosol droplets, provide insight into the strengths of various techniques, and describe the types of measurements that these techniques have been used to make. Finally, we provide an outlook on the types of measurements that should be prioritized now that we have an arsenal of measurement techniques available.