Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods

[摘要] Measurements of a single, levitated particle in an electrodynamicbalance are an established tool for deriving thermodynamic andmaterial data such as density, refractive index and activities ofcomponents of an aqueous solution under supersaturated conditions,where bulk measurements are not possible. The retrieval relies oncombining mass-to-charge data and size data from light scattering.Here, we use a combination of low- and high-resolution Mie resonancespectroscopy to obtain radius data, enabling an accurate sizedetermination not only when the particle is in equilibrium, but alsowhen it is out of equilibrium due to kinetic limitation of masstransport. With the data measured under non-equilibrium conditions, itis possible to retrieve the water diffusivity. A challenge is that theradius retrieval by comparing measured light scattering with Mietheory requires the knowledge of refractive index as a function ofconcentration. Here, we show an iterative retrieval of refractiveindex and size for compounds for which data cannot be obtained in thebulk either due to lack of sufficient amounts of sample or limitedsolubility. We demonstrate the measurement strategy and the retrievalof water activity, density, refractive index and water diffusivity foraqueous shikimic acid. Water diffusivity in concentrated shikimic aciddecreases by 6 orders of magnitude at 250K compared to thatat room temperature.

[学科分类] 几何与拓扑