Chemically Resolved Evaporation Dynamics of Dicarboxylic Acid Mixtures in Solid Particles

The evaporation rate and corresponding vapor pressureof dicarboxylicacids have been the subject of numerous scientific studies over theyears, with reported values spanning several orders of magnitude.Recent work has identified the importance of considering the phasestate of the material during evaporation, likely accounting for someof the variability in measured vapor pressures. In the homologousseries of dicarboxylic acids, the phase state under dry conditionsmay be crystalline or amorphous, with particles of odd-carbon-numberedacids exhibiting tendencies to remain amorphous and spherical. Althoughmeasurements of vapor pressures for pure components make up most ofthe available literature data, for many applications, these compoundsare not present in isolation. Additionally, many systems containinga semi-volatile material exist in a solid state, especially underdry and low relative humidity conditions. In this work, we explorethe evaporation of compounds present in mixed solid-state particles.Specifically, we use single particle levitation coupled with massspectrometry to measure the evolving composition of solid particlescontaining mixtures of glutaric acid and succinic acid, glutaric acidand adipic acid, and malonic acid and succinic acid. Under dry conditions,these systems exhibit non-spherical geometries consistent with crystallizationof one or both components into an organic crystal. Our measurementsallow the evaporation of each component in the mixture to be characterizedindependently and effective vapor pressures of the pure componentsto be inferred. The resulting vapor pressures are compared againstpure component vapor pressures. We demonstrate that these mixturesexhibit thermodynamic ideality but can be influenced by limited diffusionin the solid phase. These are the first results in the literaturethat explore the thermodynamic and kinetic factors that control theevaporative evolution of mixed solid-state particles.