the effect of molecular structure on phase transitions of atmospheric aerosol particles

Organic aerosol particles are currently of great interest in atmospheric chemistry due to their chemical complexity and widespread abundance in the atmosphere. Organic aerosol particles play an important role in heterogeneous chemistry and cloud condensation nucleus formation. In the atmosphere, aerosol particles can undergo phase transitions (i.e. efflorescence, deliquescence and liquid-liquid phase separation), which are controlled by variables such as temperature, relative humidity, and the water solubility of a particular compound. We focused on studying two different series of compounds that were expected to undergo phase separation with similar molecular formulas (and organic:carbon, (O:C) ratios), but different molecular structures. We varied the relative humidity around the particles, which allowed for the comparison of phase transitions of aerosol particles with similar molecular formulas but different molecular structures. We used an environmental chamber to control the relative humidity, and an optical microscope equipped with a digital camera to image the laboratory generated aerosol particles. We observed that compounds with lower solubility values (≤7.24 g/100mL) underwent LLPS except for dimethyl succinate (7.06 g/100mL). We also observed that the presence of branching methyl groups in the main chain can lead to the absence of LLPS (e.g. 2,2-dimethylsuccinic acid). From this study, it is evident that for compounds with the same molecular formula, molecular structure may play an important role in how water interacts with the compound and leads to the presence or absence of LLPS.