Individual aerosol droplets (25 – 300 µm) containing ammonium sulfate, polyethylene glycol (PEG) (O:C 0.56), and sorbitol (O:C 1.0) were placed on a hydrophobically coated slide. The ratio of PEG to sorbitol was varied to stay within an average O:C ratio of 0.56-0.71. For optical microscopy, the slide was placed in a flow cell with a humidity generator, and the radii of the core and shell were measured, as a function of ratio of PEG to sorbitol. For Raman microscopy, the slide was placed in a closed cell containing a saturated salt solution to obtain the desired relative humidity, and spectra were recorded in a 20x20 grid mapped the entire droplet.
LLPS only occurred when the average O:C ratio was between 0.56 and 0.71; however, the O:C ratio of the individual organic molecules determined where it resided during phase separation: lower O:C in the shell, higher O:C in the core with the ammonium sulfate. This result shows that there is not necessarily a strict separation between organic and inorganic species during LLPS.