title: Investigations of the hygroscopic properties of ammonium sulfate and mixed ammonium sulfate and glutaric acid micro droplets by means of optical levitation and Raman spectroscopy.
abstract: In the presented work an optical levitation technique performed by means of a focused laser beam, Mie and Raman spectroscopy have been utilized for measuring hygroscopic growth curves and composition of laboratory generated single ammonium sulfate (AS) and internally mixed ammonium sulfate-glutaric acid (GA) droplets in the micrometer range. The generated particles have been found to immediately supersaturate (above 45wt% for AS) at 297 K after capturing in the laser beam. Further increase of the relative humidity (RH) up to 85% does not dilute the droplets under the saturation point. A spontaneous hygroscopic growth takes place at 73.5-78% RH for pure AS. The particle grows with an average factor of 1.62 at the deliquescence relative humidity (DRH). Efflorescence of AS occurs at 43% RH with a corresponding concentration of more than 85wt%. Independent of the mixing ratios in ranges 25/75, 50/50, 75/25% AS/GA mixed particles don't exist as a metastable supersaturated solution droplets in the 35-85% RH range. Instead of growing with increasing relative humidity internally mixed particles build up a solid crystalline layer on the surface. This crystalline phase is not further influenced by ambient relative humidities.
authors.affiliation: R. Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 11, BG-1113 Sofia, Bulgaria. jordanb@cablebg.net
authors.forename: N
authors.initials: N
authors.lastname: Jordanov
authors.forename: R
authors.initials: R
authors.lastname: Zellner
mesh_terms: D000645:Ammonium Sulfate / Q000737:chemistry*; D005977:Glutarates / Q000737:chemistry*; D007834:Lasers; D008832:Microchemistry; D013059:Spectrum Analysis, Raman; D017155:Wettability
chemical_list: D005977:Glutarates; C035736:glutaric acid; D000645:Ammonium Sulfate