Hamburg 2009 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 10: Poster: Umweltphysik
UP 10.26: Poster
Donnerstag, 5. März 2009, 17:48–19:00, VMP 9 Poster
Infrared Spectroscopy and Microscopy of Optically Levitated Droplets of Aqueous KCl Solutions Near the Crystallization Point — •Mariam Hamza2, Isik Riza Turkmen1, Mareike Brettholle1, Erwin Biller1, Bernhard Wassermann1, and Eckart Rühl1 — 1Physikalsiche Chemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin — 2Department of Physics, Suez Canal University, Kilo 4.5, Ismailia, Egypt
We report the novel FTIR spectra and results from optical microscopy of optically levitated microdroplets (10 - 20 um) containing saturated or dilute KCl salt solutions at room temperature. The relative humidities varied in the range of 50% - 70%. The initial concentrations of KCl in the dilute aqueous solutions were 1 M and 1.5 M . IR spectra were collected at different time intervals between particle injection and the time of crystallization. The IR band at ~ 3250 cm-1 is assigned to the OH stretching of salt solvated water. The increase in intensity of this band as a function of time is attributed to the increase of salt concentration in the droplet due to solvent evaporation. An abrupt increase in intensity of this band marks the critical concentration of KCl for the crystallization . In addition, micrographs of droplets were taken near the efflorescence point. It follows that initially transparent liquid droplets become opaque as soon as they crystallize. Therefore, the combination of optical microscopy and infrared spectra allow us for the first time to visualize the crystallization of small microparticles containing supersaturated salt solutions and extract the critical salt concentration that is required for crystallisation.