Microchemistry: time dependence of an acid-base reaction in a single optically levitated microdroplet

Combining the optical levitation technique with Raman spectroscopy we were able to derive information on the chemical reaction of an acid microdroplet (droplet radius 7.5 μm) when exposed to ammonia. Of particular help were morphology-dependent resonances which are superimposed on the Raman spectrum, to follow the progress of growth and thickness of a salt coating performed by the microchemical acid-base reaction. Simultaneous measurement of the laser power needed to levitate the microparticle gave additional information on size and state of the particle as a function of time.