The detection of μm and sub-μm droplets of aqueous solutions of sodium chloride and sodium sulfate

Abstract

μm and sub-μm droplets of aqueous NaCl and Na 2SO 4 solutions were quantitatively identified by a chemical spot technique using thin and ultra-thin films of polyvinyl alcohol-reagent mixture. A comparison has been made between theoretical and experimental calibration curves under various conditions with respect to the thickness of the film and different reagent concentration for the detection of chloride or sulfate. Droplets generated by the atomization of aqueous NaCl or Na 2SO 4 solution were collected on these polyvinyl alcohol-reagent films. The spots impressed on the films were measured by an optical microscope. Calibration curves relating the spot and droplet diameters were experimentally measured. It was found that each of the calibration curves could be expressed by a relation D d 3 = Kd 2 s , where D d is the volume average diameter of the droplets, d s the surface average diameter of the spots and K is a calibration curve constant. The meaning of K is discussed. A linear relationship has been found between the ratio of an experimental calibration curve constant to a theoretical one and the concentration of the reagent in the film. Then the following equation was obtained: K (exptl) K (theor.) = 0.29A , where A is the concentration of the reagent in the film (molℓ −1). This equation is useful in estimating the values of different experimental calibration curve constants. The minimum diameter of the droplets that can be identified by this technique is 0.2 μm.