Combining weighting and scatterometry: Application to a levitated droplet of suspension

Two optical methods of droplet radius measurement were combined with droplet weighting. The applicability of such combination to droplets of liquids and liquid suspensions was investigated. The combination was successfully tested for a mixture of two glycols. It was checked that droplet radius evolution may be obtained with good accuracy by weighting. Since weighting is not a stand-alone method, it was calibrated in a small region with an optical method. Droplet electrical charge is the parameter obtained from the calibration. The application of the combination of methods to a droplet of suspension was demonstrated on droplets of suspensions of polystyrene nano-spheres in diethylene glycol, evolving from moderate/high concentration to a nearly dry agglomerate particle. A detailed analysis of the results obtained from all the three methods may provide information on the changing density, effective refractive index, electric charge and the internal structure of the droplet.

► We propose to combine droplet weighting with two optical methods of radius measurement. ► The combination is efficient for characterisation of droplets of suspension. ► Droplet electrical charge can be found. ► The evolution of internal droplet structure can be inferred.