Spray coating techniques are used to obtain thin films by the formation of fine droplets of the coating solution that are deposited on the substrate. In spray coating devices, pressurized air is used to atomize the liquid flow coming from the syringe into small droplets. These droplets are then deposited on the substrate, where they form the coating.
Ultrasonic spray coating technique uses sound vibrations to sonicate the coating solution into a mist of very small droplets. This allows a more homogeneous distribution of the droplets, and this is why is sometimes preferred to spray coating using air . The resulting droplets size is in the micrometer range, leading to a good reproducibility of the coatings. A formula for the size diameter of droplets produced by ultrasonic atomization was proposed by Lang :
Where ρ is the liquid density, σ the surface tension and f the frequency.
A good study of the parameters that affect the droplets size can be found in .
In order to obtain uniform films, the parameters of the process should be carefully controlled. The main parameters that affect ultrasonic spray coating are the substrate, the solvent used, the spray path, the flow rate of the solution, the temperature of the substrate, the speed of the nozzle, the frequency, the distance between nozzle and substrate, the air pressure…
Basic ultrasonic spray coating setting. © Nadetech Innovations
 Bose, S., Keller, S. S., Alstrøm, T. S., Boisen, A., & Almdal, K. (2013). Process optimization of ultrasonic spray coating of polymer films. Langmuir, 29(23), 6911-6919.
 Lang RJ . Ultrasonic atomization of liquids . The journal of the acoustical society of America . 1962 ; 34 : 6 – 8
 Dalmoro, A., d’Amore, M., & Barba, A. A. (2013). Droplet size prediction in the production of drug delivery microsystems by ultrasonic atomization. Translational Medicine@ UniSa, 7, 6.
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