Velocity and size measurement of droplets from an ultrasonic spray coater using photon correlation spectroscopy and turbidimetry.

We have developed a combination of light scattering techniques to study and characterize droplets of an ultrasonic spray coater in flight. For this economically relevant spray coater, there is so far no reliable technique to systematically adjust the experimental parameters. We have combined photon correlation spectroscopy and turbidimetry to determine the size and speed of the droplets depending on parameters of the printing process as shroud gas pressure, flow rate, and atomizing power. Our method will allow us to predetermine these parameters to control the properties of the coated films as, e.g., thickness from tens of nanometers to micrometers.