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Inkjet and spray coating process investigated with high-speed imaging

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Specialised Imaging reports on a technical article, written by researchers from the King Abdullah University of Science and Technology, Saudi Arabia - that describes the use of a Kirana ultra high-speed video system to undertake time-resolved imaging of a compressible air disk that forms under a drop impacting on a solid surface.

The capture of a bubble under an impacting drop can have detrimental effects on the uniformity of spray coatings and interfere with precision inkjet-based manufacturing such as are used in the printing of organic displays. When a drop impacts on a solid surface, its rapid deceleration is cushioned by a thin layer of air, which leads to the entrapment of a bubble under its centre. For large impact velocities the lubrication pressure in this air layer becomes large enough to compress the air.

In the article, researchers describe using the Kirana ultra high-speed video system, operating with 200 ns time-resolution, to directly observe the thickness evolution of the air layer during the entire bubble entrapment process. The initial disc radius and thickness shows excellent agreement with available theoretical models, based on adiabatic compression. For the largest impact velocities the air was compressed by as much as a factor of 14. Immediately following the contact, the air disc shows rapid vertical expansion. The radial speed of the surface minima just before contact, can reach 50 times the impact velocity of the drop.

Incorporating a proprietary hybrid camera sensor, the compact Kirana ultra high speed video camera can deliver high resolution and high speed (up to 5 million frames per second) in a no-compromise design. The full resolution of this video camera is maintained at all speeds. Comprehensive triggering facilities, highly accurate timing control and a wide range of output signals, coupled with a software package, simplifies image capture and analysis. Full remote operation using Ethernet connectivity comes standard enabling the Kirana to be easily integrated into almost any environment. The Kirana offers the performance, ease-of-use and operational flexibility that enables users to record and deliver impressive slow-motion video images in just about any scientific research application.