Determination of Contact Angle from Contact Area of Liquid Droplet ...

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Determination of Contact Angle from Contact Area of Liquid Droplet Spreading on Solid Substrate
Derrick O. NJOBUENWU, Esio O. OBOHO, Rhoda H. GUMUS
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Figure 3. Experimental setup to measure contact angle from contact area: 1, Flat solid
substrate; 2, Optical screen; 3, Microlitre screen; 4, Micromanipulator; 5, CCD video
camera; 6, VHS recorder; 7, Light source; 8, Personal computer with frame grabber; 9
spreading drop
Results and Discussion
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The spreading of liquid droplets over glass, polystyrene and PMMA substrates were
investigated. Typical image frame acquired by the image analysis system described in the
experimental procedure is displayed in Figure 4. The figure shows a printout of the plan view
of a sample of experimental measurement for silicone oil spreading on glass substrate.
Similar images (frames) were grabbed by the image analyser for glycerine and hexadecane
drops on glass, polystyrene and PMMA substrate. The radius of spread was determined by the
plan view and the contact angle for spreading of liquid droplets was determined from the side
view. These data were digitalised and measured using the software as a function of time. The
omissions of the other images were deliberate to avoid redundancy of images. Furthermore, a
surface plot of a frame for Glycerine on Polystyrene is shown in Figure 5 to elucidate the
understanding on surface geometry of liquid droplet undergoing partial wetting on solid
substrate surface.
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