Influence of the Processes Parameters on the Properties of The ...

Chapter 4.
Experimental Procedures and Protocols for Analyses
3.3 Contact Angle Measurement
The used apparatus Digidrop Contact Angle GBX (cf. Figure 4.20) makes it possible to carry out
measurements <strong>of</strong> contact angle per drop posed on substrate by recording image per image <strong>of</strong> <strong>the</strong> sessile drop.
The drop is allowed to flow and equilibrate with <strong>the</strong> surface.
(A)- Apparatus
(B)- Syringe with
specific liquids
(C)- Liquid deposition sequence
Figure 4.20: Goniometer GBX used for contact angle measurement.
This goniometer is constituted by:
A motorized movable plate on which a compressed powder pellet is deposited,
A light source and a digital CCD camera that can acquire photographs <strong>of</strong> <strong>the</strong> system drop / solid at
equilibrium (24 frames/sec),
A motorized syringe to deposit a liquid drop, volume controlled from <strong>the</strong> surface <strong>of</strong> <strong>the</strong> solid sample
to be analyzed,
An acquisition system to record wetting angle and process photographs using <strong>the</strong> s<strong>of</strong>tware on digital
images DIGIDROP.
Two different fitting procedures have been used to determine <strong>the</strong> best shape <strong>of</strong> <strong>the</strong> drop and thus
<strong>the</strong> correct contact angle (cf. Figure 4.21). The contour method toge<strong>the</strong>r with <strong>the</strong> height-width approach, are
appropriate for small contact angle measurements. The circle-method shapes <strong>the</strong> drop in <strong>the</strong> form <strong>of</strong> a
circular arc, while <strong>the</strong> height-width-method determines <strong>the</strong> height and <strong>the</strong> width <strong>of</strong> a rectangle that surrounds
<strong>the</strong> drop.
A manual method, <strong>the</strong> tangent-method or <strong>the</strong> conic section method, fits a conic section equation
on <strong>the</strong> drop shape where θ acts as <strong>the</strong> angle at <strong>the</strong> three-phase contact point. A benefit here is that <strong>the</strong> contact
angle range is much wider (between 10 and 100°), and that <strong>the</strong> fitting procedure does not assume that
contact angles on both sides are equal, resulting in two different contact angles (θ left and θ rigth ).
(A)
(B)
Figure 4.21: (A): Schematic diagram and (B): Two methods for determining <strong>the</strong> contact angle.
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