Measurement Procedures and Details

3 Determination of Sliding Angle 2.3.1 Measurement Procedures and Details 

2 Contact Angle Measurements and Surface Characterization Techniques 

The retention force or friction that keeps the drop from sliding is / and is given by [44]  

As the tilt angle continues to increase, the drop shape is distorted further, curve 1 to 2 in Fig. 2.12b. When F =/, the drop begins to move and the tilt angle is recorded as a. 

The criteria to determine if a drop starts to move is very subjective. Since the drop will only start to slide when the contact line at the trail edge is de-pinned, it would be very helpful to place a tiny droplet of a nonvolatile Uquid next to the trial edge as a positional reference. The volume of the reference drop is so small that it will never move during tilting. By carefully examining the distance between the reference drop and the trail edge, one can easily capture the moment when the drop starts to slide. 

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