Essentially, as the surface is in the receding phase, the meniscus is traveling over a

previously wetted surface with a different surface energy than before. Due to this

phenomenon, the advancing contact angle can be considered a measure of the low-energy

portion of a heterogeneous surface and receding angles are more characteristic of high-

energy parts.[125] In examining Table 3.8, one aspect that stands out is the small hysteresis

of the 20% 5000 cSt samples. This is most likely attributed to the fact that these samples

had a visible coating of oil on the surface, which may mask the rearrangement process, or

at least minimize the effects.




Table 3.8 DCA data on silicone elastomer modified with non-functionalized PDMS
oligomers
 Viscosity Wt. % 0adv 0rec AO
 Unmodified 0 115.1 3.8 68.7 2.2 46.4 1.7
 50 cSt 5% 113.9 1.8 77.5 1.8 36.4 0.3
 50 cSt 20% 100.5 + 1.3 65.1 + 2.1 35.4 + 1.6
 5000 cSt 5% 106.1 + 0.7 71.6 2.2 34.5 2.1
 5000 cSt 20% 101.0 +0.8 89.4 4.4 11.6 4.4


 Figure 3.10 is an example of a force-distance curve taken on a textured substrate.

The sample advances into a smooth area, and then into an area of texture. At the end of

the advancing dip, the sample is retracted through the textured area and then on to the

smooth area. Several factors preclude the presentation of numerical results for this study.

For many samples, the lengths of smooth and textured areas were not long enough to

achieve a linear region of stable contact angles. In addition, the varying thickness and the

fact that only one side of samples were textured make numerical contact angles

unreliable. However, for the majority of the samples, the trend was similar. The

advancing textured areas had higher contact angles than the smooth areas, while the