5.4.5.3 Wettability of Roughened Surfaces Wettability of a surface depends on the chemical nature of the liquid but can also be strongly affected by surface roughness [115-117]. The contact angle measurement and liquid break test were conducted to assess wettability of the liquids. The liquid break tests results of the roughened surfaces by imprinting of injection mould are summarised in Table 5.13.
Table 5.13 Liquid break test results of various materials roughen surface prepared by imprinting of injection mould
Materials Water Prevulcanised Latex Coagulant
PP-08, 24, 47, 80 Poor Partial Partial
PPTC20-08, 24, 47, 80 Poor Partial Partial
PPTC40-08, 24, 47, 80 Poor Partial Partial
COC-08, 24, 47, 80 Poor Good Good
PES-08, 24, 47, 80 Poor Good Good
Results of the liquid break test show that increasing of roughness did not improve the water wettability when compared to unroughened surface (see Table 5.7 and 5.13).…show more content… One was described by Wenzel [118] and the other by Cassie and Baxter [119]. Figure5.22 Wenzel model and Cassie-Baxter model
In the Wenzel model, the liquid is in contact with the entire solid surface and completely penetrates into cavities. The Wenzel model states that a rough material has a higher surface area than a smooth one, which modifies the contact angle according to the expression:
cos〖θ_W = r cos〖θ_Y 〗 〗
where W is the contact angle of liquid droplet on the rough surface, Y is the equilibrium contact angle on the smooth surface of the same material that can be described by Young’s equation, r is the surface roughness ratio defined as the actual area divided by its flat projected area.
For rough surface, r >