Contact Angle Hysteresis with Different Wetting-liquids on Rough Surfaces

Contact angle hysteresis is a key parameter to determine the ease with which liquid breaks away from the solid surface. To study the contact angle hysteresis of different wettabilities, systematical experiments of Wenzel contact angle and contact angle hysteresis were conducted to characterize the wettabilities of strongly hydrophilic to hydrophobic liquids on three solid surfaces with quantitative surface roughness for the first time. Results obtained from the sessile drop and volume method tests were verified by the theories of Wenzel and static friction force, and used to reveal the relationship among Young contact angle, surface roughness and contact angle hysteresis. Results show that the contact angle hysteresis keeps constant in case of varied wettabilities of liquids on the surface of sample 1 (solid surface roughness, r=1.15). However, the contact angle hysteresis is maximum at theta(e)=90 degrees on the surface of sample 2 (r=1.64) and sample 3 (r=2.29), and decreases with increasing hydrophilicity and hydrophobicity of liquids. Besides, the effect of solid surface roughness on contact angle hysteresis depends on the wettability. The contact angle hysteresis decreases with increasing solid surface roughness when the wettability is hydrophilicity, while it presents no-obvious regularity in case of medium wettability.