Comparative study of the dynamic hydrophobicity of fluoroalkylsilane coatings tilted at acute and obtuse angles

• Published in: JCT research Vol. 15; no. 4; pp. 891 - 898
• Main Authors: Higashino, Yuta, Takahashi, Hirokazu, Sakai, Munetoshi, Isobe, Toshihiro, Matsushita, Sachiko, Nakajima, Akira
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-07-2018; Springer Nature B.V
• Subjects: Brief Communication; Chemical vapor deposition; Chemistry and Materials Science; Coatings; Contact angle; Corrosion and Coatings; Dependence; Drag; Droplets; Hydrophobicity; Industrial Chemistry/Chemical Engineering; Materials Science; Organic chemistry; Polymer Sciences; Silicon substrates; Sliding; Surfaces and Interfaces; Thin Films; Tribology; Velocity; Viscous drag; Water drops; Sliding; Droplet; Obtuse angle; Hydrophobic
• ISSN: 1547-0091; 1935-3804; 2168-8028
• DOI: 10.1007/s11998-018-0064-5

The relation between surface homogeneity and internal fluidity for a droplet sliding on a surface tilted at acute and obtuse angles was investigated using two hydrophobic fluoroalkylsilane (FAS) coatings with different roughness. The coatings (FAS-smooth and FAS-rough) were prepared on an Si substrate using chemical vapor deposition or soaking methods and were tilted at 35° or 145°. Sliding velocity of water droplets on the surface tilted at 145° was greater than that tilted at 35° for both coatings. For 35° tilting, the dominant mode of the sliding velocity was slipping for FAS-smooth, whereas rolling governed the entire sliding velocity for FAS-rough. The slipping mode was more important than the rolling one for both coatings when they were tilted at 145°. The change of slipping velocity was more remarkable than that of rolling one for both coatings between 35° and 145° tilting. Results show that the difference in gravity direction and contact area of the droplets contributed to this tilt angle dependence of the sliding velocity. When a droplet slid down with acceleration on FAS-smooth surface, the coefficient of the viscous drag force correlated with the velocity ratio (
U
total
/
U
slip
).