Enhancing Hydrophobicity of Polymer Thin Film-Coated Surface by Wrinkling Method

The hydrophobicity of film surfaces can be enhanced by introducing wrinkling and buckling, and the wrinkling method in this study is a facile way to induce various microstructures including wrinkles and buckles in film surfaces. When buckles formed, the water contact angle parallel to the wrinkled direction (θ//) changed dramatically with strain, but the contact angle perpendicular to the wrinkled direction did not change much. It was found that the buckle structural feature was the key characteristics affecting the change in contact angle, θ//. A dimensionless number, the ratio of buckle height to spacing (Hb/Sb) was introduced to determine the relationship between the structural feature and the contact angle, θ//. The contact angle, θ// strongly depended on Hb/Sb. The thickest film (hf = 605 nm) at the highest strain (ɛ = 30%) and the highest Hb/Sb formed many large buckles, and exhibited super-hydrophobicity (θ// = 169 ± 10°).