Abstract Nanocrystalline Cu film with a mirror surface finishing is prepared by the electric brush-plating technique. The as-prepared Cu film exhibits a superhydrophilic behavior with an apparent water contact angle smaller than 10°. A subsequent increase in the water contact angle and a final wetting transition from inherent hydrophilicity with water contact angle smaller than 90° to apparent hydrophobicity with water contact angle larger than 90° are observed when the Cu film is subjected to natural aging. Analysis based on the measurement of hardness with nanoindentation and the theory of the bond-order-length-strength correlation reveals that this wetting variation on the Cu film is attributed to the relaxation of residual stress generated during brush-plating deposition and a surface hydrophobization role associated with the broken bond polarization induced by surface nanostructure.
Fund: Project supported by the National Natural Science Foundations of China (Grant No. 51371089) and the Foundation of National Key Basic Research and Development Program of China (Grant No. 2010CB 631001).
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