Bell-Shaped Superhydrophilic-Superhydrophobic-Superhydrophilic Double Transformation on a pH-Responsive Smart Surface

摘要

Smart surfaces, which exhibit stimuli-responsive changes in wetting properties, have drawn considerable attention in both fundamental research and industry owing to their promising applications in sensors, separators, microfluidic devices, drug delivery systems, and chemical valves. In particular, the ability of a surface to switch between super-hydrophobicity and superhydrophilicity is a focal point for the preparation of smart materials. To this end, various stimuli have been explored, including light, temperature, pH electric potential, solvent/solute,and coun-terions. Existing reports have described materials that undergo a single transformation of the contact angle (CA) in response to external stimuli. The transformation curve exhibits a Z or reverse Z shape, indicating that the wetting property of the material changes singly from superhydrophobicity to superhydrophilicity or from superhydrophilicity to superhydrophobicity. However, in applications such as intelligent separation, surfaces exhibiting a bell-shaped curve of wettability versus pH value, that is, surfaces with a sequential superhy-drophilicity-superhydrophobicity-superhydrophiliciry transformation, are preferred to selectively block an aqueous solution within a narrow response range to external stimuli. To our knowledge, no reports have described smart surfaces with two or more sequential responsive transformations during a single stimulation process.