title: Facile spray-coating process for the fabrication of tunable adhesive superhydrophobic surfaces with heterogeneous chemical compositions used for selective transportation of microdroplets with different volumes.
abstract: In this paper, tunable adhesive superhydrophobic ZnO surfaces have been fabricated successfully by spraying ZnO nanoparticle (NP) suspensions onto desired substrates. We regulate the spray-coating process by changing the mass percentage of hydrophobic ZnO NPs (which were achieved by modifying hydrophilic ZnO NPs with stearic acid) in the hydrophobic/hydrophilic ZnO NP mixtures to control heterogeneous chemical composition of the ZnO surfaces. Thus, the water adhesion on the same superhydrophobic ZnO surface could be effectively tuned by controlling the surface chemical composition without altering the surface morphology. Compared with the conventional tunable adhesive superhydrophobic surfaces, on which there were only three different water sliding angle values: lower than 10°, 90° (the water droplet is firmly pinned on the surface at any tilted angles), and the value between the two ones, the water adhesion on the superhydrophobic ZnO surfaces has been tuned effectively, on which the sliding angle is controlled from 2 ± 1° to 9 ± 1°, 21 ± 2°, 39 ± 3°, and 90°. Accordingly, the adhesive force can be adjusted from extremely low (∼2.5 μN) to very high (∼111.6 μN). On the basis of the different adhesive forces of the tunable adhesive superhydrophobic surfaces, the selective transportation of microdroplets with different volumes was achieved, which has never been reported before. In addition, we demonstrated a proof of selective transportation of microdroplets with different volumes for application in the droplet-based microreactors via our tunable adhesive superhydrophobic surfaces for the quantitative detection of AgNO3 and NaOH. The results reported herein realize the selective transportation of microdroplets with different volumes and we believe that this method would potentially be used in many important applications, such as selective water droplet transportation, biomolecular quantitative detection and droplet-based biodetection.
authors.affiliation: Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Gansu Polymer Materials, College of Chemistry and Chemical Engineering, Northwest Normal University , Lanzhou 730070, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.forename: Zhijiao
authors.initials: Z
authors.lastname: Jing
authors.forename: Fei
authors.initials: F
authors.lastname: Zha
authors.forename: Yaoxia
authors.initials: Y
authors.lastname: Yang
authors.forename: Qingtao
authors.initials: Q
authors.lastname: Wang
authors.forename: Ziqiang
authors.initials: Z
authors.lastname: Lei
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D053758:Nanoparticles / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D013499:Surface Properties; D014961:X-Ray Diffraction; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D015034:Zinc Oxide