Fabrication of hydrophobic surface on the gold and silver surface

Abstract

Recently, wettability has attracted much interest from researchers. It has significant relevance to many research field areas. For example, hydrophobicity is an important parameter in microfluidic applications. The lotus leaf has perfectly implemented the self-cleaning effect of a microstructured, hydrophobic surface. It is the model for synthetic surfaces with similar self-cleaning characteristics. Firstly, highly hydrophobic bare silver surface was fabricated. It was investigated that the roughness of the surface could be controlled through the electrodeposition kinetics. Silver surface with different roughness has been prepared through electrodeposition of silver zinc alloy and selectively zinc electrostripping. Three complex ions were used in electrodeposition of the alloy, including SCN-, I- and EDTA. After chemically identified by XRD, all three samples were confirmed to contain pure silver on the surface without trace of zinc. Correspondingly, different morphologies on prepared sample surfaces were obtained for samples involved with three different complex ions according to SEM images. In addition, the contact angle measurement showed that all three samples are remarkably hydrophobic. It was indicated that prepared pure silver surface with remarkable roughness exhibit highly hydrophobic properties. Secondly, by changing experiment condition, hydrophilic silver surface was also prepared through electrodeposition of silver zinc alloy and selective zinc electrostripping. However, after Self-assembled monolayer (SAM) modified the sample surface, the wettability transferred from hydrophilicity into hydrophobicity. The morphology for samples involved with electrodeposition using SCN- and I- is different from each other. Also, their morphologies are different from those with hydrophobic property. Seemingly, study was carried out to achieve hydrophobicity on the gold substrate by self-assembled monolayer modification. Two kinds of molecules were explored for this purpose. One is bromooctodecane and the other is octadecyltrichlorosilane (OTS). Self-assembled monolayer formed by bromooctodecane was characterized using CV and TOF-SIMS. Besides, it was proved by XPS that ultraviolet exposure improved the attachment of bromooctodecane on the gold surface. Although undesirable contact angle for SAM prepared from bromooctodecane molecules was obtained, this set a new direction for future study. In contrast, the SAM formed by octadecyltrichlorosilane (OTS) molecules exhibit remarkable hydrophobicity. It was generalized that the hydrophobicity changes with the immersition time in OTS solution, concentration of OTS solution and preservation time. Because multifunctional groups at the molecular head help molecules polymerize laterally, higher quality monolayer formed than thiols on gold surface.