Electrodeposited metal-organic framework films as self-assembled hierarchically superstructured supports for stable omniphobic surface coatings

Abstract

Superhierarchically rough films are rapidly synthesised on metal substrates via electrochemically triggered self-assembly of meso/macroporous-structured metal-organic framework (MOF) crystals. These coatings are applied to immobilise a functional oil with low surface energy to provide stable coatings repellent to a wide range of hydrophobic as well as hydrophilic fluids. Such omniphobic surfaces are highly interesting for several applications such as anti-fouling, anti-icing, and dropwise condensation, and become easily scalable with the presented bottom-up fabrication approach. As investigated by environmental scanning electron microscopy (ESEM), the presented perfluorinated oil-infused Cu-BTC coating constitutes of a flat liquid-covered surface with protruding edges of octahedral superstructured MOF crystals. Water and non-polar diiodomethane droplets form considerably high contact angles and even low-surface-tension fluids, e.g. acetone, form droplets on the infused coating. The repellent properties towards the test fluids do not change upon extended water spraying in contrast to oil-infused porous copper oxide or native copper surfaces. It is discussed in detail, how the presented electrodeposited MOF films grow and provide a proficient surface morphology to stabilise the functional oil film due to hemiwicking.

Preparation and Application of ZIF-8 Thin Layers

“…It seems clear that the surface chemistry and surface structure of the host layer has only little influence on the advancing contact angle, but a stronger influence on the resulting contact angle hysteresis. This can also be seen from the comparison with the reported contact angle values of HKUST-1 [33]. Compared to the ZIF-8 surfaces, the different surface of the HKUST-1 base structure leads to a slightly lower advancing water contact angle of 107 • but to a significantly higher water contact angle hysteresis of 101 • .…”

“…This is most likely due to the higher roughness of the e-coating compared to the surfaces fabricated with the doctor-blade technique. Compared to the values of HKUST-1 taken from the literature [33], a considerably smaller contact angle hysteresis was achieved with the ZIF-8 layers. Considering all the contact measurements, the fluid properties of the oil and the roughness of the base surface structure are the key…”

“…The results are shown in Table 1. For a better comparison, the roughness of a pure PVDF-layer was also measured and compared with the roughness parameters of HKUST-1 [33], which was deposited using electrochemical anodization as well. The average roughness of three different ZIF-8/PVDF composite layers is three to five times lower than that of the corresponding reference sample (HKUST-1) and is close to the value of the pure PVDF.…”

“…The results are shown in Table 2. Measurements on a PVDF layer and on a HKUST-1 layer (values taken from [33]) are included for comparison. The results show that oil infusion with GPL 105 leads to a low contact angle hysteresis for both water and diiodomethane.…”

“…The use of an MOF as host material for LIPS was first introduced in 2018, via electrodeposition of Cu-BTC HKUST-1 [33]. In this work, an electrochemically deposited layer of HKUST-1 was used as supportive host.…”