Wettability tailoring of nanotube carpets: morphology-chemistry synergy for hydrophobic–hydrophilic cycling

Abstract

Carpet-like arrays of carbon nanotubes (CNTs) on graphitic carbon materials have been investigated in order to understand all-carbon hierarchical structures for multifunctional surface-active devices. Pure CNT carpets are seen to be super-hydrophobic as long as they are well aligned. For future applications involving aqueous environments, the ability to tailor the surface wettability and switch it on demand can be very useful, and enable unprecedented devices related to microfluidics, catalysis and sensing/ detection systems. In this study, microwave plasma treatments were used to functionalize CNT carpets for a progressive increase in wettability so that they could eventually become super-hydrophilic. This change could be reversed by heating. Alternating between microwave plasma treatment and heating enabled repeated cycling of the CNT carpets between super-hydrophobic and super-hydrophilic states. This paper focuses on the influence of these two treatments on surface chemical states and multiscale morphology of CNT carpets, and their relation to wettability. It was shown by X-ray Photoelectron Spectroscopy (XPS) that oxygen-containing groups attached to surface carbon atoms are created during plasma treatment. These species desorb at temperatures of about 110 C. The strength of C 1s and O 1s XPS signals from these radicals were seen to have direct correlation with water contact angles. In addition to surface chemistry, carpet morphology plays an important role in contact angle variations. Extreme surface roughness caused by high aspect-ratio of nanotubes would strongly accentuate both hydrophobic and hydrophilic behavior compared to flat surfaces. Classical geometric models of liquid droplets on uneven solids have been considered. Topological image analysis combined with intrinsic contact angle on flat graphene is used to predict the contact angle of these carpets, which matches well with experimental results. This analysis further explains why observed contact angles change if the vertical alignment of CNT is disturbed.

High‐Potential Metalless Nanocarbon Foam Supercapacitors Operating in Aqueous Electrolyte

“…The increased O/C ratio, carboxylate and hydroxyl groups result in enhanced hydrophilicity and lowered contact angle . In addition, hierarchical surfaces with high aspect ratio nanostructures lead to the amplification of the hydrophilic characteristics where water drops effectively spread over the surface and infiltrate into the pores, which matches our results that Gra/CNT foam having hierarchical nanostructures exhibits improved hydrophilicity after only 1 h nitric acid treatment.…”

“…The enhancement is ascribed to the p‐type doping effect of the NO 3 − or carboxylic groups, and the reduced contact resistance between CNT fibers . It is noted that carbon‐based materials with I G / I D ≥ 1 can still exhibit hydrophilic features (contact angle ≤ 90°) for graphene films, CNT filters, and CNT carpets . The increased O/C ratio, carboxylate and hydroxyl groups result in enhanced hydrophilicity and lowered contact angle .…”

Experimental and DFT studies of carbon nanotubes covalently functionalized with an imidazole derivative for electrochemical stability and green corrosion inhibition as a barrier layer on the nickel alloy surface in a sulphuric acidic medium

“…4,5-DPM-functionalized CNT showed a wettability angle of about 85 , and epoxy-coated nickel alloy showed a wettability angle of about around 26 . [30][31][32] The surface wettability results were consistent with the results of spectroscopy studies. As listed in Table 2, the epoxy-coated nickel alloy showed a thickness of about 1026 A, which suggested that in this epoxy-coated nickel, only epoxy functional groups were present.…”

Unexpectedly strong hydrophilic character of free-standing thin films from carbon nanotubes

“…The recovery time of was also slower at this humidity by two orders of magnitude as compared with published results 46 . The partial reversal of the effect could be justified by desorption of weakly bonded C–O components, which can improve water affinity of the CNT material 54 .…”