Oil-Grafted Track-Assisted Directional Transport of Water Droplets and Submerged Air Bubbles on Solid Surfaces

Abstract

Wettability-tailored tracks are emerging as an efficient approach to collecting and transporting underwater air bubbles as well as water from the mist. However, tailoring the surface wettability by modifying the surface structural features via physiochemical methods to create superhydrophilic−superhydrophobic contrast tracks suffers from long-term durability issues, while the emerging liquid-infused slippery surface has inherent design engineering limitations and issues from infused oil depletion. Herein, we demonstrate that by selective silicone oil grafting onto the glass substrate, it is possible to create a wettability contrast of ∼ 43°. Further, we illustrate the application of such tracks for underwater air bubble capturing and transportation in an aqueous medium with surface tension ranging from 72 to 43.5 mN/m. In addition, the potential of these nonadhesive and adhesive tracks for water collection from the mist is shown and the critical effect of the track dimension and intertrack spacing on the water harvesting rate is investigated in detail. The study illustrates that the nonadhesive nature of the oil-grafted region enables the easy transport of underwater air bubbles as well as water from the flow medium and thus offers an easy and facile approach to creating substrates for underwater air bubble collection and water harvesting.

A surface-engineered contact lens for tear fluid biomolecule sensing

“…F CAH , the contact angle hysteresis force, is measured in terms of advancing ( θ a ) and receding ( θ r ) angles using the expression F CAH = γd (cos θ r − cos θ a ), where γ (72.8 mN m −1 ) and d (2.94 mm for 10 μL) are the surface tension of the liquid and contact line width, respectively. 15 Herein, the hysteresis force for a 10 μL water droplet on the oil-grafted substrate is estimated to be 4.7 μN, whereas the estimated hysteresis force for the pristine surface is found to be 16.4 μN. The oil grafting reduces the contact angle hysteresis force by nearly 3.5 times.…”

“…The change in the contact angle hysteresis confirms oil grafting, similar to our previous report. 15 To investigate the non-adhesive nature of the silicone oil-grafted substrate against a water droplet, the behaviour of a 10 μL water droplet was investigated for different tilt angles. It is observed that the water droplet starts to move downwards for a tilt angle of 40°, beyond which the droplet starts to slide spontaneously at a velocity that is found to increase exponentially with the sliding angle (Fig.…”

“…13,14 The precise control of hydrophobic and hydrophilic properties at the interface through modification of the surfaces via chemical or physical methods has opened a myriad of applications, including water harvesting, microfluidic platforms, and concentration enrichment of analyte molecules for chemical analysis. 15–17 Among these, wettability contrast droplet assay platforms via selective modification of the surface via chemical or physical approaches and by utilizing the wettability or adhesion difference for droplet splitting have been gaining more attention recently. Such platforms offer unique advantages such as consuming less sample volume, facilitating parallel processing, generating more and better-quality data for comparative as well as multiplexed analysis, and having limited space requirements.…”

A Wettability Contrast SERS Droplet Assay for Multiplexed Analyte Detection

“…A nonadhesive quartz surface was fabricated by grafting silicone oil onto the quartz substrate with the aid of oxygen plasma reported in our previous works. , Initially, the quartz slide was cleaned using piranha solution (H 2 SO 4 and H 2 O 2 , 3:1), rinsed with water, and then dried in ambient air. The silicone oil grafting onto the cleaned substrate was carried out by exposing the substrate to oxygen plasma from a commercial oxygen plasma (Femto low-pressure plasma system, Diener electronic) at 90 W for 60 s at a 0.25 mbar pressure.…”