Tunable Surface Wettability via Terahertz Electrowave Controlled Vicinal Subnanoscale Water Layer

Achieving timely, reversible, and long-range remote tunability over surface wettability is highly demanded across diverse fields, including nanofluidic systems, drug delivery, and heterogeneous catalysis. Herein, using molecular dynamic simulations, we show, for the first time, a theoretical design of electrowetting to achieve remotely controllable surface wettability via using a terahertz wave. The key idea driving the design is the unique terahertz collective vibration identified in the vicinal subnanoscale water layer, which is absent in bulk water, enabling efficient energy transfer from the terahertz wave to the rotational motion of the vicinal subnanoscale water layer. Consequently, a frequency-specific alternating terahertz electric field near the critical strength can significantly affect the local hydrogen-bonding network of the contact water layer on the solid surface, thereby achieving tunable surface wettability.

Unraveling the synergistic effects of solid surface material and temperature on the contact angle of water under an elevated pressure: An experimental study

HYPOTHESIS

In terms of the Young's equation, the temperature dependence of liquid-solid contact angle is affected by the surface material, so the wetting behavior could be tuned by both changing the temperature and surface material. However, the synergistic effects of surface material and temperature on the water contact angle remain unclear, especially at elevated temperatures.

EXPERIMENTS

In this study, a systematic characterization of water contact angle against various smooth metallic and nonmetallic surfaces was conducted for temperatures up to 300 ℃ in a high-pressure chamber at 15 MPa. The measured results were finally compared with the predictions made by the sharp-kink approximation model.

FINDINGS

Not surprisingly, it was observed the temperature-dependent water contact angle is sensitive to the type of solid surface. The temperature coefficients and critical temperature points on the contact-angle-temperature curves can be manipulated by altering the surface material. However, the influence of surface material is weakened by raising temperature, thus leading to the nearly consistent temperature-dependent water contact angle over 120℃. Additionally, the necessity of investigating the internal flows within the water drops was highlighted to unravel the positive temperature correlation of the water contact angle at high temperatures, in view of the presence of non-spherical-cap-shaped drops.

Dependency of the structure of a water layer sandwiched by silicon carbide on shear speed and temperature

As a third-generation semiconductor, silicon carbide power devices are expected to be superior to those made of silicon because of their high voltage resistance, low loss, and high efficiency. So understanding the technology for polishing wafers of silicon carbide is important, which includes studying the structure of the liquid on the surface of silicon carbide. Using molecular dynamics based on Lennard-Jones field, the structure of a water film contained within two silicon carbide (〈001〉 and 〈110〉) walls was analyzed, and found that layers of water appear and change depending on the distance between the two walls. When a double-layer water structure forms, it is affected by the temperature and shear velocity. The conclusion is that when the temperature increases or the shear velocity increases, the double-layer water structure easily transforms into a single-layer water structure, and the pressure between the two solid surfaces gradually falls and may even become negative. This phenomenon significantly depends on the distance between the two silicon carbide walls.

Water wettability of graphene: interplay between the interfacial water structure and the electronic structure

Wettability of graphene is characterized from first principles.

Hexagonal SiC with spatially separated active sites on polar and nonpolar facets achieving enhanced hydrogen production from photocatalytic water reduction

The spatial separation of the photo-generated electrons and holes between the polar Si-{0001} and non-polar {10−10} crystal facets on 6H-SiC highly improves the photocatalytic activity of water splitting by nearly 5 times.