Solid-like Behaviors Govern Evaporative Transport in Adsorbed Water Nanofilms

Recent Progress on Liquid Superspreading and Its Applications

The dynamic spreading of liquids on solid surfaces is essential across numerous daily and industrial processes. Surfaces that enable liquid superspreading, characterized by rapid or extensive spreading, are particularly valuable due to their implications in functional film fabrication, heat management, liquid/liquid separation, and more. Recently, significant research is conducted on liquid superspreading surfaces, with microstructure-regulated surfaces gaining increasing attention. However, the deeper correlations between microstructural physical factors and the superspreading behaviors, along with the relevant applications, remain inadequately understood. This review aims to consolidate the existing knowledge from published results and stimulate further investigation by detailing structures, functionalities, and principles for constructing liquid superspreading surfaces. Examining is began by the energy balance between input and dissipation that underpins droplet spreading dynamics. Then current designs are reviewed for superspreading surfaces, with a focus on chemical and physical aspects, giving greater emphasis to the physical perspective. Additionally, several typical applications are categorized based on liquid superspreading behaviors across various fields. Finally, the prevailing challenges are highlighted and provide insights into future research directions.

Speleothem-Inspired Copper/Nickel Interfaces for Enhanced Liquid-Vapor Transport by Marangoni and Soret Effects

Geological formations have superior wickability and support the absorption of water and oils into narrow spaces of Earth's crust without external assistance. In this study, we present speleothem inspired heterogeneous porous and wicked copper (Cu)/nickel (Ni) interfaces for enhanced nucleate boiling of water/ethanol mixtures for energy-efficient separation processes. The incorporation of Ni strands within the copper particle matrix significantly enhanced heat transfer. Compared to plain copper, the Cu/Ni speleothem surfaces exhibited a 61% increase in the heat transfer coefficient for water/ethanol mixtures and a 332% increase for water, with a 58% faster onset of nucleate boiling. This enhancement was attributed to Marangoni and Soret effects at the Cu/Ni interfaces, driven by surface tension and concentration gradients. Furthermore, the synergistic wicking action of the Ni strands facilitated rewetting of the surface, replenishing liquid to the porous nucleation sites and preventing surface dry-out, thereby improving the overall heat transfer performance.

Interfacial Features Govern Nanoscale Jumping Droplets

The solid surfaces with different profile levels impact the liquid-solid contact nature and hence wetting characteristics, showing a vital role in liquid droplets' mobility and dynamic behaviors. Therefore, engineering nanostructured features ultimately enables tuning and controlling the dynamic motion of droplets. In this study, we demonstrate an approach to manipulate nanodroplets' motion behaviors in contact with a surface through tailoring the surface morphological profile. By tracking the trajectories of water molecules at the interface, we find that the motions of a nanodroplet subjected to different levels of lateral force reveal various modes that are identified as creeping, rolling, and jumping motions. Interestingly, the elastic deformation of the droplet and sudden changes in the receding contact angle provide the mechanistic origin for droplet jumping. Guided by computational simulations, a regime map delineating the droplet motion modes with surface profile levels and applied forces is constructed, providing a design strategy for controlling droplet motions via surface engineering.

Evaporation of Water Nanodroplets on Heated Surfaces: Does Nano Matter?

While experiments and continuum models have provided a relatively good understanding of the evaporation of macroscopic water droplets, elucidating how sessile nanodroplets evaporate is an open question critical for advancing nanotechnological applications where nanodroplets can play an essential role. Here, using molecular dynamics simulations, we find that evaporating nanodroplets, in contrast to their macroscopic counterparts, are not always in thermal equilibrium with the substrate and that the vapor concentration on the nanodroplet surface does not reach a steady state. As a result, the evaporative behavior of nanodroplets is significantly different. Regardless of hydrophobicity, nanodroplets do not follow conventional evaporation modes but instead exhibit dynamic wetting behavior characterized by huge, non-equilibrium, isovolumetric fluctuations in the contact angle and contact radius. For hydrophilic nanodroplets, the evaporation rate, controlled by the vapor concentration, decays exponentially over time. Hydrophobic nanodroplets follow stretched exponential kinetics arising from the slower thermalization with the substrate. The evaporative half-lifetime of the nanodroplets is directly related to the thermalization time scale and therefore increases monotonically with the hydrophobicity of the substrate. Finally, the evaporative flux profile along the nanodroplet surface is highly nonuniform but does not diverge at the contact line as the macroscopic continuum models predict.

Achieving the Super Gas-Wetting Alteration by Functionalized Nano-Silica for Improving Fluid Flowing Capacity in Gas Condensate Reservoirs

It is well-known that the production of gas-condensate reservoirs is significantly affected by the liquid condensation near the wellbore region. Gas-wetting alteration can be one of the most effective approaches to alleviate condensate accumulation and improve liquid distribution. However, gas well deliverability is still limited because the wettability of cores is altered only from liquid-wetting to intermediate gas-wetting by using traditional chemical stimulation. To solve this bottleneck problem, herein, we developed a fluorine-functionalized nanosilica to achieve super gas-wetting alteration, increasing the contact angles of water and n-hexadecane on the treated core surface from 23 and 0° to 157 and 145°, respectively. The surface free energy reduces rapidly from 67.97 to 0.23 mN/m. The super gas-wetting adsorption layer on the core surface formed by functionalized nanosilica not only increases the surface roughness but also reduces the surface free energy. The core flooding confirms that the required pressure for displacement is apparently reduced. Meanwhile, the core permeability can be dramatically restored after the super gas-wetting alteration. The microscopic visualization is employed to further understand the impact of fluorine-functionalized nanosilica on the fluid flow behavior and mechanism in porous media. The oil saturation in the micromodel decreases sharply from 48.75 to 7.84%, eliminating the "water locking effect" and "Jiamin effect", which indicates that the added functional nanosilica effectively improves fluid flow capacity and may contribute to production in the gas condensate reservoirs. In addition, this work reveals the fluid flow behavior and mechanism in the reservoir in detail, which will expand the better application of this material to many oilfields and other mining engineering systems.