Understanding the wetting behaviors of droplets on grooved surfaces is indispensable in surface science and offers promising avenues for advancing industrial processes. The droplet spreading on grooved surfaces can be discretized into a series of individual events that the droplet across each groove with variations in capillary forces and a subsequent re-equilibrium. In this work, a simplified model of droplet spreading on surface with an individual groove on both the left and right sides was utilized in order to elucidate the fundamental mechanisms underlying contact line pinning due to the groove. We examined the effects of the groove position and the wettability of solid surfaces. The contact line is observed to be pinned when the grooves are strategically positioned. However, by reducing the distance between the grooves, the contact lines can cross them. In such instances, the spreading process can be classified into four modes: Free spreading, impeding spreading, pinning, and depinning. The pinning and depinning phenomenon are explained by the balance between the driving force and pinning force on the contact line. Based on simulation results, the maximum pinning force exerted on the contact line by a certain solid surface can be theoretically predicted. Besides, the wettability of the solid surface also contributes to the impeding effect. This work provides theoretical guidance for the study of wetting on grooved surfaces at the nanoscale, which is essential for developing a comprehensive understanding of the interactions between droplets and structured surfaces, with potential applications in optimizing industrial processes and advancing surface science.

Interactions at the oil/brine/rock interfaces play a pivotal role in the mobility of crude oil within reservoir matrices. Unraveling the microscopic mechanisms of these interactions is crucial for ion-engineered water flooding in secondary and tertiary oil recovery. In this study, the occurrence and transport behavior of crude oil in kaolinite nanopores covered with thin brine films was investigated by molecular dynamics simulation. There is an apparent interface layered phenomenon for the liquid molecules in slit pores and the polar oil components primarily concentrate at the oil/brine interfacial region and form various binding connections with ions. The interfacial interactions between the polar oil components and brine ions exhibit an inhibitory effect on the transport of crude oil through nanopores. The interaction mechanism between acetic acid molecules and hydrated ions was elucidated by interaction modes and interaction intensity, which was proved to illustrate the flow difference in different brine film systems. Moreover, a strategy of exchanging the binding sites of divalent cations with acetic acid molecules by monovalent cations with a higher concentration was proposed. The cation exchange scheme was further validated, demonstrating an enhancement in the oil mobility within nanopores. These findings deepen our understanding of oil/brine/rock interfacial interactions and provide a significant molecular perspective on ion-engineered water flooding for enhanced oil recovery.

The quest for widespread applications especially in extreme environments accentuates the necessity to design materials with robust mechanical and thermodynamic stabilities. Almost all existing materials yield temperature-variant mechanical properties, essentially determined by their different atomic bonding regimes. In general, weak non-covalent interactions are considered to diminish the structural anti-destabilization of covalent crystals despite the toughening effect. Whereas, starting from multiscale theoretical modeling, we herein reveal an anomalous stabilizing effect in cellulose nanocrystals (CNCs) by the cooperation between the non-covalent hydrogen bonds and covalent glucosidic skeleton, namely molecular levers (MLs). It is surprising to find that the hydrogen bonds in MLs behave like covalent bindings under cryogenic conditions, which provide anomalously enhanced strength and toughness for CNCs. Thermodynamic analyses demonstrate that the unique dynamical mechanical behaviors from ambient to deep cryogenic temperatures are synergetic results of the intrinsic temperature dependence veiled in MLs and the overall thermo-induced CNC destabilization/amorphization. As the consequence, the variation trend of mechanical strength exhibits a bilinear temperature dependence with ~ 77 K as the turning point. Our underlying investigations not only establish the bottom–up interrelations from the hydrogen bonding thermodynamics to the crystal-scale mechanical properties, but also facilitate the potential application of cellulose-based materials at extremely low temperatures such as those in outer space.

Understanding molecular interactions between oil and reservoir matrix is crucial to develop a productive strategy for enhanced oil recovery. Molecular dynamics simulation has become an important method for analyzing microscopic mechanisms of some static properties and dynamic processes. However, molecular modeling of shale oil and reservoir matrix is still challenging, due to their complex features. Wettability, which is the measurement of oil-matrix interactions, requires in-depth understanding from the microscopic perspective. In this study, the density, interfacial tension and viscosity of eleven common components in shale oil are calculated using molecular dynamics simulations. Then a molecular model of Gulong shale oil is built, based on the reported experimental results and simulations. Compared with the variation in hydrocarbon content, the change in polar component content leads to more significant variations in the physical properties of shale oil. This molecular model is also employed to investigate the wettability of shale-oil nanodroplets on minerals and organic matter, with or without the surrounding aqueous phase. This work suggests fresh ideas for studying the oil-matrix interactions on the nanoscale and provides theoretical guidance for shale oil exploitation.