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• Transmission of molecular interactions through graphene can drive migration of droplets. • Enhancing electric field accelerates migration velocity of two droplets towards each other. • Dipole–dipole interactions of interfacial water enhance deflection of water dipoles. • Critical electric field to induce large deformation becomes lower for cases of two droplets. Understanding the physical mechanism of wetting transparency of monolayer graphene, or how atoms or molecules located on opposite sides of the atomically thin carbon monolayer transmit molecular interactions (such as van der Waals and electrostatic forces) is of significant importance for many extraordinary applications from scientific and practical perspectives. In the current work, we carried out molecular dynamics simulations to explore the interactions between two droplets (TD) separated by the monolayer graphene under applied electric field. The results indicate that in the absence of the electric field the transmission of molecular interactions can drive migration of two droplets towards each other, implying partial wetting transparency of the graphene. Compared to the cases of single droplet (SD), the critical electric field to induce large deformation is lower for the TD cases. However, the droplet–droplet interactions under strong electric fields suppress the reduction of the number of water molecules in the graphene/droplet interface and the elongation of droplets. To understand the enhancement of interactions between two droplets owing to the electric field, we analyze microscopic structures of interfacial water (dipole orientation distribution and hydrogen bonding). The dipole–dipole interaction through the graphene mainly contributes to the droplet–droplet interactions. It was found that significant deflection of water dipoles for the TD cases occurs as the electric field enhances, but the deflection for the SD cases is smaller and even the droplet is detached from the graphene surface. Our findings provide fundamental insights on the influence of the electric field on molecular interactions between two droplets through the monolayer graphene and clues for developing potential graphene-based nanofluidic applications controlled by external electric field. [ABSTRACT FROM AUTHOR]

The presence of water molecules can significantly determine the macroscopic mechanical property and microscopic chain dynamics of poly(vinyl alcohol) (PVA). However, to date it has remained fully understood the molecular mechanism behind experimentally and theoretically. Herein, we systematically examine the effect of water contents on the mechanical property, glass transition, free volume, and intermolecular interactions by combining experimental and MD simulation. Our results show that the presence of water significantly reduces the mechanical strength of PVA, and only 1.8 wt% of water reduces the tensile strength by ~32% but notably increases the plasticity of PVA by ~2.5 times. Meanwhile, the inclusion of water remarkably lowers the glass transition temperature, increases free volume, and promotes the relaxation and mobility of PVA chains. This is mainly because the presence of water gives rise to both the plasticization and even lubricating effect on the PVA chains. This work unravels how water governs the mechanical performances of the PVA. Image 1 • The presence of water significantly reduces the mechanical strength of PVA. • 1.8 wt% of water reduces tensile strength by ~32% but increases the ductility of PVA by ~2.5 times. • The inclusion of water remarkably lowers the glass transition temperature of PVA. • The addition of water increases the free volume and promotes the relaxation of PVA chains. • The presence of water giving rise to the plasticization and lubricating effect on the PVA chains. [ABSTRACT FROM AUTHOR]