Ahesion,Shear And Transport Of The Confined Water At Nanoscale

Water,known as the source of life,holds the pulse of life on earth.In daily life and industrial production practice,water generally exists in the form of bulk water.At the same time,water is subject to the environment,and then forms the confined water with different degrees.In recent years,with the development of nanotechnology and the improvement of cognitive level,people are more and more interested in the research of nanoconfined water.The main reason is that,with people’s production practice and scientific research gradually deepening into the nano scale,the influence of surface/interface force is prominent.There are many differences between bulk and confined water,such as in the field of structure,thermodynamics,dynamics,electronic science and material science,which produce new problems,new phenomena,and need to be studied with a new perspective.In this paper,the size range of the study is controlled in 0.3-100 nm.Based on the different loading forms of nanoconfined water(“strain”,“shear”,“push”),the structure,thermodynamics and kinetic characteristics of nanoconfined water are systematically and deeply studied by theoretical analysis and molecular dynamics simulation methods,so as to explore its influence in the fields of physics,chemistry,biology and energy.The main contents are briefly summarized as follows:(1)the peeling behavior between nanowires and substrates in the ambient condition with high relative humidity is analyzed using continuum modeling under the combined effect of capillary force and vd W force.The capillary force is obtained by solving both the Kelvin equation and the Young-Laplace equation in the thermodynamic equilibrium state,while it is derived by solving both the Young-Laplace equation and the volume equation in the thermodynamic nonequilibrium state.The vd W force is derived from the first derivative of the cohesive energy versus distance.Our analytical results from the modified Kendall model show that the peeling behavior between the nanowire and the substrate strongly depends on the peeling angle,the pre-tension,the radius,the Young’s modulus of the nanowire,the relative position of liquid bridge and the bending stiffness of the nanowire.(2)we develop a refined molecular-kinetic theory(MKT)of the dynamic wetting by considering both liquid-solid and liquid-solid-vapor interfaces.The capillary shearing process of liquid bridges between two graphene films is studied using large-scale molecular dynamics(MD)simulations.Our MD results show that the shear stress at the liquid-solid-vapor interface is the same order of magnitude with that at the liquid-solid interface.Stronger the depth of the Lennard-Jones(LJ)potential between liquid and solid molecules results in smaller static/dynamic contact angles,but larger friction coefficients and interfacial adhesion energies.The total shear stress of three-dimensional(3D)liquid bridges increases with increasing the velocity of the graphene film within a certain range.The sizes of liquid bridges sharply affect the shear stress of liquid bridges,but hardly affect the static/dynamic contact angles.The present refined MKT has higher accuracy than the other available theoretical model with increasing the velocity of graphene films by comparison with MD simulations.(3)nanoconfined water in MGPNs with diameter D ranging from 0.82 to 3.4 nm are investigated by full-atom molecular dynamic simulations,providing key structure and dynamics parameters including density,dipole orientation,diffusion coefficient,friction coefficient and shear viscosity.The confinement effect of MGPNs is fully revealed,which indicate a critical pore diameter(D_c)of 1.36 nm determining internal water structure and dynamics.Confined water in MGPNs with diameter smaller than or equal to D_c exhibit layer structure and abnormal diffusion.For better understanding water dynamics in MGPNs,water flux and flow enhancement factor are characterized.All the calculated structural and dynamics properties of nanoconfined water in MGPNs are also compared with published results obtained from carbon nanotubes with similar sizes,which for the first time unveil the impact of inner wall topology of nanopore on nanoconfined water.