The Regulatory Mechanism Of The Fluid Transport In Micro-and Nano-Scale Channels Based On The Wettability Of Walls

With the rapid development of science and technology in recent years,the miniaturization of novel equipment such as electronic equipment,biosensors,etc.,has gradually become an inevitable tendency in the development of natural science and engineering technology.After the emergence of micro-nano electromechanical system and micro-nano fluidic device,new requirements are put forward for the exploration of relevant fluid theories.The transport property and behavior of fluids at micro-and nano scale exhibit obvious difference with those at macroscale.As one of the basic properties of fluid transportation,the boundary slippage could to some extent reflect the relevant difference,the in-depth study of the regulatory mechanism of slippage near wall interface has important guiding significance and valuable application for the research and design of the micro-nano fluidic devices.Based on theoretical analysis and numerical simulation methods,this paper investigates the influence factors of the interface slippage of the fluid flowing inside nanochannel,and reveals the intrinsic control mechanism and relationship of the slip length which could reflect the transport efficiency with the contact angle.For the theoretical work,based on the molecular kinematics theory(MKT)for fluid flowing,the relation between the slip velocity and the active energy of the fluid on the solid is established through the friction coefficient of the solid-liquid interface on the channel walls,and the slip length can be further calculated using the friction coefficient and the shear viscosity of confined fluid.Then,based on the MKT for droplet sliding and the moving wetting line theory,the ratio of the wetting line velocity to the cosine angle difference between the advancing and receding contact angles is found to be a constant in a certain system,which could be expressed as a function of the walls wettability.Finally,the control relationship among the slip length and contact angles can be constructed.The theoretical model indicates that the influence factors mainly include the wall wettability,the spatial arrangement of atoms in the wall layer,the surface tension of the fluid,the shear viscosity near the channel interface layer and the effective area in the flow direction of the fluid molecules,whose cooperative action leads to the change in the slip length at the micro-and nano-scale channel.Based on molecular dynamics simulations,the static and dynamic states of Lennard-Jones fluid wetting on smooth solid wall and the slippage near solid interface of fluid transporting in nanochannel are investigated.With all the key parameters involved in the theoretical model being calculated,the effect rules of various influence factors on the wall slippage behavior is revealed.The simulation results indicate that the enhancement of the wall wettability always results in a smaller slip length,but when the arrangement of the solid wall atoms changes,there will also be a lager slip length under the condition of strong wettability.For different kinds of fluid,the one with large viscosity has large slip length in the micro-and nano-scale channel.There is a linear correlation between the ratio of the shear viscosity near the fluid boundary layer to its bulk viscosity and the static contact angles,which is always constant for a specific fluid.Finally,the rationality and correctness of the theoretical model constructed above are verified by the numerical simulation results,and a simplified calculation model of slip length is further proposed.In summary,based on the molecular kinematics theory,a theoretical model of slip length characterized by factors such as the wettability of the transmission channel and the arrangement of atomic distribution is established,and the correctness of the model is verified by the molecular dynamic simulations of Lennard-Jones fluid.The research results deepen the realization and understanding of the fluid flowing at micro-and nano-scale,and provide an important scientific basis and theoretical reference for the flow control with channel properties.