Research progress of slippage characteristic and gas film stability enhancement methods on biomimetic hydrophobic surfaces

The biomimetic hydrophobic surface is a potentially efficient underwater drag reduction method and the drag reduction mechanism of this kind of surface comes from the interfacial slippage.For now,it is a hotspot to grasp the slippage characteristic and explore slippage enhancement strategies.This paper not only summarizes our numerical simulation and experimental results of slippage characteristic at the solid-liquid interface(SLI)of hydrophobic surfaces(HS)and the gas-liquid interface(GLI)of superhydrophobic surfaces(SHS)in recent years,but also introduces some innovative methods that can effectively improve the gas film stability and drag reduction effect of SHS.First,we used the molecular dynamics(MD)simulation method to figure out the effect of the solid-liquid interaction strength,the system temperature and the shear rate on the slippage of SLI,and expound their action mechanism from molecular scale.Then,by MD and multibody dissipative particle dynamics(MDPD)method,the slippage behavior at the GLI was studied under the influence of the microstructure size and the flow driving velocity.We proposed a new kind of hybrid slip boundary condition model to describe the slippage characteristic on GLI.In addition,we found through experiment that a three-dimensional backflow will appear on the GLI under the interfacial adsorption of surfactants,and the backflow direction will reverse with the change of GLI morphology.Finally,we put forward the wettability step structure and gas injection method to enhance the stability and drag reduction effect of the gas film on SHS.

Damping of Magnetorheological Elastomers

The damping property of magnetorheological （MR） elastomers is characterized by a modified dynamic mechanical-magnetic coupled analyzer. The influences of the external magnetic flux density, damping of the matrix, content of iron particles, dynamic strain, and driving frequency on the damping properties of MR elastomers were investigated experimentally. The experimental results indicate that the damping properties of MR elastomers greatly depend on the interfacial slipping between the inner particles and the matrix. Different from general composite materials, the interracial slipping in MR elastomers is affected by the external applied magnetic field.

Roughness Effects on Continuous and Discrete Flows in Superhydrophobic Microchannels

The dynamic behaviors of continuous and discrete flows in superhydrophobic microchannels are investigated with a lattice Boltzmann model.Typical characters of the superhydrophobic phenomenon are well observed from our simulations,including air trapped in the surface microstructures,high contact angles,low contact angle hysteresis,and reduced friction to fluid motions.Increasing the roughness of a hydrophobic surface can produce a large flow rate through the channel due to the trapped air,implying less friction or large apparent slip.The apparent slip length appears to be independent to the channel width and could be considered as a surface property.For a moving droplet,its behavior is affected by the surface roughness from two aspects:the contact angle difference between its two ends and the surface-liquid interfacial friction.As a consequence,the resulting droplet velocity changes with the surface roughness as firstly decreasing and then increasing.Simulation results are also compared with experimental observations and better agreement has been obtained than that from other numerical method.The information from this study could be valuable for microfluidic systems.