Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper,the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness p...Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper,the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness parameters are investigated.Atheoretical model is proposed to study wetting transitions.The results of theoretical analysis are compared with those of experimentindicating that the proposed model can effectively predict the wetting transition.Furthermore,a numerical simulationbased on the meso scale Lattice Boltzmann Method(LBM)is performed to study dynamic contact angles,contact lines,andlocal velocity fields for the case that a droplet displays on the micro structured surface.A spherical water droplet with r=15μmfalls down to a biomimetic square-post patterned surface under the force of gravity with an initial velocity of 0.01 m·sand aninitial vertical distance of 20μm from droplet centre to the top of pots.In spite of a higher initial velocity,the droplet can stillstay in a Cassie state;moreover,it reaches an equilibrium state at t≈17.5 ms,when contact angle is 153.16°which is slightlylower than the prediction of Cassie-Baxter’s equation which givesθ=154.40°.展开更多
The concept of electroosmotically driven flow is built around understanding how the ionized particles or fluid are driven to flow by electroosmosis forces. Apart from the major applications of this concept to micro f...The concept of electroosmotically driven flow is built around understanding how the ionized particles or fluid are driven to flow by electroosmosis forces. Apart from the major applications of this concept to micro flow control elements which have been explored in parallel with the rapid developments in micro fabrication technologies, the present focus is on its application to biomimetics. As soil animals (in fact all living creatures) such as earthworms and dung beetles carry bioelectricity, the relative movement between the creatures and the surrounding soil which is a multi-component medium with moist content will generate electrophoresis or electroosmosis forces. Such forces drive the ionized moist content, normally water, to migrate from positive to negative poles under the action of electric double layer (EDL) effect, and effectively reduce the adhesion or drag.Predicting the electroosmotically driven flow in the vicinity of biological and animal surfaces is a key problem of drag/adhesion reduction and biomimetics design. The aim of this article is to demonstrate how the theory of electroosmotically driven flow has developed and to describe its broader significance for anti adhesion of soil animals and biomimetics design of soil machinery tools.展开更多
Fingering phenomena are common occurrence in the natural world.It generally takes place when a less viscous fluid displacesa more viscous fluid typically in porous media.Nowadays,such phenomena have extensively been s...Fingering phenomena are common occurrence in the natural world.It generally takes place when a less viscous fluid displacesa more viscous fluid typically in porous media.Nowadays,such phenomena have extensively been studied due to itsimportance in many industrial fields.In this paper,the effects of surface wettability on finger pattern are studied and simulatednumerically by the Lattice Boltzmann method(LBM).The displacement efficiency is investigated by using two parameters,namely,the breakthrough time and the areal sweep efficiency.The simulation has demonstrated that surface wettability willinfluence the finger pattern no matter the gravity is considered or not,but in the presence of gravity,the finger pattern is muchmore complicated and irregular due to the coexistence and competition of capillary force,viscous force and gravity.展开更多
基金supported by the Royal Society(UK)-NSFC(China)joint project,2009-2011by China Natural Science Foundation major International collaborative project 2010-2013 under grant No.50920105504
文摘Natural surfaces with super hydrophobic properties often have micro or hierarchical structures.In this paper,the wettingbehaviours of a single droplet on biomimetic micro structured surfaces with different roughness parameters are investigated.Atheoretical model is proposed to study wetting transitions.The results of theoretical analysis are compared with those of experimentindicating that the proposed model can effectively predict the wetting transition.Furthermore,a numerical simulationbased on the meso scale Lattice Boltzmann Method(LBM)is performed to study dynamic contact angles,contact lines,andlocal velocity fields for the case that a droplet displays on the micro structured surface.A spherical water droplet with r=15μmfalls down to a biomimetic square-post patterned surface under the force of gravity with an initial velocity of 0.01 m·sand aninitial vertical distance of 20μm from droplet centre to the top of pots.In spite of a higher initial velocity,the droplet can stillstay in a Cassie state;moreover,it reaches an equilibrium state at t≈17.5 ms,when contact angle is 153.16°which is slightlylower than the prediction of Cassie-Baxter’s equation which givesθ=154.40°.
文摘The concept of electroosmotically driven flow is built around understanding how the ionized particles or fluid are driven to flow by electroosmosis forces. Apart from the major applications of this concept to micro flow control elements which have been explored in parallel with the rapid developments in micro fabrication technologies, the present focus is on its application to biomimetics. As soil animals (in fact all living creatures) such as earthworms and dung beetles carry bioelectricity, the relative movement between the creatures and the surrounding soil which is a multi-component medium with moist content will generate electrophoresis or electroosmosis forces. Such forces drive the ionized moist content, normally water, to migrate from positive to negative poles under the action of electric double layer (EDL) effect, and effectively reduce the adhesion or drag.Predicting the electroosmotically driven flow in the vicinity of biological and animal surfaces is a key problem of drag/adhesion reduction and biomimetics design. The aim of this article is to demonstrate how the theory of electroosmotically driven flow has developed and to describe its broader significance for anti adhesion of soil animals and biomimetics design of soil machinery tools.
基金supported by the NSFC sponsored project under grant(50976017)(50736001)
文摘Fingering phenomena are common occurrence in the natural world.It generally takes place when a less viscous fluid displacesa more viscous fluid typically in porous media.Nowadays,such phenomena have extensively been studied due to itsimportance in many industrial fields.In this paper,the effects of surface wettability on finger pattern are studied and simulatednumerically by the Lattice Boltzmann method(LBM).The displacement efficiency is investigated by using two parameters,namely,the breakthrough time and the areal sweep efficiency.The simulation has demonstrated that surface wettability willinfluence the finger pattern no matter the gravity is considered or not,but in the presence of gravity,the finger pattern is muchmore complicated and irregular due to the coexistence and competition of capillary force,viscous force and gravity.
