Controllable and switchable capillary adhesion mechanism for bio-adhesive pads: Effect of micro patterns

作     者：ZHANG XiangJun LIU Yuan LIU YongHe AHMED S.I.-U. 

作者机构：State Key Laboratory of Tribology Tsinghua University Beijing 100084 China Institute of Physics and Center for Micro/Nano Technology Technical University of IImenau PF 100565 Germany 

出 版 物：《Chinese Science Bulletin》 (中国科学通报)

年 卷 期：2009年第54卷第10期

页      面：1648-1654页

核心收录：

学科分类：0820[工学-石油与天然气工程] 082903[工学-林产化学加工工程] 08[工学] 0829[工学-林业工程] 082002[工学-油气田开发工程] 

基　　金：Supported by the National Natural Science Foundation of China (Grant Nos. 50575123, 50730007) PPP Project from CSC and DAAD German Research Foundation (DFG) (Grant No. SFB622) (Y.H. Liu and S.I.-U. Ahmed) 

主　　题：毛细管力 可能机制 粘合剂 粘附 生物 开关 可控 玻璃表面 

摘      要：Some insects and animals, such as bugs, grasshoppers and tree frogs, realize their efficient adhesion mechanism to glass surface, wall and ceiling by injecting a wetting liquid thin film into the pad-substrate contact area. Their ability to control adhesion (attaching or detaching from a surface) is in many cases connected to the contact geometry and surface patterns of their attachment pads. This paper focuses on the dependence of the capillary adhesion (wet adhesion) on the micro patterns of the bio-adhesive pads. The objective is to reveal the possible mechanism for a bio-adhesive pad to control capillary force through adjusting its micro-scale surface pattern and topography. A capillary adhesion force model is built up taking account of the combined role of micro-dimple geometry as well as the wetting behavior of the confined liquid thin film. Calculated results of the apparent contact angle on the regularly micro-dimpled surfaces are compared with and in good agreement with the experimental measurements. Simulation of the capillary adhesion force reveals that it is controllable in a large mag- nitude by adjusting a dimensionless surface pattern parameter k defined as a/(a+b), where a is the dia- meter of micro dimple, and (a+b) is the side length of one pattern cell. When adjusting the parameter k more than 0.75, the capillary adhesion force could be switchable from attractive to repulsive. This effect of micro patterns on the interfacial capillary force is proved to be dominant when the pad-substrate clearance decreases to the nano/micrometer scale. These results indicate that a controllable and switchable capillary adhesive mechanism might be utilized by a living insect or animal to realize its stable adhesion and quick releasing movement through adjusting the micro-pattern topography of its bio-adhesive pad.