Study On Mechanical Control Of Wettability On Soft Hierarchical Wrinkling Structured Surface

In our daily life,surface instability often occurs which is caused by the difference of surface and internal elastic properties,such as the skin of the melon,wrinkles,etc.In recent years,with the development of biomimetic technology,it has been possible to manually control the size of the flexible wrinkling structures,which has attracted the attention of researchers.In this paper,from the perspective of thermodynamics,the wetting states and wetting stability of primary and multilevel wrinking structures are analyzed.And the effectiveness of theory results is verified by the experimental results.Then the wrinkling structure is combined with the wetting gradient to realize the directional movement of droplet and more intelligent control the spread length in the same time by the structure design.The main research results and innovations are as follows:(1)The contact angle equation of two wetting states of droplet on wrinkling structures surface are deduced.The transition process of droplet on wrinkling strutures surface and the trend of the potential barrier are analyzed in detail.The relationship of prestrain and apparent contact angle is established through the theoretical prediction formula between the size of wrinkling structure and the prestrain.The wrinkling structures are prepared by mechanical stretching and the experimental results are in a good agreement with the theoretical calculations.Finally,the intelligent control of surface wettability of wrinkling structures are achieved by in-situ mechanical loading.(2)The wetting states of droplet on the surface of hierarchical wrinkling structures are studied.And the contact angle equation of every wetting states is derived.The influences of strips and wrinkling structures size on wetting states are analyzed detailed.Then the change of free energy and the energy barrier of wetting transition process is analyzed.Finally,through the experimental preparation of hierarchical wrinkling structures,the theoretical calculation is verified and is in a good agreement with the experiment results.(3)The anisotropic wettability of wrinkling structures is used to improve the droplet flow length.The chemical wetting gradient is prepared by plasma etching in the direction of parallel to the wrinkling structures.The spread of droplet can be changed in the same wetting gradient by control the size of wrinkling structures,because of the flexible characteristic of the wrinkling structures.(4)The directional spreading of droplet on wrinkling structures surface which has chemical and structure wetting gradient is analyzed.The contact angle range of droplet on the hydrophobic surface of structure wetting gradient is small.On the surface of chemical gradient,its range is only from hydrophobic to hydrophilic or hydrophobic to super hydrophilic.Combining the structure and chemical wetting gradient,the range of contact angle is further increase and the spreading effect of droplet can be improved.In summary,hierarchical structures have an important influence on surface wettability.The relationship of wettability and wrinkling structure is established.And the mechanical control of wettability on wrinkling structures surface is realized.The length of droplet directional spreading is improved and intelligently controlled by combining the wrinkling structures and wetting gradient.