Fabrication Of Superhydrophobic Micro Post Array With Controllable Structure And Wettability Using Mask Electrochemical Machining

Superhydrophobic surfaces have become a research focus owing to their various applications in self-cleaning,corrosion resistance,anti-icing and oil-water separation.Comparing with superhydrophobic surfaces of disordered micro structures,superhydrophobic micro post arrays that have controllable parameters appear to be more effective in revealing the mechanisms of superhydrophobicity,such as: the variation three phase contact line during evaporation or endowing special functions.But existing methods are always inefficiency and have difficulty in fabricating superhydrophobic micro post array of large area on metal substrates.Facing on these,in this paper,a facile method of mask electrochemical machining was proposed to fabricate superhydrophobic micro post arrays with controllable structures on aluminum substrates.And the mechanism of this proposed method was further studied through both simulation and experiment to investigate how to control the array structure and wettability by adjusting the machining parameters.The main conclusions are as follows:(1)A model for the simulation of mask electrochemical machining process was built using ANSYS platform.Interaction of the structure changes during the machining and the electric field distribution was analyzed.And the law of array structure changes with machining current density and time during the mask electrochemical machining process was obtained by the iterative calculation of arbitrary nodes on the contact line of electrolyte and aluminum plate.(2)According to the results of simulation,a polynomial fitting was carried out to establish the variation law of diameter and height of the micro post with the electrochemical machining parameters.The fitting results can be used to predict anticipate parameters of arrays and fabricate superhydrophobic micro post array controllable structure.(3)Experiments of fabrication of superhydrophobic micro post arrays on aluminum substrates were conducted.And the accuracy of the simulation was verified by comparing the experimental results to the simulation results.The obtain micro array structures were then immersed in fluoroalkylsilane-ethanol solution to lower surface energy,and superhydrophobic surfaces with a maximum contact angle of 162.3° were obtained.(4)Through the observation and analyze of solid-liquid-gas three phase contact situation when a water droplet was displaced on the array structures as-prepared,the superhydrophobic micro post arrays prepared by mask electrochemical machining were found in a contact mode of Cassie-Baxter,while the un-superhydrophobic post arrays were in a contact mode of Wenzel.Analyze of microcosmic force was conducted to investigate the reason of this contact mode difference.(5)According to the Cassie-Baxter theoretical model,investigation of the relationship between solid fraction of and the contact angle of the post array was carried out.The results showed that the apparent water contact angle of the micro post arrays fabricated through mask electrochemical machining was in accordance with the theoretical value computed by Cassie and Baxter.Thus,basing on the relationship between machining parameters and array structure and the relationship of array structure and water contact angle,superhydrophbic micro post arrays with both controllable structure and wettability can be fabricated using mask electrochemical machining.