Design And Water Droplet Impacting Performance Of Superhydrophobic Micro-/nano-structured Surfaces Prepared By Microinjection Compression Molding

The fine micro-/nano structures presenting on the surfaces of natural organisms endow the surfaces a special wetting behavior and optical behavior.Nowadays,the preparation of replicas with biomimetic surface as template,however,is still insufficient in terms of accuracy,lowcost and high-efficiency.Micro-injection compression molding(?-ICM)is a technology that combines the high-precision of micro-injection molding with the high-precision of microembossing,which plays an increasingly important role in the fileds of preparing micro-/nano structured products.Therefore,?-ICM is an ideal approach to fabricate biomimetic surfaces with precision and fine structures.In this dissertation,the droplet impact robustnesses of the three kind of biological surface with different structures are investigated.Then,the structure of the biological surface(upper surface of lotus leaf)is replicated onto polypropylene(PP)surface by ?-ICM technology,and the wetting behavior and dynamic droplet impact performance of the upper surface of lotus leaf are achieved on the PP replica.On this basis,superhydrophobic surface with milli-/nano structure is prepared by ?-ICM.The droplet impact robustnesses of the superhydrophobic low-adhesion biological surfaces(the upper and lower surfaces of the lotus leaf,the cicada wing surface)are investigated.The upper surface of lotus leaf and the cicada wing surface maintain robust superhydrophobic state at a dynamic pressure of 2940 Pa.Through theoretical calculations,the micro-/nano structured hierarchal lotus leaf(upper surface)can withstand a higher dynamic pressure than the nanostructured cicada wing surface.Single factor test design is designed to investigate the effect of mold temperature,melt temperature,mold compression force and mold compression speed,on the water droplet contact angle(CA)of the polypropylene(PP)replica surfaces.The results show that the mold temperature,melt temperature,and mold compression force have a significant effect on CA.On this basis,the influence of mold temperature,melt temperature and mold compression force on the CA of the PP replicas is investigated by a response surface experiment.The results show that the mold temperature is the most significant processing parameter that influences the CA of the surface,and the melt temperature has a greater impact than the mold compression force.The interaction between the mold temperature and mold compression force is significant.There are certain interactions between mold temperature and melt temperature,melt temperature and mold compression force.Using the upper surface of lotus leaf as template,its hierarchal micro-/nano structure is accurately replicated onto the nickel replica by combining electroless plating and electroplating.The nickel template can be reused at least 70 times.The nanohairs with sharp tips and high aspect ratio are developed on the micro papillae and base surface of the PP replica in the ?-ICM process,thanks to the nanogrooves in the nickel replica.The PP replica exhibits superhydrophobic and non-sticking properties(a CA of ~157° and roll off angle of < 5° for a 4 ?L droplet),self-cleaning behavior and static superhydrophobic stability,which is similar to the surface of the lotus leaf(upper surface).It also can be applied to droplet transfer and reduce the reflection of light with wavelengths from 400 nm to 1300 nm.The PP replica shows an excellent dynamic superhydrophobic robustness and can maintain the Cassie-Baxter state at a dynamic pressure of 1960 Pa.PP replicas with cicada wing-like nanopillars on its surface are prepared by ?-ICM process using two different depths of nanopores of aluminum oxide as templates.The PP replicas show a superhydrophobic and low-adhesion properities,and also exhibit good droplet impact robustness.On this basis,combining aluminum oxide template with grooved stainless-steel plate,PP replicas with milli-/nano structure are prepared by applying ?-ICM technology.In the process of droplet impacting with a Weber number of 108,the contact time of the droplet on the milli-/nano structure surface is reduced by 54.5% compared to the nanostructure surface.