Dynamic Behaviors Of Condensed Microdrop And Impacting Droplet Of Bionic Nanostructured Polypropylene Surfaces

The interaction of droplets and solid surfaces is a common phenomenon.Inspired by the micro-nano structure of biological surfaces in nature,it is of great significance to design a super-hydrophobic surface with high-efficiency condensed microdrop self-propelled(CMDSP)function.Referring to the nano-pillar structure on the cicada wing surfaces,this dissertation uses anodized aluminum(AAO)as templates to fabricate polypropylene(PP)replicas by injection compression molding(ICM)and characterizes the CMDSP behavior and the water droplet impact behavior on PP replica surfaces.Using the AAO-500~#template as the mold insert,the PP-500~#replica with efficient and fast CMDSP function is prepared by ICM technology.The replica surface has a small energy ratio in the wet state(E~*?0.43)and an ultra-low solid-liquid contact area fraction(?_s?0.025),indicating that the nanopore structures of the AAO-500~#template is well replicated onto it.Obvious microdrop jumping and microdrop sweeping behavior can be observed on the surface.The diameter of the condensed microdrops is mostly below 20?m,and the self-propelled behavior can easily occur when the average microdrop diameter is about 15?m.The energy change during droplet jumping is analyzed in detail,and the bounce velocity generated by the combination of two droplets is derived using the formula.Shortly after the condensation test starts(18 s),the sweeping behavior triggered by several microdrops coalescence can be observed,and then the sweeping distance will become longer and longer(>1 mm),and self-propelled sweeping phenomena in different directions will occur.The effects of structure size parameters on CMDSP phenomena are studied by forming PP replicas with different height nanocone structures.As the height of the tapered nanostructure increases,the higher the self-propelled frequency of condensed microdrops on the replica surfaces,the longer the sweeping distance and the stronger the ability to update the surface microdrops.To explore the water droplets impact robustness on PP-500~#replica under different conditions.The contact time of impacting water droplet has little relation with the change of We number.The loss of energy of the water droplet upon impact can be represented by coefficient of restitution(?),and the water droplets splashing under high We would cause more energy loss.When impacting the PP-500~#replicas surfaces with different inclination angles,the water droplets will slip while expanding,and the slip displacement is quantitatively characterized.The effects of different height nanocone structures on the water droplet impact behavior on PP-500~#replicas are investigated.The anti-freezing adhesive characteristics of the nanostructured surface are analyzed from both static and dynamic aspects.The PP-500~#replica greatly extend the freezing time of 7?L water droplets on its surface,which is 5.4 times that of the smooth PP counterpart.The impact water droplets can still maintain good dynamic superhydrophobic stability at the low temperature(0?and-10?)PP-500~# replica surface.