The Hydrophobic Antifogging Mechanism Of Micro-scale Biological Surface And Bionic Design And Manufacture

Fogging phenomenon refers to a certain amount of water vapor condensate on asubstrate surface forming many tiny water drops when temperature drops to below dew point.These drops alter light-scattering, refraction and reflection, affecting of light transmittanceof transparent substrate surface. On the other hand, the substrate will therefore become wet,causing corrosion and other secondary problems. Antifogging problem may be effectivelyaddressed by changing the affinity of a material’s surface for water, which can beaccomplished via two approaches: the superhydrophilic approach and the superhydrophobicapproach. However, the hydrophilic antifogging method can’t change the "wet" nature.Therefore, the hydrophobic antifogging method gradually draws more attention.Nature has always been an important source of engineering innovation. The existingfunction and the structure maintains the best matching experienced millions of years ofevolution. Learning from nature is a shortcut to solve some engineering problems. In thispaper, typical biologies in water, foggy environment were collected, and then Ephemerapictiventris mcLachlan compound eyes and Water bamboo leaves were selected as biologicalprototypes. Then their morphology, structure, wettability and antifogging properties werestudied. Based on establishing the bionic model, hydrophobic antifogging mechanism wasexplained. Bionic structure surfaces were prepared by Laser interference lithography method,Soft lithography method and Colloidal lithography method. Then the morphology andstructure were characterized and the wetting property and antifogging property were tested.It provides the new ideas and methods to design and fabricated hydrophobic antifoggingmaterials.In chapter1, the significance of hydrophobic antifogging research, the main antifoggingstrategies were introduced. Then the progress in hydrophobic antifogging coating technology and structure antifogging technology were summarized. And the progress in naturalsuperhydrophobic surfaces and the effects of different rough forms on hydrophobicperformance were also discussed.In chapter2, the study focus was put on the compound eyes of insects and plant leavesin the water, wet, foggy environment, including mayflies, leafhoppers, water strider anddamselfly etc. Reed leaves, bamboo leaves, water bamboo leaves and lotus leaves were alsoinvestigated. The result shown that the compound eyes of Ephemera pictiventris mcLachlanliving in foggy environment in Sichuan Province exhibit striking hydrophobic antifoggingproperty. The eyes maintained dry, clear state without water film on surface of compoundeyes after blowing fog10minutes continuously. Water bamboo leaf surface growing in freshwater in Zhejiang province behaves excellent superhydrophobic property and someantifogging function, with the static CA value and SA value of151±3deg and about5deg，respectively.In chapter3, the morphology and structure of typical biological compound eye surfacesand plant leaf surfaces were characterizated in detail by stereo microscope, scanning electronmicroscope (SEM) and confocal laser scanning microscopy. The compound eyes arecomposed of hundreds of micron-scale ommatidia closely arranged in ellipsoidal surface.The morphology of each ommatidium is almost uniform and made up of two parts, the upperpart is spherical, the lower is frustum of a cone, with the substrate diameter of20μm, theupper hemisphere diameter ofabout16μmand the overall height ofabout14μm. Thereis nomore tiny structure on the ommatidia surface. Typical hierarchical structure is the structurecharacteristics of water bamboo leaf surface. Macro submillimeter groove structure with thewidth of270μm, the depth of40μm is the first level of structure, and abundant micron-scalepapillae is a second level structure, the heights, widths and spaces of these papillae are about6,10and13μm, respectively. In addition, theleaf surface covered witha layer of nano-scalewax structure is the third level structure. The commonality of the two structures are micron-scale convex structure.In chapter4, bionic models were established based on the feature sizes provided in thethird chapter and then hydrophobic antifogging mechanisms were explained by Cassie model.The proper size, compact arrangement of ommatidia and arc shape of the compound eyesare one of the origins of hydrophobic antifogging function. For Water bamboo leaf, cuticularwax lays the hydrophobic foundation, the microstructure especially micron-scale papillastructures greatly strengthens intrinsic hydrophobic property of surface, forming asuperhydrophobic and antifogging surface. In chapter5, bionic plane compound eyes was fabricated by laser lithographytechnology(LIL)based on three-beam interference on a silicon substrate. Moreover, theeffect of laser fluence and exposure time during the fabrication process on morphology werediscussed. Then the wetting property and antifogging property of this artificial surface werealso mesured. The results shown that laser energy is40mJ and the exposure time is15s areoptimal laser processing parameters. The CA value of water droplets on this artificialbiomimetic surface can reach120deg，showing obvious hydrophobic effect and someantifogging function.In chapter6, artificial water bamboo leaf surfaces were accurately and large areafabricated by duplicating surface using polydimethylsiloxane (PDMS) by Soft lithographymethod, which also exhibit excellent hydrophobicity and strong hydrophobic anti-fogfunction similar to their original counterpart. The maximal water CA value is144.1deg. Theenergy spectrum analysis showed that the surface has no residual F element. In addition, thescope of application of Soft lithography in biomaterial surface replication was also discussed.In chapter7, the bionic nano convex structure arrays were fabricatied on polyesterplastics (PET) surface using Colloidal lithography with a monolayer of Polystyrene (PS)microspheres as masks. Feature sizes of PS microspheres is200nm，350nm and580nmrespectively. Then the static contact angle(CA), roll angle(SA) and antifogging property ofresulted surfaces were measured after fluoride treatment. The results shown that the staticCA value and SA value of PET surface with the feature size of350nm is155±2deg and5deg，showing excellent superhydrophobic and good antifogging function. It can be usedas hydrophobic antifogging surface.In chapter8, this chaper is the conclusion part of this paper, including the mainconclusions of this paper, the main innovations and research prospect.