Mechanism Of Hydrophobicity/Oleophobicity Of Ornamental Plant Leaf Surface And Biomimetic Preparation

In recent years,the super-hydrophobic/oleophobic surface has attracted great attention due to the wide application in industrial,agricultural,environmental,energy,military,aviation/aerospace,and daily life fields.The biomimetic researches based on the micro-morphology and special function of plant surface has been one of the focuses in the fields of biology,material engineering and surface chemistry.The leaves of Kalanchoe blossfeldiana,Tagetes erecta,Phalaenopsis aphrodite,Calendula officinalis,Epipremnum aureum and Euphorbia pulcherrima were collected as the experimental materials of this thesis.The microstructures of the leaves and the biomimetic films were observed by a scanning electron microscope(SEM).The hydrophobicity(water,organic solvent)of the leaves and the biomimetic films was investigated by an optical contact angle(CA)meter.The chemical components of the leaves were determined by a FTIR spectrometer.The mechanism of hydrophobicity/oleophobicity of the plant leaf was discussed from the perspective of biological coupling.Using plant leaves as templates,PVA(polyvinyl alcohol)and PDMS(polydimethylsiloxane)as raw materials,a two-step transcription method was utilized to prepare the biomimetic polymer films with the structure of plant leaf.The results show the leaves of these six plants display hydrophobicity and resistance against the wetting of organic solvents with lower concentrations.The CA of water droplet on the leaf surface of Calendula officinalis is as high as 153°.The CA of droplet of 30% methanol solution on the reverse side of Euphorbia pulcherrimaleaf is higher than 90°.The plant leaf surface exhibits complicated hierarchical microstructure,including primary structure(grid topography),secondary structure(micro-scale rough form)and tertiary structure(submicro/nano-scale rough unit).The plant leaves havethe similar absorption peaks in the infrared spectroscopy,as well as the similar chemical groups and composition.The rough micro/nano-morphology and the natural hydrophobic bases provide the structural and chemical foundation for the complex wettability of the plant leaves.The biomimetic polymer films have the micro-morphology and wettability similar to those on the leaf surface.Plant leaf can be used as a bio-template for biomimetic design of special functional surface.The results may further reveal the wetting mechanism on biological rough surface,and provide insights for biomimetic preparation of novel super-hydrophobic/oleophobic surface and self-cleaning material.