| With the development of information technology and the popularization of personal computers,panel computer and mobile phones,electronic screens are frequently used.liquid crystal display(LCD)technology with glass as the main substrate is the mainstream technology in the field of display screen today.However,the specular reflection on the surface of the LCD screen is the main cause of glare,which can cause serious visual damage.In some special environments,for example,when a fighter jet is flying at a high altitude,the sunlight may cause a strong glare on the surface of the airborne display,and the pilot will be temporarily blind.Therefore,the research of anti-glare technology is of great significance for daily life,military equipment,and so on.In addition,strong reflections will reduce the conversion efficiency of solar energy equipment,even limit its further development.Hence the design and manufacture of antireflection surfaces need to be researched urgently.In order to solve the problem of excessive surface reflection,antireflection technology has been vigorously developed,and it is achieved by antireflection coatings and antireflection structures.Most antireflection coatings rely on quarter-wave interference extinction to achieve antireflection.This technology is relatively mature,however,there are problems such as low efficiency,small actual bands,weak mechanical strength,and poor durability.As for the antireflection structure,it can realize the light trapping effect by constructing a surface texture structure to reflect the incident light multiple times and extend its light path.This method has relatively good antireflection effect in broadband,but it is extremely difficult to design and optimize its structure and parameters,hence it is relatively difficult to develop.Based on current technology bottlenecks,bionic thoughts can provide a perfect solution.Creatures have experienced natural selection for thousands of years,and its body surface structure has long evolved into the optimal combination under a specific living environment.The study of bioinspired functional surfaces or structures can open up a shortcut for artificially constructing functionalized surfaces.In order to avoid natural enemies and achieve camouflage,cicadas living in the tropics have acquired natural high transmission and antireflection characteristics during the long process of natural evolution.The surface nanostructure of the cicada balances the high transparency and low reflectivity performance requirements of the material,has shown a unique advantagement in antireflection.Based on the antireflection performance of cicada wings,this paper deeply explores the interaction between the nanostructure and incident light to reveal the internal antireflection mechanism of the cicada wings.Based on this,the design and optimization of the bioinspired antireflection structured functional surface are carried out,aiming to acheve the preparation and application of biomimetic antireflection materials.However,in this process,there are plenty of challenges to face,such as unknown mechanism,crude preparation,performance degradation,and complex working conditions.In order to solve these problems,the research content of this paper will be divided into five parts:(1)The functional structure of the cicada wing surface and its antireflection mechanism.The surface array structure of cicada wings contains a profound antireflection mechanism,but the complicated surface optical effect is a nodus in the study of the mechanism.In this paper,the dome cone array structure on the surface of the cicada wing(Cacada sp12)was observed by SEM,AFM and other methods.The refractive index distribution of the structural interface was quantitatively calculated through the equivalent medium theory.Besides,the threedimensional model and FDTD simulation were performed to obtain the electric field distribution and spectral data of the array structure.Based on this,the antireflection mechanism of the dome cone array structure on cicada wing is fully revealed,and the sudden refractive index change at the interface is eliminated,hence the Fresnel reflection is depressed.(2)Precise preparation of bioinspired antireflection structures.Limited by the antireflection mechanism,the optical structure has extremely strict requirements on its shape and size during the preparation.The subwavelength array structure on cicada wing is too small to fabricate accurately,not to mention the performance improvement of interface.In response to this problem,this work chooses biological materials as the original template to ensure the accuracy of the structure.Relying on the improved sol-gel technology and high-temperature acid etching technology,the biological array structure is transferred to the polymer substrate successfully through the two-step replication.The exact structure reproduction and perfect function inheritance of bioinspired antireflection material to the cicada wing were determined by means of morphology observation,spectral measurement,fog measurement and contact angle measurement.In a word,the preliminary exploration of bionic design and precise preparation is realized.(3)Research on the large-area controllable preparation of the bioinspired optical gradient structure and its scale-insensitive effect.The application of biomimetic functional materials is often limited due to the small effective structural area.Therefore,the large-area preparation technology of nanostructures has always been a research hotspot.In this paper,the imprinting technology with recycling porous template could realize the efficient and rapid replication of the bioinspired structure,and it accomplishes large-area controllable preparation.In addition,inspired by the cicada wing structure,plenty of bionic antireflection optical gradient structures are optimized and prepared.Quantitative calculations and FDTD simulation analysis reveales the scale-insensitive effect of the bioinspired optical gradient structure.When the structure parameters are in subwavelength level,the surface performs high transmission and low reflection.However,when it is in nearwavelength level,the surface displays light trapping effect and the reflection is reduced.Its specific antireflection strategy at different scales puts forward new schemes for the design of antireflection structures under different requirements.(4)Bioinspired reversible antireflection material.The deformation of the structure under the action of external force will cause the destruction of the surface performance,which is one of the reasons for the failure of most microscopic arrays.It is also a problem that the antireflection structure is widely faced in its research and development.To solve the problem,this work optimizes the choice of basic materials,using transparent polymer materials that perform shape memory recovery near human body temperature to assist in the process of preparation.The bioinspired reversible antireflection material has been fully characterized by thermomechanical tests,reversible antireflection tests,and cycle stability tests,proving its satisfactory deformation recovery ability.This coupling method of material and structure guarantees the functionality and stability of the bioinspired antireflection material to the greatest extent,and solves the problem of attenuation of antireflection performance caused by the deformation of the micro-array structure at the interface.(5)Multifunctional treatment and application exploration of biomimetic antireflection surface.When facing actual working conditions,a single function antireflection surface is often inadequate.There are three reasons: First,the actual environment is faced with the adhesion of dust,impurities,water mist,etc.,which means that the structure at the interface will be buried and difficult to take effect;Secondly,the structure of the selected material makes the structure less effective in the absorption of light energy,making the improvement of photothermal conversion difficult;Thirdly,the design and application of bioinspired reversible antireflection materials in touch screens and smart materials are restricted due to their own insulation.In response to these problems,this work uses various coating technologies such as spraying hydrophobic silica,ion sputtering gold nano-layers,and spin-coating conductive polymers to make the bioinspired antireflection surface upgrade to multifunctional surfaces.Spectral analysis,contact angle test,photothermal test and stress-strain response are used to prove that the modified surface has obtained a series of properties such as high transparency,self-cleaning,light trapping,energy absorption,and electrical conductivity.This work with the aid of bionic thought is dedicated to the problems caused by excessive reflection in our actual production and life.The innovation lies in: The high transmission and antireflection mechanism of the cicada wing is systematically revealed through theoretical calculations and simulations;the size limitation of biological materials and the bottleneck of industrial processing are broken,and the large-area controllable preparation of subwavelength structure is realized;In terms of structure parameter optimization,a variety of bionic optical gradient structures are designed and their scales-insensitive antireflection effect is revealed,which can reduce the difficulty of industrial processing;Finally,a material-structure dualcoupled bionic structure is design.Meanwhile,three types of multifunctional antireflection materials are researched through different surface modification treatments,making preliminary explorations in new fields such as function-oriented antireflective structures and bionic smart materials. |
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