A Review of Methods Based on Nanofluids and Biomimetic Structures for the Optimization of Heat Transfer in Electronic Devices

Nowadays,the utilization rate of electronic products is increasing while showing no obvious sign of reaching a limit.To solve the associated“internal heat generation problem”,scientists have proposed two methods or strategies.The first approach consists of replacing the heat exchange medium with a nanofluid.However,the high surface energy of the nanoparticles makes them prone to accumulate along the heat transfer surface.The second method follows a different approach.It tries to modify the surface structure of the electronic components in order to reduce the fluid-dynamic drag and improve the rate of heat exchange.This article reviews these effects considering different types of nanofluid and different shapes,sizes,and arrangements of“biomimetic grooves”.The idea to use these two methods in a combined fashion(to improve heat transfer and reduce flow resistance at the same time)is also developed and discussed critically to a certain extent.

Mechanical properties and simulated thermal conductivity of biomimetic structured PS-PVD(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7) thermal barrier coatings

Plasma spray physical vapor deposition(PS-PVD)(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7)(GYbZ)thermal barrier coatings(TBCs)exhibited better silicate-phobicity than coatings produced by electron beam physical vapor depo-sition.In combination with PS-PVD and ultrafast laser direct writing technology,biomimetic structured GYbZ TBCs,with a triple-scale micro/nano surface microstructure,were obtained.Laser ablating on the PS-PVD GYbZ coating enhanced the surface roughness,improving its wear resistance without increasing the surface hardness.Furthermore,during the laser ablation processing,numerous nanoparticles were deposited in-situ in the gaps between columns of the coating,reducing the coating Young’s modulus.The simulated temperature field and heat flux field demonstrated that the presence of numerous interfaces between small columns of the PS-PVD coatings is beneficial to thermal insulation.However,laser ablation decreased the coating thickness,reducing the thermal insulation by around 20%-30%as compared to its PS-PVD counterpart,suggesting that a moderate increase in the coating thickness should be considered when designing an efficient TBC system.

Synthesis and application of biomimetic material inspired by diatomite

Inspired by nature,the design and synthesis of novel biomimetic materials are gradually attracting the attention of scientists.Biomimetic materials with excellent performance are widely applied in medical health,industrial production,agricultural planting,aerospace,etc.As a natural porous biomass material,diatomite has the advantages of high porosity,low bulk density,stable chemical property and large surface area.Benefiting from these advantages,it is of great importance to treat diatomite as bionic substrate to synthesize diatomite biomimetic materials,which can be endowed good structure stability and natural mechanical property.It is an ideal option for crystal growth and uniform dispersion of nanostructures,to improve the agglomeration and high cost of nanomaterials.This review briefly introduces our recent achievements on diatomite biomimetic materials in different application fields.In view of its excellent optical,thermal,chemical and mechanical property,diatomite biomimetic materials have shown extensive application potential in various fields of science and engineering,which include catalysis,corrosion protection,microwave adsorption,super-hydrophobicity,pollutant adsorption,energy storage,etc.It demonstrates that diatomite biomimetic materials with different functional properties can be synthesized by diverse chemical means and preparation methods for different application.By composed of inorganic nanomaterial hybrid,this diatomite biomimetic materials display a three-dimensional network structure with diatomite morphology.The design and synthesis of diatomite biomimetic materials provide more potential bionic categories for different applications,which can accelerate the development of low-cost and high-performance biomimetic materials.

Biomimetic leaf structures for ultra-thin electromagnetic wave absorption

Ultra-thin electromagnetic wave(EMW)absorbers present challenging demands on EMW absorption performance.Drawing inspiration from heather leaf structures,this study introduces an innovative design strategy for EMW absorbing material,proposing biomimetic leaf SnO_(2) structures(bio-SnO_(2))on carbon fabric(CF).By employing leaf-shaped SnS2 as precursors,biomimetic leaf SnO_(2) nanostructures are constructed on CF surface after a simple thermal treatment,resulting in bio-SnO_(2)@CF composite.Experimental results indicate that bio-SnO_(2)@CF exhibits an exceptional minimum reflection loss of-54.8 dB at an incredibly thin thickness of 1.2 mm.Radar cross section(RCS)simulations further validate the outstanding EMW attenuation ability of bio-SnO_(2)@CF,attaining a maximum RCS reduction value of 16.9 dBm^(2) at an incident wave angle ofθ=0°.This novel research showcases the biomimetic structural design strategy and its remarkable function in enhancing the EMW absorbing performance at ultra-thin absorber thickness.

Biomimetic Lightweight Design of Legged Robot Hydraulic Drive Unit Shell Inspired by Geometric Shape of Fish Bone Rib Structure

The lightweight design of hydraulic quadruped robots,especially the lightweight design of the leg joint Hydraulic Drive Unit(HDU),can improve the robot's response speed,motion speed,endurance,and load capacity.However,the lightweight design of HDU is a huge challenge due to the need for structural strength.This paper is inspired by the geometric shape of fish bones and biomimetic reinforcing ribs on the surface of the HDU shell are designed to increase its strength and reduce its weight.First,a HDU shell with biomimetic fish bone reinforcing ribs structure is proposed.Then,the MATLAB toolbox and ANSYS finite element analysis module are used to optimize the parameters of the biomimetic reinforcing ribs structure and the overall layout of the shell.Finally,the HDU shell is manufactured using additive manufacturing technology,and a performance testing platform is built to conduct dynamic and static performance tests on the designed HDU.The experimental results show that the HDU with biomimetic fish bone reinforcing ribs has excellent dynamic performance and better static performance than the prototype model,and the weight of the shell is reduced by 20%compared to the prototype model.This work has broad application prospects in the lightweight and high-strength design of closed-pressure vessel components.

Biomimetic chitin hydrogel via chemical transformation

Chitin hydrogel has been recognized as a promising material for various biomedical applications because of its biocompatibility and biodegradability.However,the fabrication of strong chitin hydrogel remains a big challenge because of the insolubility of chitin in many solvents and the reduced chain length of chitin regenerated from solutions.We herein introduce the fabrication of chitin hydrogel with biomimetic structure through the chemical transformation of chitosan,which is a water-soluble deacetylated derivative of chitin.The reacetylation of the amino group in chitosan endows the obtained chitin hydrogel with outstanding resistance to swelling,degradation,extreme temperature and pH conditions,and organic solvents.The chitin hydrogel has excellent mechanical properties while retaining a high water content(more than 95 wt.%).It also shows excellent antifouling performance that it resists the adhesion of proteins,bacteria,blood,and cells.Moreover,as the initial chitosan solution can be feasibly frozen and templated by ice crystals,the chitin hydrogel structure can be either nacre-like or wood-like depending on the freezing method of the precursory chitosan solution.Owing to these anisotropic structures,such chitin hydrogel can exhibit anisotropic mechanics and mass transfer capabilities.The current work provides a rational strategy to fabricate chitin hydrogels and paves the way for its practical applications as a superior biomedical material.

Synthesis Approach and Adsorption Properties of SiOC Nanocomposite by Chitin Templating

Using chitin as the templating material,we obtained layered nanocomposites like shrimp or crab shells via a sol-gel self-assembly process.SEM images show a layered structure and XRD patterns present a typical peak of chitin,which indicates the templating role of chitin in the as-received hybrid samples.Additionally,the layer spacing of chitin/silica hybrid materials is reduced with increasing content of silica.After the heat treatment for carbonization,layered SiOC nanocomposites with mesoporous structures were obtained and showed good dye adsorption performance.The present study demonstrates a reliable and self-assembly synthesis technique for the development of advanced high-performance nanocomposites with biomimetic nanostructures.

A bionic controllable strain membrane for cell stretching at air–liquid interface inspired by papercutting

Lung diseases associated with alveoli,such as acute respiratory distress syndrome,have posed a long-term threat to human health.However,an in vitro model capable of simulating different deformations of the alveoli and a suitable material for mimicking basement membrane are currently lacking.Here,we present an innovative biomimetic controllable strain membrane(BCSM)at an air–liquid interface(ALI)to reconstruct alveolar respiration.The BCSM consists of a high-precision three-dimensional printing melt-electrowritten polycaprolactone(PCL)mesh,coated with a hydrogel substrate—to simulate the important functions(such as stiffness,porosity,wettability,and ALI)of alveolar microenvironments,and seeded pulmonary epithelial cells and vascular endothelial cells on either side,respectively.Inspired by papercutting,the BCSM was fabricated in the plane while it operated in three dimensions.A series of the topological structure of the BCSM was designed to control various local-area strain,mimicking alveolar varied deformation.Lopinavir/ritonavir could reduce Lamin A expression under over-stretch condition,which might be effective in preventing ventilator-induced lung injury.The biomimetic lung-unit model with BCSM has broader application prospects in alveoli-related research in the future,such as in drug toxicology and metabolism.

Multi-functional stimuli-responsive biomimetic flower assembled from CLCE and MOF-based pedals

Simulating the structures and behaviors of living organisms are of great significance to develop novel multi-functional intelligent devices. However, the development of biomimetic devices with complex deformable structures and synergistic properties is still on the way. Herein, we propose a simple and effective approach to create the multi-functional stimuli-responsive biomimetic devices with independently pre-programmable colorful visual patterns, complex geometries and morphable modes. The metal organic framework(MOF)-based composite film acts as a rigidity actuation substrate to support and mechanically guide the spatial configuration of the soft chiral nematic liquid crystal elastomer(CLCE) sheet. We can directly program the structural color of the CLCE sheet by adjusting the thickness distribution without tedious chemical modification. By using this coordination strategy, we fabricate an artificial flower, which exhibits a synergistic effect of both shape transformation and color change like paeonia ‘Coral Sunset’at different flowering stages, and can even perform different flowering behaviors by bending, twisting and curling petals. The assembled bionic flower is innovatively demonstrated to respond to local stimuli of humidity, heat or ultraviolet irradiation. Therefore, the spatial assembly of CLCE combined with functional MOF materials has a wide range of potential application in multi-functional integrated artificial systems.

Biomimetic three-dimensional multilevel nanoarray electrodes with superaerophobicity as efficient bifunctional catalysts for electrochemical water splitting

The design and preparation of cost-effective and durable catalysts for electrochemical water splitting are significant for the development and application of hydrogen production.Herein,inspired by the underwater superaerophobicity of fish scales,a three-dimensional multilevel nanoarray electrode with superaerophobicity was designed and fabricated by the hydrothermal method to solve the bubble shielding effect in electrochemical reactions.Benefiting from the high specific surface area,superaerophobic properties,Al doping,the Al-CoS_(2)nanosheets(NSs)/nickel foam(NF)-30 exhibits outstanding electrocatalytic activity and superior durability for electrochemical water splitting in 1 M KOH.Significantly,the Al-CoS_(2)NSs/NF-30 only required extremely low overpotential of 176 mV for oxygen evolution reaction(OER)to reach a current density of 10 mA·cm^(-2).Al-CoS_(2)NSs/NF-30 was employed as bifunctional electrode for electrochemical water splitting with a cell voltage of 1.58 V at 10 mA·cm^(-2).Meanwhile,Al-CoS_(2) NSs/NF-30 exhibited excellent durability(250 h@10 mA·cm^(-2)and 50 h@100 mA·cm^(-2)).The cobalt-based catalyst(Al-CoS_(2) NSs/NF-30)with superaerophobicity exhibits excellent performance in activity and durability,therefore is a promising electrochemical water splitting catalyst.

Vibration properties and transverse shear characteristics of multibody molded beetle elytron plates

This study utilized cantilever experiments to investigate the vibration properties of multibody molded beetle elytron plates(BEPs),which is a type of biomimetic sandwich plate inspired by beetle elytra;the corresponding shear characteristics were further revealed by a finite element method(FEM). The following results were obtained:(1) Experimental results suggest that the maximum displacement response of the BEPs was about 25% less than that of a honeycomb plate with almost the same first natural frequency,which indicates that a BEP with reasonable structural parameters has the potential to replace a honeycomb plate to achieve better vibration performance;(2) The trabecular structure not only enhanced the shear stiffness of the core layer in column areas but also the skins in the honeycomb wall areas,thus changing the distribution of the shear force in the different components and improving the mechanical performances of the BEP;and(3) Although this enhancement effect from trabeculae was not uniform,the average shear force proportion of the skins(or core structure) in the entire BEP structure was very close to that of the honeycomb plate. Therefore,the shear calculation assumption used for honeycomb plates is still applicable in the BEP.The results provide an experimental basis for the design and application of BEPs and inspiration for the development of related products in vibrational environments.

The flexural property and its synergistic mechanism of multibody molded beetle elytron plates

To improve the applications of beetle elytron plates(BEPs,which are biomimetic sandwich plates inspired by beetle elytra),the flexural performance and its synergistic mechanism of multibody molded BEPs were investigated via cantilever testing and finite element method(FEM).The results are summarized as follows.(1)Although debonding damage causes failure of the multibody molded BEPs and honeycomb plate and the reasonable range of trabecular size for BEPs is narrow,both the optimal loading capacity per mass and failure deformation of the BEPs are over two times those of the honeycomb plate.(2)A flexural synergistic mechanism is revealed in the trabecular-honeycomb core structure of BEPs;this mechanism causes the maximum deformation of core structure to gradually transfer from the honeycomb wall to the trabeculae with the increase inη(the ratio of the trabecular radius to the distance between the center points of two trabeculae),which means the different stretching behaviors in these core structures.(3)Unlike the compressive mechanism of BEPs,by controlling and balancing the deformation degrees of the trabeculae and honeycomb walls,the flexural mechanism achieves a minimum core deformation and an optimal flexural performance.These results suggest a qualitative relationship between the deformation behavior of trabecular-honeycomb core structure and bending performance of the whole BEP,and provide a solid foundation for subsequent research and the considerable application potential of this biomimetic sandwich structure in many fields.