Preparation And Applied Research Of Hydrophobic Function Materials In Refrigerators

Hydrophobic materials have demonstrated broad applicaiton prospects in self-cleaning,antifrost,anti-icing,etc.However,the inherent disadvantages of the hydrophobic materials,such as instability of property thate the micro-nano structure fragile vulnerable corrosion and wear,high-price,limit hydrophobic materials applications in industrial production and daily life.Hence,structure the stable hydrophobic materials was one of most promising way to application in production due to its simplicity and lower cost.Compared to the old energy efficiency standard,the energy consumption of new refrigerator for one level needs to increase by about 14%,while the frosting-defrost process would contribute to about 3%～5%decrease.In this paper,a simple method was applied to prepare hydrophobic material using hydroxyl-terminated silicone modified with silica nanoparticles at high temperature,and further mixing the nanoparticles with the preferred coating substrate to improve the frost problem of refrigerator evaporator.With the rise of intellectual products and smart home,the refrigerator with WiFi hotspot and other wireless devices is also a development tendency.At the same time,the operation of these devices will bring lots of electromagnetic interference pollution.The electromagnetic interference(EMI)not only affects the performance of electronic devices and information security,but also harmful to human beings.To address these issues,electromagnetic interference(EMI)shielding fabrics,base of the great advantages for breathable,soft and easily functionalized,has a better application prospect in many complex applications as intelligent appliances,portable electronics and wearable textiles.However,the performance stability and durability of electromagnetic shield fabric in refrigerator with high humidity environment are against the greatest challenge.The application performance of electromagnetic shielding fabrics with excellent hydrophobic properties will be improved.In this study,a flexible composite cotton with ultraefficient EMI SE,low reflection characteristics and hydrophobic performance by constructing a gradient shielding network with Ag nanowires.The gradient structure can be automatically formed during the composite formation process because of the gravitation effect.Then Polyvinylidene Fluoride(PVDF),which is a fluorine material that can not only provide low surface energy but also can structure roughness surface,was modified on cotton by one step.This thesis includes the following four parts:1.The effect of the refrigerating modes on the frost formation mechanism and defrosting process of refrigerator with different cooling mode was studied experimentally.For air-cooled refrigerator,frost layer mainly occurs on the refrigerated evaporator parts.When the refrigerator ran in equilibrium state,this space belongs to the low temperature and high humidity enviroment.The occurrence time and location of the initial frost crystal in the evaporator and the state of water droplets in the defrosting process were recorded in the test.The frosting performance and the dynamic frost formation process on direct cooling refrigerator were also investigated.The summation of the frost formation mechanism of refrigerators with different refrigeration methods could provides a theoretical basis for selecting frost suppression methods and improving the efficiency of refrigeration system under various frost conditons.2.In this study,polydimethylsiloxane modified SiO2/organic silicon sol(PDMS-SiO2/SS)hybrid coating with frosting inhibition was synthesized by using polydimethylsiloxanes(PDMS400)modified silica particles(SiO2)and the organic silicon sol(SS)as the raw materials for air-cooled refrigerator.The amount of PDMS-SiO2 is a critical factor affect to surface hydrophobic performance of the PDMS-SiO2/SS hybrid coatings,and the maximum water contact angle is 152.82°.In addition,the frost test of PDMS-SiO2/SS hybrid coating was carried out on a refrigerator evaporator.The results show that the coating not merely delays the frost crystals time but also increases the frost layer process time.Meanwhile,the defrost water droplets are easy to roll off from coating surface which is benefit for frost suppression performance of the next refrigeration cycle.This implies that the PDMS-SiO2/SS hybrid coating has a better anti-frosting performance3.In this study,a simple synthesis method was applied to form a branch and tendril structure by using hydroxyl-terminated silicone sol modified silica nanoparticles at high temperature,followed by mixing with fluoro-containing polyacrylate emulsion(PFA)to obtained PDMS-SiO2/PFA hybrid coating for direct cooling refrigerator.The hydrophobic performance of the PDMS-SiO2/PFA coating was further enhanced through the synergistic action of Si-O and F group.PDMS-SiO2/PFA sample could construct hydrophobic surface on various substrates because of the good adhesion of acrylate group in iron,aluminum and plastic substrates.In order to verify the frost suppression stability of the PDMS-SiO2/PFA hybrid coating,the refrigerator worked continuously for more than 2800 minutes(more than ten frosting and defrosting cycles),which indicates the potential application of this coating in the field of frost suppression.4.In this paper,a flexible Electromagnetic interference(EMI)Cotton/AgNWs/PVDF@GO composite fabric with good hydrophobic performance was realized by constructing positive silver nanowires(AgNWs)gradient and negative poly(vinylidene fluoride)(PVDF)microspheres gradient structure to meet the dual demands of electromagnetic shielding and hydrophobic performance for smart refrigerators.The upper surface of the composite cotton fabric is rich in PVDF microspheres and poor in AgNWs,which can not only ensure the excellent hydrophobic property,but also increase the impedance matching resulting in a low reflection loss,while the dense AgNWs network deposited at the bottom can provide a good EMI shielding performance.Furthermore,the degree of the gradient structure can be controlled by regulating the AgNWs loadings and the sedimentation time during the dip-coating process.The Cotton/AgNWs/PVDF composite fabric can exceed an excellent EMI SET up to 50 dB with a low R value only 0.39 at 10 GHz.This gradient structure provides a strategy for designing hydrophobic EMI shielding materials with low reflection characteristics in cotton fabric.