Anti-icing Behaviors And Mechanism Of Engineering Superhydrophobic Self-cleaning Coatings

Low temperature freezing disaster is a serious challenge for the fields of power transmission and communication,the development of engineering superhydrophobic self-cleaning anti-icing coating materials show important scientific significance and application value,as traditional de-icing methods can not fundamentally solve the icing problem.Although important progress has been made in the research of superhydrophobic coating materials at home and abroad,the application of superhydrophobic materials in engineering anti-icing is still in the“bottleneck period”.The main reason is that the simple preparation of engineering superhydrophobic coating materials and the anti-icing behaviors and mechanism of these materials in complex natural freezing environment are not yet clear.Based on the previous research,this thesis systematically studied the icing/de-icing behaviors and anti-icing mechanism of superhydrophobic self-cleaning coatings in the multi-factor freezing rain environment,and further compared the anti-icing engineering demonstration with the laboratory research.The main research results are shown as follows:1.The PTFE/PPS superhydrophobic/hydrophobic coatings with micro-nanometer textures were constructed on various substrates such as metal and glass by using traditional coating curing process.The superhydrophobic surfaces?WCA=134-163°?with different wettabilities?WCA,WSA?,microstructures and air cushion were obtained by tuning the micro-scale structures such as micro-mastoids and network pores,and the nano-scale structures such as nano-fibers,nano-pimples and nano-pores.The microstructure regulation was realized by changing the composition ratio and the curing cooling process,combining the“phase separation”with the“polymer crystallization interference”principles.Furthermore,the engineering properties of these coating materials such as subtrate matching/large size preparation,mechanical properties,water mediaum resistance and wear resistance and their synergies were studied systematically.These results lay good material foundation for subsequent anti-icing mechanism study and anti-icing engineering demonstration.2.Aiming to solve the problem that the anti-icing/icephobic behaviors and mechanism of superhydrophobic surfaces/interfaces can not be evaluated scientifically,easily and reasonably due to big diffence between the simulated freezing environment in laboratory and natural freezing environment,an on-line monitoring method for multi-factor low-temperature icing test was established innovatively by synergy of the“multi-factor natural freezing environment?including temperature,humidity,rain,water vapor,wind,vibration,swing,etc.?”,the“icing/de-icing real-time monitoring”and the“ice adhesion/desorption test”.The behaviors of wetting,spreading,icing of water droplets/water vapor and ice melting/desorption on surfaces with different wettabilities in the freezing rain environment can be microscopic dynamic tracked,and the ice adhesion of the interfaces can be detected,laying good method foundation for subsequent anti-icing mechanism study.3.The effects of environmental humidity,water medium,freezing rain environment,surface hydrophobicity?air cushion?and nanostructures/nanopores on icing-delay of superhydrophobic self-cleaning coatings were systematically studied.The superhydrophobic coating was more conducive to inhibit/delay ice nucleation of sessile water droplets than the hydrophobic coating and hydrophilic substrate?delay 10-40min?in low temperture and high humidity environments?0^-4^oC,40%⁶0%RH?.The superhydrophobic steel pipe surface shows good anti-icing effect in the simulated freezing rain environment as the amount of ice was only 40-50%of that on bare steel pipe.Furthermore,the effect of nanostructures,nano-pores and nano-scale roughness on icing-delay was found to be much less than the wetting property?air cushion?,by comparing the icing-delay behaviors of hydrophobic surfaces with different nanostructures.4.A physical model of“air cushion convection inhibiting icing”was innovatively proposed,the internal interference mechanism of air cushion on icing-delay was fully explained from both static and dynamic action.The static action only increases the ice nucleation Gibbs free energy barrier and reduces the nucleation rate,while the dynamic action means that Gibbs free energy of water droplets(G_water)increased with the entropy of air(S_air)derived from heat and mass transfer between warmer air underneath water droplets and colder surrounding air,resulting in difficulty of ice nucleation.Only when air cushion convection disappears can ice nucleation be triggered on suitable Gibbs free energy??G?conditions?ie.,ice nucleation delay by air cushion convection?.5.The relationship between wettability,micro-nanostructures,air cushion of superhydrophobic/hydrophobic surfaces and the ice melting/desorption behaviors of water droplets/raindrops on these surfaces was systematically studied.The ice beads began to melt from the interface,and the total melting time of spherical ice beads on superhydrophobic surfaces was longer than hydrophobic surfaces?about 1 min?as the interfacial thermal conductivity was lower.The ice on superhydrophobic surfaces was easier to desorb than hydrophilic/hydrophobic surfaces?about 1-3min earlier?under the freezing rain condition and interference conditions of wind and vibration.6.The modes for the influences of dynamic wetting?non-continuous water film?and the surface micro-network pores and nano-scale structures on de-icing were proposed.The easy ice desoption on surperhydrophobic surfaces was related with the diffculty to form ring-like ice on these surfaces in the low temperature freezing rain environment.The ice adhesion of the interface was significantly correlated with the surface nanostructures and pore size distribution.Nano-fibers were more favorable to reduce ice adhesion than nano-pimples when the micro-scale structures were the same.Ice was easier to desorb from the interface with wider pore size distribution range?20-100?m?,since the difference of ice expansion deformation in these microstructures caused the depth difference of microscopic pinning.7.The preliminary anti-icing engineering demonstration shows that the superhydrophobic glass insulator has a good“anti-icing”effect?up to 60%?in the simulated low temperature freezing rain environment.The ice on superhydrophobic steel plate for high-speed railways can be easily removed by hand after the water vapor icing test.The engineering demonstration results are consistent with laboratory anti-icing behaviors and theory.These results will provide a theretical basis and technical support for enhancing the technical level of anti-icing disasters in the fields of power transmission,communication and traffic.