| Phase change materials（PCMs）are widely used owing to their almost constant temperature during the phase change process and their ability to absorb and release a large amount of heat in specific temperature ranges.However,the poor shape stability and low thermal conductivity of PCMs increased their difficulty in use.Nano titanium dioxide is widely used in the field of phase change energy storage owing to its low cost,easy availability,unique photocatalytic activity,and high thermal conductivity.However,due to the small porosity of nano titanium dioxide,it is difficult to achieve the encapsulation of PCMs alone.Therefore,titanium dioxide is often used as an additive in the preparation of PCMs.This study attempts to prepare phase change energy storage materials encapsulated by porous nano titanium dioxide skeleton using chemical methods,which not only enhances the encapsulation effect of PCMs,but also enhances their thermal conductivity and light-to-thermal conversion capabilities.Simultaneously introducing antibacterial,self-cleaning and other characteristics,further enhancing the application value of titanium dioxide in the field of phase change energy storage.This work is divided into the following parts:（1）In order to increase the encapsulation effect of nano titanium dioxide on PCMs,this study introduce poly（methyl methacrylate）（PMMA）in collaboration with nano titanium dioxide for encapsulation of paraffin wax（PW）.Titanium dioxide improves the thermal conductivity of PCMs and serves as a support core for guiding the formation of porous frameworks,resulting in high-performance composite phase change energy storage materials.This section explores the effects of mass of methyl methacrylate（MMA）and nano titanium dioxide on the encapsulation efficiency and thermal conductivity of phase change energy storage materials.Taking into account parameters such as leakage,thermal conductivity,and latent heat,the optimal mass ratio was determined as MMA/TiO2/PW（3.5/1.5/5）,with a leakage rate of only 0.68%and a thermal conductivity increase of 13.3%.After 500 melting solidification cycles,the latent heat of phase change energy storage materials did not significantly decrease,and the presence of titanium dioxide improved the light-to-thermal conversion efficiency of the composite material by 10.5%.（2）In order to give full play to the advantages of nano titanium dioxide and improve the specific surface area of titanium dioxide,this study used the sol-gel method to achieve the in-situ encapsulation of PW with the help of the hydrolysis process of tetrabutyl titanate（TBT）.The oil/water two-phase system formed by PW/water promotes the hydrolysis of TBT to form porous nano titanium dioxide,thereby improving the encapsulation efficiency while intensifying its thermal conductivity.This section explores the effects of different TBT and PW ratios on the thermal conductivity and energy storage performance of phase change energy storage materials.Taking into account various parameters such as leakage rate and thermal conductivity,the optimal mass ratio is determined as PW/TBT（5/3）.The leakage rate of the obtained material is only 0.5%,and the latent heat of phase change reaches 115J/g.After 2600 melting solidification cycles,there is no significant decrease in the latent heat of phase change energy storage materials.In addition,research has shown that the obtained materials possess excellent hydrophobicity and self-cleaning ability at the same time.（3）In order to further clarify the reaction mechanism,this study have established a visualization platform to observe the dynamic evolution laws of dispersion,hydrolysis,encapsulation,and other processes.By observing the hydrolysis process of TBT inside PW using a high-speed camera,and combining the parameters of leakage and phase change latent heat of samples obtained from different reaction conditions and different quality of hydrolysis initiators,a kinetic analysis was conducted on the homogeneous to heterogeneous transformation process during the reaction process.It was found that the reaction temperature affects the reaction speed and thus affects the encapsulation effect of titanium dioxide on PCMs,while the quality of initiators affects the number of small reaction systems,This affects the encapsulation effect.Subsequently,by adding 1 wt.%of other substances（OS）in the initial homogeneous state,combined with the obtained product microstructure,thermal conductivity and other test results,and comparing them with physical mixed samples,the advantages of one-step in-situ encapsulating of titanium dioxide PCMs in this strategy were further verified.The superiority of this strategy in mechanism was verified,and it has the potential value of targeted improvement of corresponding performance parameters for different application scenarios.（4）To clarify the mechanism of intensifying the thermal storage process of phase change energy storage materials reinforced by nano titanium dioxide,this study attempted to explore the influence of reaction conditions on the thermal properties of the obtained materials through structural analysis and thermal storage performance testing.The experiment shows that the drying time has a significant impact on the phase transition temperature and latent heat of the sample.Through the study of the quality,chemical composition,and crystal structure of the sample,it was found that the content of butanol,deionized water,and titanium dioxide in the obtained material directly affects the crystal structure distribution during PW melting and solidification,thereby affecting the phase change temperature and latent heat distribution of the PCMs.（5）In order to further verify the universality and economy of this strategy,this study conducted a scale-up tests on the preparation process,and used atom economy assessment to verify the atom economy of this strategy.Research has shown that this strategy can be scaled up to the kilogram level under laboratory conditions,with a simple environmental factor（s EF）value of only 0.40,basically achieving zero emissions.More importantly,the antibacterial test results show that the presence of titanium dioxide endows phase change energy storage materials with unique antibacterial properties.The experimental results of automotive thermal management show that when the ambient temperature is 40℃,the temperature rise inside the car can be reduced by 4.8℃after using this phase change material. |
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