Preparation And Properties Of Paraffin @SiO₂@Ag Phase Change Microcapsules And Calcium Alginate Composite Fibers

Solid-liquid phase change materials（PCMs）can store and release energy by changing their state and play a very important role in improving the efficient use of energy.So far,PCMs have been widely used in broad areas such as green energy-saving buildings,thermo-regulating fibers and textiles,photovoltaic systems and electronic devices and so on.However,PCMs will have the problems of deterioration of thermophysical properties after several phase change cycles,large volume change during phase change,easy to leak,some PCMs are volatile,toxic and corrosive,etc.Currently,although microencapsulation technology can effectively avoid these problems,the mono-functionality of microencapsulation also limits its use in special environments.Among them,polydopamine（PDA）has been shown to be a novel photothermal conversion material because it has a broad absorption spectrum from ultraviolet（UV）to near infrared（NIR）,while silver is a highly thermally conductive metal known to have catalytic and antimicrobial activity.Therefore,PDA and silver can be deposited on the surface of microcapsules by a simple method,resulting in a phase change microcapsule with efficient photothermal conversion,high thermal conductivity and antibacterial properties,making it a great prospect for application in the field of solar energy and smart textiles.The research of this thesis is as follows:（1）The sol-gel method prepared a paraffin@silica（Pn@Si O₂）microencapsulated phase change material using sodium silicate as the silica precursor.The effects of p H and core-to-shell ratio on the microstructure,crystallization behavior and phase transition properties of Pn@Si O₂ were systematically investigated.At p H=3 and Pn/Si O₂ ratio of 5:1,the synthesized Pn@Si O₂ exhibited well-defined core-shell structure and regularly spherical morphology.The encapsulation rate reached 74.14%with latent heat capacity of about 186.4 J/g due to the formation of perfect microstructure and morphology.In addition,Pn@Si O₂ has excellent heat storage capacity,high thermal stability and excellent shape stability,and shows reliable and durable phase transition properties.（2）In order to make the microcapsules multifunctional,silver metal coated phase change microcapsules were prepared by using the reducing property of PDA.The effects of different concentrations of silver ammonia ions and different reducing agents on silver-plated microcapsules were investigated.The results are as follows:the results by XPS,EDX and SEM show that PDA and silver layers were successfully loaded on the surface of Pn@Si O₂microcapsules.With the increase of silver content on the surface of microcapsules,their thermal conductivity,photothermal conversion performance and antimicrobial ability are substantially improved.The TG and DSC tests showed that the silver coated microcapsules prepared by using potassium sodium tartrate as the reducing agent had the highest silver loading on the shell surface.Multifunctional phase change energy storage fabrics were prepared by compounding silver-plated microcapsules with calcium alginate using a wet spinning method in order to enable the application of the prepared silver-plated microcapsules.The effect of silver-plated microcapsule content on various aspects of the properties of calcium alginate composite fibers was investigated.It was shown that the microcapsules were firmly embedded inside the calcium alginate matrix,and the calcium alginate could provide protection to the phase change microcapsules,further improving the impermeability of the phase change material.When the microcapsule content is 70 wt%,the enthalpyΔH_m is 64.3 J/g,which has excellent energy storage performance.As shown by the results of photothermal conversion tests and infrared thermographic monitoring,the photothermal conversion and heat transfer capability of the phase change composite fibers can be greatly promoted by loading PDA and silver on the surface of the microcapsules.