Preparation And Properties Of Nano-material Modified Microencapsulated Phase Change Materials Containing N-Tetradecanol

Microencapsulated phase change materials?MicroPCMs?can effectively solve the problems of easy leakage,phase separation,and corrosion during the phase change of conventional single phase change materials.They can be widely used in many fields such as solar energy storage,textile,energy-saving building and functional thermal fluids.Tetradecanol?TD?,also known as myristyl alcohol,is a kind of organic phase change heat storage material,which possesses a very suitable phase change temperature and high latent heat of phase change.Microencapsulation of TD makes it permanent solidification,which greatly broadens the application of TD.This study mainly focuses on the preparation and modification of TD MicroPCMs.For the polarity problem of TD,it is difficult to be coated,so we attempt to use melamine-urea-formaldehyde?MUF?resin to coat TD by in-situ polymerization.Through the methods of adding nano material such as nano TiO₂ and graphene into the wall materials or modifing the surface of microcapsule by silver,the thermal performance and supercooling phenomenon of the microcapsule were improved.Fourier transform infrared spectroscopy?FT-IR?,Raman spectroscopy?Raman?,X-ray diffractometry?XRD?,X-ray energy dispersive spectroscopy?EDS?,scanning electron microscopy?SEM?,laser particle size distribution analyzer,differential scanning calorimetry?DSC?and thermogravimetric analysis?TGA?were used to characterize and analyze the chemical structure,surface morphology,particle size distribution,phase transition properties and thermestability of the microcapsules.The main results were listed as follows:?1?A type of MicroPCMs with MUF as the wall material and TD as the core material were prepared by in-situ polymerization.The prepared microcapsules presented a spherical shape and smooth.The microcapsules'mean diameter was about51.28?m.The phase change enthalpy and phase transition temperature were 116.7 J/g and 41.4°C,respectively.The core content of microcapsules was 55.6%.?2?Using TD as the core material and nano-titania?TiO₂?particles modified MUF as the wall material,the nano-TiO₂ modified phase change microcapsules were prepared by the same method.The volume average particle size of the microcapsules was greatly influenced by the emulsifier concentration.When the addition amount of nano-TiO₂ in the wall material was less than 5 wt%,the microcapsules were spherical and had a smooth surface.With the increasing of TiO₂ content,the latent heat,core content and thermal stability of the modified microcapsules first increased and then decreased.When the Ti O₂ addition was 3 wt%,the melting latent heat reached a maximum of 151.5 J/g.The core content of microcapsule is 72.2%.?3?The phase change material microcapsules were prepared by in-situ polymerization method,with the TD as core material and grapheme-doped melamine-urea-formaldehyde resin as wall material.The effect of the amount of graphene on the properties of the microcapsules was investigated.The surface of the microcapsules became rough and agglomeration occured after the graphene was added.With the increase of the amount of graphene,the latent heat of the microcapsules first increased and then decreased.When the add amount of grapheme was 4 mL,the latent heat of the microcapsules reached the maximum,which was113.8 J/g,and the thermal stability was obviously improved.?4?Silver-coated MUF/n-tetradecanol phase change microcapsules were prepared by the electroless plating approach.The prepared phase change microcapsules exhibied a uniform spherical shape,and the surface of the microcapsules was covered with silver layer.According to XRD analysis,the Ag metal dispersed on the surface of the microcapsules presented the form of elementary substance.The EDS results showed that the coverage of the silver layer on the surface of the microcapsules increased as the amount of silver nitrate increased.DSC results indicated that the melting temperature and the melting latent heat of the microcapsules modified with 0.7 g of silver nitrate were 39.2°C and 126.6 J/g,respectively.Supercooling of the microPCMs coated with silver particles was effectively suppressed,compared with that of microPCMs without Ag.