Preparation And Properties Of Composite Phase Change Materials With One-dimensional Micro-nano Confined Structure

Phase change material(PCM)is a kind of materials with a high heat of fusion which,melting and solidifying at a certain temperature,are capable of storing and releasing large amounts of thermal energy when their phase changes from solid state to liquid state or vice versa.Also,this enables thermal energy being stored from one process or period of time and used at a later point in time or transferred to a different location,which shows great potential for various applications such as solar energy saving,industrial waste heat recovery,industry waste heat recovery,building energy saving,and electronic temperature control equipment.Commercially available PCM suffers from the drawbacks of leakage,and poor thermal conductivity.Although confined packaging technology can effectively solve the problem of PCM leakage,there are still some theoretical and practical problems to be solved in the field of high energy storage density,high power composite PCM.In this paper,one-dimensional PVA nanofibers,halloysite nanotubes(HNT)and kapok hollow microtubules(KF)were used as carriers to confine PCM,and effective heat transfer pathways are built through thermal conductive nanoparticles to achieve rapid storage and release of heat energy.Furthermore,a carbon microtube aerogel(CKF@Fe3O4)was prepared to achieve high PCM encapsulation and multi-function regulation.The multifunctional platform integrated with heat,light and magnetic energy conversion,has been constructed to achieve a novel eco-friendly composite PCM with thermal energy capacity and thermal energy release efficiency.The conclusions are as follows:(1)Eco-friendly phase change fiber(PCF)based on PEG/PVA was prepared by directly electrospinning the PEG/PVA aqueous solution.Ag nanoparticle(Ag NP)was introduced by adding Ag NO3 in spinning solution,and UV irradiating the obtained PCF.Moreover,the surface of PCF can be further crosslinked using glutaraldehyde as an efficient crosslinker,and the long-term service durability of the PCF is expected to be further enhanced.The CF-3 showed melting temperature of 45.9°C and latent heat of 67.5 J/g with excellent thermal,chemical,and morphological stability after 2000melting and cooling cycles.The crosslinking process has no obvious influence on the micromorphology of the composite fiber except for significantly improving the thermal stability and tensile strength.The thermal energy storage times of CF-1 and CF-3 were 15.8%and 23.5%lower than that of CF-0,respectively.On the other hand,the thermal energy release times of CF-1 and CF-3 were 20.6%and 26.0%lower than that of CF-0,respectively.The electrospinning process used in this study did not require any organic solvent,and hence was environmentally friendly and non-hazardous.(2)Ag NP across the optimal 1D HNT hybrid nanostructure was successfully constructed via combining chemical reduction and self-assembly techniques and then applied to prepare PEG/HNT@Ag composite PCM(CPM)by a simple vacuum impregnation method.Compared with HNT@Ag-1,the specific surface area of CPM-1 was dramatically decreased from 43.37 m~2/g to 0.57 m~2/g.The CPM-3melted/crystallized at 22.6/17.8 ~oC with a latent heat of 71.3/68.1 J/g,respectively.Compared with PEG,the thermal conductivity of CPM-3 with Ag NP doping amount of 3.3 wt%was significantly enhanced from 0.293 to 0.902 W/m K,which was increased by 2.08 times.The CPM exhibited robust thermal reliability without latent heat capacity deterioration or phase transition temperature variation with respect to2000 times thermal cycling.Moreover,the PEG/HNT@Ag hierarchical composite also demonstrates pronounced antibacterial activity against E.coli.(3)A novel microtubule-encapsulated PCM(MTPCM)was prepared by embedding LA into KF microtubules that had been pre-coated with Ag NP.KF microtubule was cylindrical,smooth and wrinkle free.The outer diameter and wall thickness of the microtubule were 18-22 and 0.5-0.8?m,respectively,and the hollowness is as high as 90 vol%.After loading LA,the volume of micropores of LA/KF@Ag MTPCM larger than 20?m decreased significantly.The volume of mercury injection was greatly reduced from 19.41 m L/g to 3.73 m L/g.The filling rate of PCM in microtubes was 81 vol%;The latent heats of melting of LA/KF and LA/KF@Ag MTPCM were 153.5 and 146.8 J/g,respectively,which were 86.5%and82.7%that of LA.Compared with LA/KF MTPCM,the thermal conductivity of the LA/KF@Ag MTPCM increased by 92.3%due to the introduction of Ag NP,the resulted heat storage/release efficiency increased by 15.8%and 23.5%,respectively.(4)Magnetic carbon hollow microtubule aerogel CKF@Fe3O4 was prepared by in-situ growth and simultaneous carbonization method.The composite aerogel had ultra-low density,excellent compression reversibility,and high conductivity sensitivity.The saturation magnetizations of CKF@Fe3O4-5 and CKF@Fe3O4-30 are 3.4 and 52.5emu/g,respectively.When the matching thickness is 5.5 mm,the microwave absorption peak of LA/CKF@Fe3O4-30 at f=8.4 GHz reached-17.3 d B,and the bandwidth of-10 d B was 1.7 GHz,indicating that the composite material exhibit excellent microwave absorption performance and wide effective absorption bandwidth.The latent heat of LA/CKF and LA/CKF@Fe3O4-30 is as high as 171.1 and 161.9J/g which were 97.5%and 92.3%that of LA.The novel composite PCM can effectively absorb solar radiation and electromagnetic wave,thereby converting the solar and electromagnetic energy into thermal energy,and then dispatch these energy to surroundings through the carbon based 3D interpenetrating network,and successfully store that energy in the form of latent heat through the phase transition of embedded PCM.Thus,the composite PCM in this study is a multifunctional energy harvester,and is expected to expand the application field of composite phase change materials.