| Shape-stable composite phase change materials（ss PCMs）can solve the inherent defects of single-phase change materials（PCM）and improve their application prospects.Although the introduction of the carrier can improve the thermal conductivity of the composite phase change material,the thermal conductivity is still low compared with the traditional materials.In addition,the introduction of the carrier changes the motion behavior and crystallization microenvironment of the phase change material,but its influence on the thermophysical properties of the composite phase change material is still unclear.In view of this,combining the heat storage properties of phase change materials with the low thermal conductivity of Kevlar nanofibers（KNFs）aims to obtain Kevlar nanofiber-based composite phase change materials with both heat storage and thermal insulation properties,and explore the structure-activity relationship of composite phase change materials and the influence of confinement effect on their phase transition and crystallization behavior.Using typical fatty acid,fatty alcohol,paraffin（PF）,water-soluble erythritol and polyethylene glycol（PEG）as PCM and Kevlar aerogel（KNA）as confinement carrier,a series of composites phase change materials（PCM/KNA）were prepared by impregnation method.The results show that KNA is suitable for polymer loading,PEG is physically fixed in the pores of KNA,and PEG 10K/KNA and PEG 6K/KNA have good shape stability and thermal stability.The maximal fusion and solidification latent heat for the PEG 10K/KNA are 173.77 J·g-1 and 173.79 J·g-1,while they are 163.10 J·g-1 and 162.33 J·g-1 for PEG 6K/KNA,respectively.In addition,PEG 10K/KNA and PEG6K/KNA have excellent thermal storage,thermal insulation and cycling stability.Due to the hydrogen bond and molecular entanglement between PEG and KNA,a non-melting layer is formed at the interface,resulting in the latent heat of PEG/KNA being lower than the theoretical enthalpy,and the enthalpy efficiency decreases nonlinearly with the decrease of PEG content.In addition,due to the confinement effect and non-melting layer of KNA,the crystallization rate of PEG/KNA is lower than that of PEG,but KNA provides heterogeneous nucleation sites for PEG crystallization,and the crystallization activation energy of PEG/KNA decreases.In order to solve the problem of easy leakage of small-molecule PCM/Kevlar aerogel composite phase change materials,a series of phase change composite membranes（PF/KNF）were prepared by emulsification method using paraffin as the phase change material.The results show that the chemical compatibility between PF and KNF is good,and the PF with lamellar crystallization tendency is embedded between the Kevlar nanofibers film（KNF）KNF lamellae to form a lamellar sandwich structure.When the content of PF is lower than 70 wt%,PF/KNF has good shape stability,and its latent heat of fusion and solidification are 86.52 J·g-1 and 86.32 J·g-1,respectively.The enthalpy of PF/KNF is also lower than the theoretical enthalpy due to the generation of the non-melted layer and the strong confinement of the KNF layered structure,but the enthalpy efficiency decreases linearly with the decrease of the PF content.The study of crystallization kinetics showed that due to the addition of KNF,the arrangement and rotation of paraffin molecules during crystallization were inhibited,the semi-crystallization time of PF/KNF was prolonged,and the crystallization rate was decreased.In order to explore the effect of phase change material-support interaction on the phase change behavior of composite phase change materials,a series of composite films（HA（SA）/KNF）were prepared by solution method using stearic acid（SA）and hexadecanol（HA）as phase change materials.The results show that when the contents of HA and SA are 11.89 wt%and 24.39 wt%,respectively,the heat storage/release behavior of HA/KNF and SA/KNF disappears,the force between SA and carrier KNF is the strongest,and the formed non-melting layer is the thickest.On the other hand,the introduction of KNF changed the crystalline structure and crystallization behavior of SA,and the melting temperature of SA/KNF increased from 65.93°C to 94.01-94.64°C.The strong interaction between the host and the guest resulted in a“second confinement layer”between the“non-melting layer”and the“bulk layer”,and double endothermic/exothermic peaks appeared in the phase transition process.Accordingly,we revised the concept of“non-melting layer”and proposed a“layered phase change model”of Kevlar fiber-based composite phase change material“non-melting layer-second confinement layer-bulk phase layer”.In summary,the confinement effect leads to the formation of a non-melting layer or a second confinement layer in the Kevlar fiber-based composite phase change material,which reduces the crystallization rate and the enthalpy efficiency with the decrease of the PCM content.In the PCM/KNF phase change composite film,the interaction between the phase change material and KNF is as follows:fatty acid>fatty alcohol>n-alkane. |
