A Heat-storing, Temperature-adjusting And Color-changing Composite Film With Temperature Response "breathing" Pores

Multi-functional intelligent film with temperature-sensitive,latent heat storage and thermochromic properties have attracted extensive attentions,which have broad application prospects in the fields of thermal regulation clothing,intelligent clothing and wearable temperature sensors.In this reaserch,thermochromic micro/nano encapsuled phase change materials（TC-M/NPCMs）were prepared by in-situ polymerization with crystalline violet lactone（CVL）,bisphenol-A（BPA）and n-tetradecanol as core materials and melamine-formaldehyde resin as shell materials.TC-M/NPCMs as functional additives,a series of flexible reversible thermochromic membranes with excellent latent heat storage and temperature regulation properties were prepared.In the composite film,polyvinyl alcohol/water-soluble polyurethane（PVA/WPU）composite material was served as polymer matrix material,and trimesoyl chloride（TMC）was used to modify the surface of the composite film to improve its surface hydrophobicity.Morphology and performances of flexible thermochromic membranes were experimentally investigated using field-emission scanning electron microscope（FE-SEM）,digital camera,differential scanning calorimeter（DSC）and thermogravimetric analyzer（TGA）et al.A facile temperature colorimeter was designed and fabricated,by using the flexible thermochromic membrane,which could provide a research basis served as a promising wearable temperature sensor.In order to optimize the synthesis process and improve the dispersibility of additives,thermochromic nano capsuled phase change materials（TC-NPCMs）with an optimal core-wall ratio of 2:1,an optimal emulsifier p H of 5.0 and an average particle size of 350 nm were prepared by adjusting the core-shell ratio and emulsifying p H.The thermochromic nanofibrous membrane（TC-NFMs）with high energy storage density and excellent heat storage and themal regulation performance was fabricated by electrospinning technology by adding TC-NPCMs as functional additive into PVA/WPU spinning solution.And the methylether melamine formaldehyde（MMF）was innovatively applied to improve the water resistance of TC-NFMs.With only 7 wt%TC-NPCMs added,the thermal enthalpy of nanofibrous membrane was up to 44.9 J/g,with excellent heat storage performance.Even after100^th heating and cooling cycle experiments,TC-NFMs still maintained its high enthalpy value.A two-step method was used to prepare the temperature-sensitive polyurethane（PU）film by using polyethylene glycol（PEG）with crystalline structure as the soft segment and adjusting the response temperature of PU film by adjusting the molecular weight of PEG.TC-NFM was compounded with the PU film to prepare a thermal storage,temperature-adjusting and thermochromic composite film with temperature-sensitive“breathing”stomata.When the temperature was lower than the comfortable temperature of human body,the composite membrane could not only store the heat generated by human body and prevent the waste of heat,but also release it back to the skin surface when the human body needs it.Above 38 ^oC,water vapor produced by the human body could be released into the outside world through the composite membrane.Therefore,the composite film prepared in this study has the intelligent characteristics of low temperature heat preservation,high temperature moisture permeability,heat storage,temperature regulation and temperature indication.