Preparation Of PVA/XG Phase Change Hydrogels And Their Temperature Responsiveness

As a kind of temperature-sensitive hydrogel,phase change hydrogel combines the flexibility and skin friendliness of hydrogel and the heat storage property of phase change material,and has the advantages of wide temperature response range,strong thermal cycle reversibility and strong structural design compared with conventional temperature-sensitive hydrogel,showing excellent application potential in biomedicine,photothermal conversion,temperature regulation and health monitoring.However,traditional phase change hydrogels often have poor mechanical properties,poor electrical conductivity,low thermal conductivity,poor thermal cycling stability and low enthalpy of phase change,which limit their applications in the field of temperature monitoring.To address the above problems,in this thesis,xanthan gum/n-eicosane/polyvinyl alcohol（XPP）phase change hydrogels were prepared by the one-pot freeze-thaw method using n-eicosane as the phase change material（PCM）and the emulsification of xanthan gum（XG）to obtain uniform and stable XG/PCM（XP）emulsions and compounded with polyvinyl alcohol（PVA）.the system studied the effects of XG,PCM,and PVA content on the particle size and stability of the mixed emulsion,as well as the microstructure,chemical structure,phase change enthalpy,and thermal stability of the resulting phase change hydrogels.To further improve the temperature responsiveness of XPP phase change hydrogels,xanthan gum/n-eicosane/poly（vinyl alcohol）/boric acid/zinc ion/alumina nanoparticles(XPPB-Zn²⁺-Al₂O₃)phase change hydrogels with dynamic ionic cross-linking,hydrogen bonding and physical filling were constructed by introducing Zn²⁺,boric acid and alumina nanoparticles,The mechanical strength,thermal conductivity,electrical conductivity,temperature responsiveness,and environmental stability of the resulting hydrogels were investigated.The details of the study and the results are as follows:（1）Preparation of xanthan gum/n-eicosane/polyvinyl alcohol phase change hydrogels and their properties:XPP phase change hydrogels were prepared by the emulsification method and one-pot freeze-thaw method using XG as the emulsifier,n-eicosane as the phase change material,and PVA as the hydrogel matrix.The effects of XG,PCM and PVA contents on the particle size,surface charge,dispersion stability and microscopic morphology of the mixed emulsion were analyzed by emulsion index,zeta potential,DLS,etc.It was found that when the XG concentration was 0.8%,the PCM addition was 6 g and the PVA dosage was 30 g,the resulting mixed emulsion had both high PCM loading and excellent dispersion stability,while the tensile strength and strain of prepared XPP hydrogel were 0.18 MPa and 158%.In addition,DSC analysis revealed that the phase change enthalpy of the XPP hydrogel was up to 170.37±2.78 J/g,and the dried gel was placed in an oven at 50℃for 24 h without leakage,showing excellent heat storage and sealing properties.（2）Preparation of highly thermally conductive phase change hydrogels and their temperature responsiveness:To further improve the temperature responsiveness of XPP phase-change hydrogels,XPPB-Zn²⁺-Al₂O₃ phase-change hydrogels were constructed by introducing Zn²⁺,boric acid,and nano-alumina,which combine dynamic ion cross-linking,hydrogen bonding,and physical filling.The mechanical strength,thermal conductivity,electrical conductivity,temperature response,and environmental stability of the hydrogel were systematically investigated.The large number of-COO^-groups in the XG molecules can not only interact with the-OH in the PVA molecular chain through hydrogen bonding,but also form dynamic ion cross-linking reactions with Zn²⁺,which effectively improves the mechanical and electrical properties of the hydrogel.The tensile strength and elongation of the XPPB-Zn²⁺-Al₂O₃ phase change hydrogel was increased to 0.38 MPa and 251.23%,respectively,and its electrical conductivity was as high as 0.84S/m.The addition of nano-alumina not only improves the dispersibility of the PCM,but also increases the thermal conductivity of the hydrogel,which significantly improves the temperature response of the phase-change hydrogel.Its thermal conductivity constant reached 0.558±0.035 W/（m.k）,the phase change enthalpy increased to 180.98±3.12J/g,and the temperature coefficient of resistance（TCR）was 1.23%/℃.At the same time,the resistance change rate of the phase-change hydrogel fluctuates within 1%under different environments such as flatness,bending,pressure,and wind,showing good environmental stability.In addition,the prepared phase-change hydrogel also showed excellent biocompatibility,with a proliferation rate of Cos 7 cells greater than 80%,making it suitable for human body temperature monitoring.