Experimental Preparation And Thermal Conductivity Measurement Of Poly N-isopropylacrylamide And Polyacrylamide Hydrogels

Recently,hydrogels have been widely used in biomedicine,sensors,actuators and many other fields due to their good mechanical properties,excellent biocompatibility,and stimulus response characteristics.With the development of these fields,heat dissipation is becoming a problem that cannot be ignored.The thermal properties of poly（N-isopropylacrylamide）and polyacrylamide hydrogel are explored in this work.We prepared the sample of the poly（N-isopropylacrylamide）hydrogel and measured the varied thermal conductivity of the hydrogel along with the different temperature and water content by using the transient hot wire method.The results indicate that the thermal conductivity of hydrogels will change correspondingly during the phase transition process.After the shrinking process,the thermal conductivity of the hydrogel will drop sharply from0.51 Wm^-1K^-1 to 0.35 Wm^-1K^-1,and the thermal conductivity ratio is calculated to be 1.7.The main reason for the varied thermal conductivity of the hydrogel is the different water content of the hydrogel before and after the phase transition process.We measured the trend of the thermal conductivity change in different water content and compared it with the results that calculated by effective medium theory.When the water content of the hydrogel is increased from 38 wt%to 90 wt%,the thermal conductivity will also increase from 0.35 Wm^-1K^-1 to0.50 Wm^-1K^-1,and they show a strong linear relationship.We also used themolecular dynamics simulations to predict the thermal conductivity of hydrogels in different water contents and found that they have the same trend with the experimental measurements and theoretical calculations.This paper further studies the application prospect of using it as the thermal switch.The thermal switch ratio of this hydrogel can reach about 3.5.Furthermore,the dynamic response property of this thermal switch is also studied.For the polyacrylamide hydrogel,the thermal conductivity change by doping different content of copper oxide,carbon black particles were studied in this work.The relationship of thermal conductivity and temperatures was also studied by experimental measurement.The result shows that the thermal conductivity of the hydrogel could be improved about 40%by doping copper oxide particles or carbon black particles,and the thermal conductivity was increased with the doping content.The thermal conductivity of hydrogel does not show obvious change in different temperatures,and temperature-dependent characteristic is very weak in this hydrogel.This is mainly due to the morphological change of the polymer chain caused by temperature does not affect the average phonon mean free path in the amorphous polymer.This work proposes a change in the thermal properties of the thermally responsive hydrogel before and after the phase change and proposes a new application method.The improvement of the thermal properties of doped hydrogels also provides an effective reference for the corresponding research.