Construction Of Thermosensitive PNIPAm Hydrogel System And Application Of Smart Window

As the continued growth of the world population has greatly increased global energy demand,more efficient use of energy is crucial.At present,the loss of building energy accounts for more than 40%of the total energy loss in developed countries,which has exceeded the energy loss of transportation,heating and industry.Reducing these energy losses while maintaining indoor comfort is a major challenge for sustainability.Among building components,however,windows are one of the least energy-efficient components.At present,smart windows have received wide attention from researchers because of their potentially significant contribution to saving building energy consumption.A thermochromic smart window does not need to consume additional energy and can change color with the temperature of the external environment（glass is transparent when the weather is cold,the glass will change color when the weather is in hot weather）,which is one of the most suitable smart windows for the preparation of energy-saving equipment.In recent years,the poly-N-isopropyl acrylamide（PNIPAm）thermochromic smart window has attracted special attention from researchers due to its simple preparation method and excellent optical performance.Previously,this field has mainly focused on the study of thermochromic performance,and the anti-drying/frost resistance,thermal response rate and durability of smart windows have rarely been studied in practice.In this paper,we successfully constructed the PNIPAm-hydroxypropyl cellulose（HPC）chain entanglement hydrogel smart energy-saving window around the temperature-sensitive PNIPAm thermochromic material.The results show that since the chain entanglement and the introduced hydrogen bonds do not hinder the movement of the polymer network structure,the smart function of PNIPAm-HPC composite hydrogel is significantly improved,with better cycle stability,faster response and increased resistance of the polymer.The Young modulus and toughness of this novel PNIPAm-HPC composite hydrogel were about 10 and 22fold compared to the pure PNIPAm hydrogel.More importantly,it can save 16.1%of heating/cooling energy per year compared with ordinary transparent glass and commercial low-energy glass.In addition,we further designed a temperature-sensitive W-VO₂/PNIPAm-HPC composite hydrogel smart window.The W-VO₂/PNIPAm-HPC composite hydrogel smart window showed excellent visible light transmittance(T_lum)（20℃）of 87.16%and high solar energy modulation efficiency(ΔT_sol)（20-40℃）of 65.71%.The smart window maintains a high solar rays modulation capability even after more than heating/cooling cycles and also shows excellent durability.In addition,it has a high infrared modulation rate(ΔT_IR)（20-40℃）of 46.50%.Meanwhile,the introduction of HPC makes the volume shrinkage rate of the pure PNIPAm hydrogel only about 8.5%before and after the phase change.This topic prepares a smart energy-saving window without additional energy consumption in the use process.This smart energy-saving window can be adjusted,prepared and installation cost,and long service life.in addition,different from the traditional preparation method,the physical chain entanglement method has simple operation and environmental protection;and it also provides a new vision for the development of smart energy-saving building glass.