Preparation Of Carbon Dots/Hydroxypropyl Methyl Cellulose And Its Photochromic Properties

Faced with energy crisis and environmental pollution,the automobile industry is undergoing important changes.The development of new energy vehicles,energy-saving and environment-friendly vehicles has attracted extensive attention from the industry and the scientific community.The intelligent window can dynamically adjust its transparency or color according to the ambient temperature,thus realizing the regulation of the sunlight transmittance and effectively saving energy consumption.Therefore,it is particularly important to develop more ideal intelligent window materials.Hydroxypropyl methyl cellulose(HPMC)is a temperature-sensitive polymer with low critical phase change temperature(LCST).When the temperature is lower than LCST,it is transparent,and when the temperature is higher than LCST,it is opaque.Because of its low cost,environmental friendly,degradability and other advantages,it is considered as a potential thermochromic material.However,the LCST of pure HPMC is higher than the ambient temperature and its response rate is slow,which greatly limits its wide application.Carbon dot(CDs)is a new zero-dimensional carbon nanomaterial with a size less than 10 nm.It has many advantages such as good light absorption,abundant surface states,excellent dispersibility and tunability.These advantages make CDs easy to composite with other materials to improve overall performance.Therefore,this paper introduced CDs into HPMC,systematically studied the influence of CDs on the thermochromic performance of HPMC,the specific content is as follows:(1)CDs were incorporated into HPMC by direct stirring at room temperature.The structures of TEM,FTIR,and XPS showed that CDs and HPMC formed a stable composite structure due to the surface functional groups between the two.The synthesized CDs/HPMC has high transparency,indicating that the introduction of carbon dots did not have a significant impact on the transparency of HPMC.More importantly,under light conditions,CDs/HPMC showed fast and reversible transparency changes.This excellent light-induced discoloration is mainly due to the photothermal effect of CDs.In addition,studies have found that the interaction between CDs and HPMC can not only improve the light absorption capacity of the composite structure,but also effectively promote the non-radiative recombination of photo-generated charges,thus further enhancing the photothermal effect of CDs.Therefore,the obtained CDs/HPMC can dynamically switch its transparency according to weather conditions,showing excellent solar control ability.(2)Based on the findings of the first research work,the interaction between CDs and HPMC is expected to reduce the LCST of HPMC,and the addition of chloride ions can significantly promote the breaking of the hydrogen bond between the HPMC molecular chain and the water molecule to reduce the LCST.We prepared chloride-modified CDs(Cl-CDs)by hydrothermal method,in order to achieve the purpose of reducing LCST through the interaction of Cl-CDs and HPMC.The research results show that the C-Cl bond effectively promotes the phase separation between HPMC polymer and water.Compared with pure HPMC,the LCST of Cl-CDs/HPMC has been significantly reduced,and the color change response rate is faster.Cl-CDs/HPMC shows a certain light-induced thermochromic effect,but it is not particularly significant.This work will be further carried out in follow-up research.