Fabrication And Application Of Multifunctional Nanostructured Form Stable Phase Change Thermal Energy Storage Materials

Phase change materials（PCMs）have the capacity to store and release large latent heat within a slight temperature change through phase transition,which have been widely applied in the fields of thermal energy storage and temperature control.The widespread applications of most PCMs are limited by their inherent leakage defects.Confining PCMs with the supporting materials via microencapsulation,porous frameworks encapsulation to prepare form stable phase change materials（FSPCMs）has been determined as an effective strategy to solve the leakage issue.FSPCMs can effectively store and release thermal energy during its isothermal phase change process while maintaining the form stability.However,the traditional FSPCMs can only respond to temperature changes,which greatly limits their application in obtaining thermal energy via other stimuli besides temperature.The FSPCMs are generally brittle and have low mechanical strength,which cannot be directly utilized in thermal management of advanced electronic devices,human bodies,and many other applications.In addition,FSPCMs also suff er from low thermal conductivity properties.The multifunctional FSPCMs have remarkable capability of responsive to various energy sources such as light energy,electrical energy or magnetic energy,and convert these energy sources into thermal energy and release them in a timely manner,which is conducive to improving the utilization efficiency of PCMs.The multifunctional FSPCMs hold great promise for the fields of sensors,thermal therapy,wearable systems,and energy harvesting devices.Flexible FSPCMs can withstand certain deformations and contact more tightly with objects,which ultimately off ers great potential in a wide range of smart applications.The application of functional metal oxides in PCMs can integrate the thermal storage performance of PCMs with the high thermal conductivity and other functions of metal oxides.Considering this,two functional FSPCMs and flexible phase change coatings（FPCC）were prepared by nanoencapsulation technology,spraying method,and porous materials encapsulation technology in this thesis.The main contents and structures of this research are as described below:（1）Industrial paraffin wax（IPW）was employed as the core,cross-linked polystyrene（CLPS）as the supporting inner layer,and polypyrrole（PPy）as the functional outer layer to construct the photo and electric dual-responsive nanocapsules（IPW@CLPS@PPy）with high phase change enthalpy（△H_m=114.2 J/g）,excellent thermal stability,and efficient cyclability through a miniemulsion polymerization and rapid oxidation polymerization.The functional outer layer of PPy endows nanocapsules with excellent solar light absorption capacity and high electrical conductivity,resulting in ideal light-to-thermal conversion efficiency（88.4%）and electro-to-thermal conversion efficiency（80.1%）.Consequently,the synthesized nanocapsules have broad application prospects in light-to-thermal and electro-to-thermal conversion/storage fields.This research will not only give a new idea for the design and synthesis of multifunctional nanostructured form stable phase change thermal energy storage materials but also open up routes towards the development of FSPCMs for energy harvesting,conversion,and storage fields.（2）The FPCC was further fabricated by using the nanocapsules prepared in the second chapter together with polyurethane（PU）.The coating presents remarkable thermal energy storage performance（△H_m=88.4 J/g）,excellent thermal cycle stability,favorable light-to-thermal conversion ability,ideal flexibility,high durability,and shape adaptability.The light-to-thermal conversion efficiency can reach 76.2%at solar irradiation of 140 m W/cm²,and it remains stable even after 40 on/off cycles.Notably,the wearable thermal management device constructed by FPCC as a thermal management carrier possesses excellent light-responsive heating performance.The coating is promising for high-performance thermal management and making use of the heat generated by light to assist damage regional physical therapy.（3）High-quality three-dimensional flower-like and two-dimensional leaf-like nano Cu O were prepared through a facile one-step chemical precipitation method without surfactant at a relatively low temperature（80°C）.The three-dimensional flower-like Cu O-100 with large specific surface area and high porosity serves as a supporting material,followed by vacuum impregnation of polyethylene glycol（PEG）PCMs to obtain light-driven Cu O-100@PEG-80 FSPCMs with high thermal conductivity.The melting enthalpy（△H_m）and crystallization enthalpy（△H_s）of Cu O-100@PEG-80 are 159.7 J/g and 142.7 J/g,respectively,and the thermal conductivity reaches 0.52 W·m^-1·K^-1.In addition,the prepared FSPCMs exhibit exceptional light-to-thermal conversion ability,and the light-to-thermal conversion efficiency is as high as 91.6%at an irradiation intensity of 150 m W/cm²,which provides a solution for improving solar energy utilization efficiency.