Investigation On Optical Absorption Properties Of Core-shell Nanoparticles And Arrays And Its Temperature Profiles In A Phase Change Media

Core-shell nanospheres could be widely used in many industrial applications including nonlinear optics,photo-chemical transformation and nanosensing.Some typical composite nanospheres(with Si or Si C core and Au,Ag,Cu or Al shell)are numerically investigated for the LSPR effect existing at the particle surfaces on the thermal and optical properties.The results show that the position of the absorption peak of the core-shell nanoparticles will be shifted due to the influence of particle shape,structure,size and materials,from comparison we can see that the core-shell nanoparticles have different properties from single nanoparticles,and the absorption peaks were more flexible to modify.In addition to the above factors,the spatial distribution of the nanoparticle arrays also plays an important role in changing the absorption peak.Phase change material(PCM)can be used for thermal storage,and efficient storage of thermal energy can be achieved using phase transitions between solid and liquid.Common phase change materials(PCM)include organic,inorganic and eutectic materials,paraffin and salt hydrates are typical PCM.The incorporation of nanoparticles with different sizes and different materials into the phase change material can improve the solar energy absorption efficiency,and so enhance the heat capacity efficiency of the phase change material,which can make the phase change material get higher heat storage at the lower storage temperature.In this paper,the optical absorption properties of the core-shell nanoparticles and the arrays and its temperature profiles were investigated by using the finite-difference time-domain(FDTD)method.The first chapter introduces the research background and significance of the thesis,and the current research situation at home and abroad.In the second chapter,we introduce the concept of Mie scattering theory,the derivation of scattering coefficient,the absorption efficiency factor and scattering efficiency factor.Then we introduce the FDTD method,including Maxwell equations,discrete difference equations,numerical stability and PML boundary layer and periodic boundary.In Chapter 3,the absorption properties of single-component nanosphere and nanocylinder,core-shell nanosphere and nanocylinder as well as core-shell nanosphere and nanocylinder arrays with different metal shells,different inner and outer radii and different structures are analyzed,its spectral absorption under different conditions are calculated.In chapter 4,the absorption properties of nanosphere and core-shell nanospheres in a phase change media are calculated.The characteristics of the particle temperature are also analyzed.The work of this paper lays the foundation for improving the optical absorption properties of nanoparticles and improving the efficiency of photo-thermal conversion and improving the energy storage characteristics of phase change materials through structural optimization.