Preparation And Properties Of Hollow Silica Nano-thermal Insulation Material

With the increasing demand for energy conservation and more and more attention to the energy crisis,it is important to develop materials with low thermal conductivity.Hollow structural materials（HSM）with unique hollow structure have huge application prospects in the field of thermal insulation.The high porosity of HSM can destroy the continuity of the heat transfer and convert the heat conduction into heat convection,which can effectively improve the thermal insulation of the material,thereby reducing energy consumption.HSM consisting of monodisperse hollow silica nanospheres（HSN）shows a promising potential for construction insulation due to its affordable cost and simple process.Aiming at the problems of low-yield,high energy consumption and non-ideal thermal conductivity of HSN,this paper studied from two aspects of process parameters and structural design.Polystyrene（PS）with the diameter of 140～575 nm was prepared by soap-free emulsion polymerization method as a sacrificial template for subsequent experiments.This research reported the best synthetic process for preparing HSN utilizing TEOS and Na₂Si O₃ as silica source,and compared its morphology and performance.The result indicated that the shell morphology of TEOS-based samples（HSN-T）was raspberry-like or smooth structure,the inner diameter was 120～310 nm and the shell thickness was 16～29 nm.The shell morphology of the Na₂Si O₃-based samples（HSN-N）was round honeycomb-like structure,the inner diameter was112～271 nm and the shell thickness were 10～15 nm.Solid connections existed between the spheres.The study compared the pore structure,yield,energy consumption and thermal properties of HSN-T and HSN-N.The BET surface area of HSN-T was 182.16 m2·g^-1 and the average yield reached 9.54%.The BET surface area of HSN-N was 766.25 m2·g^-1 and the average yield reached 93.75%,which was about 10 times higher that of TEOS-based samples.Hot Disk thermal constant analyzer results demonstrated that the thermal conductivity of the Na₂Si O₃-based samples was 0.0403～0.0610 W·m^-1·K^-1,lower than that of the TEOS-based samples with similar inner-diameter and shell thickness.The research confirms that the synthesis route with Na₂Si O₃ was a greener method which can solve the low yield and high energy consumption caused by using TEOS as a silica source.Furthermore,HSN incorporation into acrylate coatings can effectively reduce the thermal conductivity of the coating.By designing double layer hollow structure and adjusting different process parameters,yolk-shell structure and double-ring structure were successfully synthesized.The results indicated that the yolk-shell structure had petal-like morphology,the spacing of layer was20～290 nm.The relationship between core size and BET surface area was:32.61 m2·g^-1（100nm）>22.66 m2·g^-1（200 nm）>13.65 m2·g^-1（600 nm）.The double-ring hollow silica was prepared with HSN-T as a matrix and DVB as cross-linking agent.DVB can increase the degree of cross-linking of the polymer.The layer spacing were 18 nm and 35 nm.BET surface area were 59.81m2·g^-1and 61.63 m2·g^-1 respectively.The thermal conductivity of yolk-shell structure and double-ring structure tested by Hot Disk.The results confirmed that reducing the interlayer distance can effectively reduce the thermal conductivity of the material.The value of the double ring structure was as low as 0.0252 W·m^-1·K^-1,while the thermal conductivity value of the yolk-shell structure was slightly higher than the single layer structure due to the solid core.