Sol - Gel Prepared By Peg / Sio <sub> 2 </ Sub> Phase Change Materials

The surface temperature control is one of the main techniques at infrared stealth. The phase change materials can convert the heat or the solar energy to the latent heat and store them, so the surface temperature of the object will not change violently. In recent years, the phase change materials have a latent applied prospect in the field of the infrared stealthy materials, have already been paid attention to by people gradually. The common phase change materials will become the liquid at the solid–liquid phase change, and a container must be used to contain them, which will result in the inconvenience at the actual usage.In this thesis, polyethylene glycol (PEG) is the phase change material, silicon dioxide (SiO₂) derived from tetraethyl orthosilicate(TEOS) is the carrier, The PEG/SiO₂ composite form-stable phase change materials are prepared by Sol-Gel approach. The basic synthesis mechanisms of PEG/SiO₂ have been analyzed, the novel materials and process are explored and investigated. The main results are as follows:1. The new technics of production of the PEG/SiO₂ form-stable phase change materials by Sol-Gel approach is researched. In Sol-Gel reaction, TEOS is the forerunner, PEG1500, PEG2000, PEG4000, PEG6000, PEG10000 are the phase change materials, ethanol is the solvent, hydrochloric acid is the activator. The PH of the admixture is 1, the time of ripening is 4 hours, the temperature of ripening is 40℃, the time of ripening is not less than 24 hours, the temperature of desiccating is 80℃, the time of desiccating is not less than 3 days. Their most weight percentages of PEG with different molecular weight are 80%-83% in the PEG/SiO₂ form-stable phase change materials. PEG don't seep at 80℃after 24 hours. The phase change temperature is 47.58℃～63.26℃, and the phase change enthalpy is 73.70 J/g～131.3 J/g by DSC. the density is 1.220 g/cm3～1.301 g/cm3 by Specific Gravity Bottle method, the constant temperature is 38.9℃～51.8℃, the time of controlling temperature is 15～20 minutes by step cooling curve test. 2. The factors of affecting thermal properties of the PEG/SiO₂ form-stable phase change materials are studied in detail and the relative mechanisms are discussed. The phase change enthalpy and the phase change temperature of form-stable phase change materials increase with the molecular weight of PEG increasing by DSC, and are less than that of pure PEG. We analyze the causes of the changes by interpenetrate polymer net (IPN) and core-shell technology. The crystallization behavior of PEG in silica networks has been investigated by DSC and XRD.For Nano-silica confining the molecular chains of PEG, the long molecular chains can't enter freely crystalline domain, and crystal can't be regularly arranged, and crystal defects increase, and the degree of crystallization decreases, and the phase change enthalpy and the phase change temperature decrease. The remaining Si-OH and the SiO₂ adsorbing water and alcohol decrease PEG concentration in the PEG/SiO₂ form-stable phase change materials, which causes the phase change enthalpy decreasing.In this paper, we researched on the transition behavior of polymer PEG in nanostructured silica and the thermal properties of the PEG/SiO₂ form-stable phase change materials, its theory guidance to prepare nanopolymer PCM is significance.