Preparation And Applications Of Multifunctional Composite Phase Change Materials Based On Emulsion-gel Template

In recent years,phase change materials（PCMs）-based latent heat storage technology has advanced quickly.Organic PCMs,such as paraffin,polyols,and fatty acids,have been widely used in intelligent thermal energy management systems because of their high latent heat,non-toxicity,and thermal stability.The leakage phenomena and low thermal conductivity of molten PCMs make them unsuitable for efficient heat storage and release.At the moment,the most common way for preventing leakage is to use encapsulation materials,such as porous materials,microcapsules,and polymer matrix.However,the inclusion of supporting materials will further inhibit the total thermal conductivity of the composite.To boost the thermal conductivity of the composite,thermal conductive fillers such as graphene nanoplates（GNPs）,boron nitride,and nanotubes must be added.But the heat storage capacity of composite phase change materials（CPCMs）declines as the thermal conductivity filler increases,making it critical to investigate an efficient thermal conductivity enhancement technology.In this thesis,a simple and universal strategy was designed to prepare multifunctional CPCMs by merging emulsion-gel template with oven drying technology.The emulsion-gel template inherited the benefits of both emulsion and gel.Thanks to the emulsifier methyl cellulose,the PCMs and GNPs were evenly dispersed in the emulsion first.And then the aqueous phase polymerized,realizing the immobilization of PCMs and GNPs.Finally,through the oven-drying technology,the internal shrinkage of emulsion hydrogel improved the encapsulation function and promoted the formation of heat conduction pathways.And the encapsulated multi-functional CPCMs were obtained.The underlying mechanisms in emulsion hydrogels during drying are detailed in this work,with the theories of capillary force and hydrogen bond rebuilding,which are supported by freeze drying contrast and solvent exchange method.The results showed that when the GNPs content was6 wt%,the thermal conductivity of the oven-dried CPCMs was 1.25 W m-1K-1,which was significantly higher than the thermal conductivity of the freeze-drying sample（0.54 W m-1K-1）,indicating that the thermal conductivity enhancement of oven-drying technology was efficient.The superiority of the oven-dried samples was also demonstrated by the compression strength.Although the samples’ Young’s modulus decreased with GNPs contents from 12.2 MPa to 8.3 MPa,they remained higher than that of the freeze-dried samples（7.8MPa to 4.4 MPa）.The shape stability test intuitively displayed that the CPCMs after freeze-drying completely lost packaging ability,but oven-dried CPCMs can maintain this performance.The CPCMs had a greater loading of PCMs（64wt% to 79 wt%）due to the removal of water,equating to a melting enthalpy of 171.5 J g-1 to 210.3J g-1.The thermal characteristics of CPCMs did not change significantly after 200 cycles of heating and cooling,exhibiting the excellent cyclic stability.Solar energy could be transformed into thermal energy and stored inside the materials when exposed to simulated solar irradiation,with a conversion efficiency of up to 96%.These findings suggest that in the realm of solar-thermal conversion,the oven-dried CPCMs demonstrate a promising application potential.