Unveiling the influence of asphalt on the thermal storage behavior of microencapsulated phase change materials through non-isothermal crystallization kinetics

Abstract

The melting and crystallization of phase change materials (PCM) are crucial processes for their functionality. Understanding their kinetic behavior is significant for guiding material design and promoting applications. This work analyzes the thermal storage kinetics of three systems—paraffin, hybridized microencapsulated phase change materials (HMPCM), and modified asphalt with HMPCMs (HMA)—under varying heating/cooling rates, temperatures, times, and environmental conditions. The effectiveness of HMPCMs in regulating the temperature of asphalt is also validated. The temperature regulation results indicate that the maximum temperature difference between the HMA and the matrix asphalt can reach 8.4 °C, demonstrating good temperature control effectiveness. Results from the non-isothermal crystallization kinetics reveal that HMPCMs provide heterogeneous nucleation sites for paraffin, thereby promoting its nucleation. However, HMPCMs also restrict the growth region of paraffin molecular chains, hindering crystal growth. Additionally, asphalt significantly impedes the nucleation and crystal growth of paraffin. The mechanism by which asphalt hinders paraffin crystal growth can be explained through the interfacial thermal resistance effect. The differences in material properties between asphalt and HMPCMs decrease the thermal conductivity at the two-phase interface, reducing heat transfer efficiency. This leads to a decrease in paraffin crystallization efficiency and lowers the liquid–solid phase transition temperature, ultimately delaying paraffin crystallization. Results on crystallization activation energy imply that encapsulating paraffin and incorporating it into asphalt diminish the mobility of paraffin molecules, which ultimately results in a reduction of the melting/crystallization enthalpy of the phase change material.