Effects of interface bonding on the macro-mechanical properties of microcapsule/epoxy resin composites

Microencapsulated phase change materials (MPCMs) can be used as energy-saving fillers to regulate the temporal and spatial mismatches of thermal energy in many fields. However, the MPCMs/epoxy composites suffer from severe mechanical strength reduction due to the poor interface bonding between microcapsules and epoxy matrix. The present work aims to enhance the microcapsule/epoxy interface mechanical properties to improve the macro tensile strength of composites via chemical modification of the microcapsules. Three silane coupling agents (SCAs) were used to modify the outer surface of n-octadecane@MF microcapsules to introduce covalent bonds at the microcapsule/epoxy interface. Surface modification has little effect on the rupture strengths of individual microcapsules, whereas nanoindentation mapping reveals that the γ-(2, 3-epoxypropoxy) propytrimethoxysilane (EPTMS) modified microcapsule/epoxy interface has enhanced elastic modulus of 4.20±0.08 GPa and nanoindentation hardness of 0.24±0.01 GPa, which are markedly higher than the elastic modulus (3.78±0.18 GPa) and nanoindentation hardness (0.20±0.02 GPa) of matrix. The EPTMS modified microcapsule/epoxy composites exhibit 23.55% higher tensile strength than the unmodified microcapsule/epoxy composites. It demonstrates that enhancing the microcapsule/epoxy interfacial mechanical properties with appropriate SCAs is beneficial to improving the macro tensile strength of the composites.