Toughening Epoxy Resin Using a Liquid Crystalline Elastomer for Versatile Application

As typical anisotropic materials combining the entropy elasticity of an elastomer with the self-organization of rigid mesogens, liquid crystalline elastomers (LCEs) possess the emerging applications as an ideal toughener that can maximally balance the comprehensive properties of the blended epoxy resins (EP). Herein, an LCE named poly[4,4'-bis(6-hydroxyhexyloxy)-biphenyl phenylsuccinate] (PBDPS) was utilized to construct robust EP thermosets with optimal toughening efficiency and anomalous reinforcement by controlling over the formation of multiscale phase structures in the matrix over broad sizes ranging from nano- to micron-scale while increasing the content of PBDPS. The results revealed that the thermoset displaying a nanoscaled phase separation effectively enhanced the tensile strength of EP by 20.7% with barely less than 1.0 wt % of PBDPS, whereas the thermoset containing 11.1 wt % of PBDPS displayed typical submicron-scaled phase-separated structures and showed the highest impact strength (3-fold of the neat EP) and fracture toughness (improved by 85.0%). The micron-scaled phase separation was induced with further increase of the PBDPS content, whereas the toughening efficiency slightly decreased and the tensile strength sharply deteriorated. The diverse morphology and its interfacial adhesion with the matrix were proposed to account for the variation of mechanical properties. The improved toughness and strength did not come at the cost of other properties, thermal stability, and glass transition temperature (T-g), and modulus of the toughed EP thermosets were mainly maintained. This work provided a fruitful attempt for designing robust EP thermosets and suggested attractive potential application in many fields.