Selective Distribution of Silica Nanoparticles in Epoxy/Thermoplastic Blends and Its Impact on Mechanical Properties

ABSTRACT As one of the most widely used thermosetting resins, performance optimization of epoxy (EP) resin has consistently been a key research focus. EP/thermoplastic (TP)‐nanoparticle systems have attracted attention for their potential synergistic effects on polymer properties. However, the mechanical performance is not expected due to unclear mechanisms governing nanoparticle distribution. In this study, the dual‐phase structures formed between epoxy and different thermoplastic resin were firstly compared and then the selective distribution behavior of nanoparticles in EP/TP blend under various curing conditions and surface characteristics, as well as the effect on dynamic mechanical properties and hardness, were investigated. Based on the research results, the EP/Polyetherimide (PEI) blend was selected for subsequent investigation of selective distribution behavior of nanoparticles because of large‐scale dual‐phase structure and the inapparent secondary phase separation. Hydrophilic nano‐SiO 2 preferentially localized in the EP phase under high‐temperature curing (120°C/1 h + 160°C/4 h), driven by thermodynamic effect, while lipophilic KH‐550‐modified nano‐SiO 2 migrated to the PEI phase. Lower curing temperatures (100°C/10 h) induced kinetic dominance, redistributing modified nano‐SiO 2 into the EP phase and altering phase morphology to a sea‐island structure. Dynamic mechanical analysis demonstrated that local agglomeration effect of nanoparticles in one phase reduced storage modulus and glass transition temperature (), with EP/PEI‐SiO 2 ‐KH550 exhibiting a reduction. Conversely, hardness increased by 22.5% for EP/PEI‐SiO 2 ‐KH550 due to dense nanoparticle clusters in the PEI phase. These findings highlight important roles of curing conditions and surface modifications in tailoring nanoparticle distribution in EP/TP blends, providing valuable information for the unexpected mechanical properties and more efficient strategies.