Hexagonal Boron Nitride‐Decorated Hollow Glass Microsphere/Epoxy Composites With Enhanced Interface Stability for Lightweight Acoustic Matching Layers

ABSTRACT Hollow glass microsphere/epoxy (HGM/EP) composites are lightweight polymer composites for acoustic matching layers, but the smooth microsphere surface has weak compatibility with epoxy, causing interfacial gaps, aggregation, and unstable acoustic transmission. In this study, hexagonal boron nitride‐decorated hollow glass microspheres (HGM@BN) were prepared through hydroxylation, amination, and electrostatic self‐assembly, and then incorporated into epoxy resin. The modification was intended to regulate the filler–matrix interface rather than only adjust acoustic impedance. Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy confirmed the stepwise surface modification and the attachment of boron nitride nanosheets onto the microsphere surface. Compared with pristine HGM/EP, the optimized HGM@BN‐5/EP composite showed fewer interfacial defects, a longitudinal sound velocity of 2210 m s −1 , an acoustic impedance of 1.35 MRayl, an increase in glass transition temperature from 84°C to 105°C, and an increase in compressive strength from 78 to 120 MPa. When used as a matching layer in approximately 200 kHz air‐coupled ultrasonic transducers, HGM@BN‐5/EP increased echo peak‐to‐peak amplitude by about 60% and reduced maximum relative center‐frequency drift from 6.0% to 2.7% over −20°C to 70°C. Gas‐flow and wind‐speed sensing tests further verified its functional acoustic value. These results show that HGM@BN offers an effective interface‐regulation route for lightweight epoxy‐based acoustic matching composites.