Young Gyu Jeong

Developing epoxy composites that simultaneously exhibit low dielectric response and high mechanical reliability remains challenging because conventional fiber reinforcement often increases interfacial polarization and dielectric permittivity. In this study, a multiscale hybrid architecture is designed by combining flat glass fibers (GF) with aramid nanofibers (ANF) as nanoscale interfacial modifiers. ANFs are prepared from aramid fibers through controlled deprotonation‐assisted fibrillation. Increasing the fibrillation time progressively refined the hierarchical fibrillar morphology, with the 72 h‐treated sample exhibiting the finest submicrometer structures while largely preserving the characteristic aramid chemical structure. The selected ANF and flat GF are incorporated into a diglycidyl ether of bisphenol A epoxy/amine system, followed by hot‐press curing. The flat GF provides primary load‐bearing reinforcement, while ANF incorporation is associated with changes in matrix/interfacial morphology, reduced segmental relaxation, and enhanced fracture‐energy dissipation. The best‐balanced composite containing 5 wt% GF and 0.5 wt% ANF exhibits a flexural strength of 170.72 MPa, flexural toughness of 1.45 MJ/m ³ , and impact strength of 4.58 kJ/m ² , corresponding to increases of 68.4%, 229.5%, and 103.6%, respectively, compared with neat epoxy. It also achieves a low relative permittivity of 2.34 and a dielectric loss of 0.0102 at 1 kHz. The enhanced mechanical–dielectric balance is consistent with the combined contributions of flat GF reinforcement, ANF‐induced matrix/interfacial modification, and changes in polymer segmental relaxation and dielectric polarization. These results demonstrate a multiscale design strategy for mechanically robust, low‐ k epoxy composites with potential for advanced electronic packaging and electrical insulation applications.

Carbon fiber (CF)‐reinforced epoxy composites are widely used in lightweight structural applications, but their performance is often limited by insufficient interfacial adhesion between the chemically inert CF surface and the epoxy matrix. In this study, a reactive multifunctional sizing system based on poly(acrylonitrile‐ co ‐glycidyl methacrylate) (PAG) and azide‐functionalized reduced graphene oxide (RGO‐N ₃ ) was developed to improve interfacial adhesion while retaining electrical functionality in the corresponding composite sizing films. PAG was synthesized by free‐radical copolymerization of acrylonitrile and glycidyl methacrylate, and RGO was functionalized with azide groups to improve its compatibility with the polymeric sizing matrix. Structural analyses confirmed the preservation of reactive glycidyl groups in PAG and the successful introduction of nitrogen‐containing functionalities onto RGO. SEM observation indicated a relatively uniform distribution of RGO‐N ₃ within the PAG sizing agent, with favorable coating morphology at intermediate filler contents. Microdroplet pull‐out testing showed that the interfacial shear strength increased from 7.6 ± 1.2 MPa for desized CFs to 18.7 ± 2.0 MPa for the composite containing 0.7 wt% RGO‐N ₃ , corresponding to an approximately 146% improvement. Post‐fracture SEM observations revealed increased epoxy retention on the fiber surface, indicating a transition from adhesive interfacial debonding to cohesive failure within the epoxy matrix. The enhanced interfacial performance is associated with the combined effects of possible PAG‐epoxy chemical interactions during curing, nitrogen‐containing surface functionalities, favorable graphene distribution, and improved stress transfer. This study demonstrates that integrating reactive polymer chemistry with functionalized graphene provides an effective strategy for engineering electrically functional and mechanically robust CF/epoxy interphases.

Metallic foil‐supported polymer composites that integrate enhanced thermal transport with absorption‐dominant electromagnetic interference (EMI) shielding are highly attractive for advanced electronic systems. In this study, asymmetric hybrid laminates composed of a thin aluminum (Al) foil and a thermotropic polyarylate/carbonyl iron particle (TP/CIP) composite layer were developed and systematically evaluated. The TP/CIP composites exhibited uniform filler dispersion, strong interfacial integrity, and preserved polymer matrix stability. Increasing CIP content enhanced the dielectric response and X‐band shielding effectiveness of the TP/CIP composites, resulting in a thickness‐normalized shielding effectiveness of ~18 dB/mm for TCIP80. Despite high filler loading, the composites maintained through‐thickness electrical insulation (10 ⁻¹¹ –10 ⁻⁸ S/cm) and demonstrated significantly improved thermal conductivity, increasing from 0.300 to 1.195 W/(m K) (~300% enhancement). Upon lamination with a 20 μm Al foil, the shielding behavior transitioned from reflection‐dominant to absorption‐dominant as the TP/CIP layer thickness increased. At TCIP80 layer thicknesses of 480 μm or greater, the absorption coefficient exceeded both 0.5 and the corresponding reflection coefficient. The optimized TCIP80‐960@Al laminate exhibited a total shielding effectiveness of ~54.9 dB, an absorption coefficient of ~0.73, and a reflection coefficient of ~0.27. This transition is attributed to reduced front‐surface reflection and enhanced electromagnetic attenuation within the TP/CIP layer. These findings establish thickness‐engineered TP/CIP‐on‐Al laminates as promising candidates for thermally conductive, electrically insulating, and absorption‐dominant EMI shielding in high‐frequency applications.

In this study, the effect of shellac (a natural polymer) on the stabilization behavior, porosity, and electrochemical performance of polyacrylonitrile (PAN)-based carbon nanowebs (CNWs) was investigated. Electrospun PAN/shellac precursor nanowebs were synthesized and subsequently converted into CNWs via sequential stabilization and carbonization. Physicochemical and electrochemical characterizations of the resulting material revealed that shellac incorporation increased oxygen-containing functional groups in the precursor, thereby reducing the stabilization enthalpy from 553.5 to 324.9 J g−1. Additionally, Brunauer–Emmett–Teller analysis revealed that shellac incorporation markedly increased the specific surface area (SSA) from 19.6 to 1553 m2 g−1. Correspondingly, galvanostatic charge–discharge measurements demonstrated an approximately 31.9% enhancement in specific capacitance, which increased from 126.05 to 166.27 F g−1 at a current density of 0.8 A g−1. These findings indicate that shellac effectively stabilizes precursors and promotes the in situ development of a porous carbon structure in PAN-based CNWs. Thus, shellac represents an effective natural additive for enhancing the SSA and electrochemical performance of PAN-derived carbon materials.

Styrene‐butadiene rubber (SBR) is widely used in tire and damping applications, yet its reinforcement with polar nanofillers is often limited by weak interfacial adhesion in nonpolar matrices. Here, electron‐beam (EB) curing is combined with glycidyl methacrylate (GMA) to promote interphase formation between non‐functionalized aramid nanofibers (ANFs) and SBR without prior ANF surface modification. ANFs were prepared via KOH/DMSO‐assisted fibrillation and incorporated into SBR using a masterbatch route, followed by compounding with GMA and EB irradiation. Process optimization shows that an EB dose of 150 kGy maximizes tensile strength despite monotonic increases in crosslink density with dose, indicating that excessive irradiation (200 kGy) causes over‐densification and/or chain scission that reduces extensibility and strength. FT‐IR evidences epoxy ring opening and consumption of GMA‐associated epoxy/vinyl features after EB curing, consistent with GMA‐mediated coupling at the ANF‐SBR interface. Swelling analysis reveals that crosslink density increases with ANF content only when GMA is present, implying the formation of interfacial networks. SEM fracture morphologies corroborate this interpretation: interfacial voids persist in SBR/ANF controls but largely vanish in SBR/GMA/ANF composites. Under optimized conditions (5 phr GMA, 150 kGy), tensile strength increases systematically with ANF loading, reaching a ~43% improvement at the highest ANF content investigated. Dynamic mechanical analysis shows a reduced tan δ at T _g , indicating restricted chain mobility associated with enhanced interfacial interactions and increased crosslink density.