The research, led by Yingying Zhao, Shengchang Zhang, Qibin Xu, Mengjin Jiang, and Pengqing Liu of the College of Polymer Science and Engineering at Sichuan University, together with Krishnan Jayaraman of the University of Auckland, tackles a problem that has stubbornly resisted experimental analysis. At the boundary where a basalt fiber meets a polymer matrix, several factors operate simultaneously: the chemical groups grafted onto the fiber surface, the nanoscale roughness of that surface, and the way resin molecules arrange themselves in response. In a real composite, all of these effects are entangled. Measure the strength of an interface and you cannot easily tell whether the credit belongs to chemical bonding, to mechanical interlocking, or to something subtler still. The Sichuan University team’s solution was to decouple these influences using atomistic simulations, allowing each factor to be varied and evaluated in isolation.

Central to the study is a workhorse of composite chemistry: the silane coupling agent known as gamma-aminopropyl triethoxysilane, or KH550. Coupling agents are molecular intermediaries, molecules designed with one end that bonds to an inorganic surface and another that is compatible with organic polymers. KH550 carries amino groups, which are rich in nitrogen and hydrogen atoms capable of forming hydrogen bonds with surrounding resin chains. Using computational simulations, the researchers showed that KH550 does something rather elegant on the basalt fiber surface: it balances highly positive and highly negative electrostatic regions, creating multiple binding sites where resin molecules can attach. In effect, the coupling agent transforms a chemically patchy surface into a welcoming landscape for polymer chains.

The quantitative results are striking. At the interface between basalt fiber and polyamide 66, a common engineering thermoplastic, KH550 modification increased the number of hydrogen bonds by 10.4 percent. More tellingly, the interfacial interaction energy, a measure of how strongly the two phases attract each other, became more negative, shifting from -384.4 to -487.9 kilocalories per mole. In the language of molecular simulation, a more negative interaction energy means a more stable, more tightly bound interface. That single modification, applied at the molecular scale, produced a measurable and substantial strengthening of the chemical handshake between fiber and resin.

But chemistry alone was only half the story, and this is where the study’s decoupling approach proves its worth. The researchers examined three different composite systems: basalt fiber with polyamide 66, basalt fiber with epoxy resin, and basalt fiber with polypropylene. Across these systems, they separated the contributions of KH550’s amino groups from the contributions of surface morphology, the atomic-scale texture of the fiber surface. The verdict was consistent: the chemical interactions provided by the amino groups contributed more to interfacial mechanical enhancement than surface morphology did. At the basalt fiber and polyamide 66 interface specifically, introducing amino groups enhanced the interfacial mechanical response by a factor of 1.49, while modifying the atomic-scale morphology enhanced it by a factor of 1.29. Both matter, but chemistry leads.

Perhaps the most intriguing finding concerns how surface texture influences the resin itself. The simulations revealed that for both the polyamide 66 and epoxy systems, atomic-level surface morphology regulates the arrangement, or conformation, of resin molecular chains, and that this effect optimizes mechanical properties more effectively than larger surface asperities that simply allow resin to infiltrate surface irregularities. In other words, the classical picture of mechanical interlocking, where rough surfaces grip the polymer like microscopic Velcro, is not the dominant mechanism at these scales. Instead, the fine texture of the surface shapes how polymer chains fold and orient, and those conformations determine how load is transferred across the interface.

KH550 also orchestrates a dramatic reorganization of the resin. According to the simulations, the coupling agent transforms resin molecular chains from conformations that lie aligned along the fiber surface into interpenetrating structures that reach into the matrix. The researchers attribute this to two combined effects: enhanced interaction between the amino groups and the resin, and steric hindrance, the physical crowding that prevents chains from lying flat against the surface. The result is a molecularly interlocked interphase, a region where fiber and polymer are no longer simply touching but genuinely entangled at the chain level.

To connect these molecular pictures to measurable mechanics, the team performed atomic-scale nanoindentation simulations, a computational analogue of the classic hardness test in which a sharp tip presses into a material to probe its resistance to deformation. The results revealed a fundamental shift in how the material fails. In unmodified interfaces, the resin deformed by sliding along the interface, a mode that ultimately leads to adhesive failure, where the bond between fiber and matrix simply gives way. After KH550 modification, deformation was redirected into the bulk of the matrix itself, a transition that shifts failure from adhesive to cohesive. Cohesive failure, in which the polymer itself must tear rather than the bond peeling apart, is generally the more desirable mode because it means the interface is no longer the weakest link. The maximum indentation force rose from approximately 2.9 to 4.0 nanonewtons, a roughly 38 percent increase attributable to the molecular redesign of the interphase.

The significance of this work extends well beyond basalt fiber. Fiber-reinforced composites of every kind, from glass and carbon to natural fibers, depend on the same delicate interfacial chemistry, and designers have traditionally improved interfaces by trial and error, testing coupling agents and surface treatments empirically. By rigorously separating the roles of chemical functionality, atomic-scale morphology, and resin conformation, the study provides something rarer: a mechanistic roadmap for rational interphase design. It tells engineers which lever to pull first. If chemistry contributes more than texture, then investment in tailored coupling agents and surface functionalization should take priority over aggressive roughening treatments, and the choice of coupling agent should be matched to the electrostatic and hydrogen-bonding character of the specific resin.

There are also practical implications for sustainability and materials selection. Basalt fiber is produced from abundant volcanic rock without the energy-intensive precursor chemistry required for carbon fiber, and it is compatible with a range of resins, from commodity polypropylene to high-performance epoxies and polyamides. The finding that the same coupling agent strategy strengthens interfaces across polyamide 66, epoxy, and polypropylene systems suggests a versatile design principle that could accelerate the adoption of basalt composites in automotive parts, wind turbine components, construction materials, and consumer products. As the authors note, the research clarifies the intrinsic interfacial strengthening mechanism and provides guidance for rational interphase design. What was once an opaque tangle of competing effects is now a decoupled, quantified, and ultimately engineerable set of levers, and that clarity may prove to be the most valuable property of all.

Subject of Research: Interfacial strengthening mechanisms in basalt fiber-reinforced polymer composites

Article Title: Decoupling of factors influencing interface characteristics in basalt fiber-reinforced polymer composites

Article References: Zhao, Y., Zhang, S., Xu, Q., Jayaraman, K., Jiang, M., & Liu, P. (2026). Decoupling of factors influencing interface characteristics in basalt fiber-reinforced polymer composites. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02118-6

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02118-6

Keywords: basalt fiber, polymer composites, silane coupling agent, KH550, interface, hydrogen bonds, molecular simulation, nanoindentation, polyamide 66, epoxy resin, interphase design, surface morphology

The work, published in the Journal of Materials Science by Enyi He, Bo Song and colleagues at Huazhong University of Science and Technology and China Three Gorges University, centers on FeCoCrNiAl2, a five-element high-entropy alloy. Unlike conventional alloys built around a single dominant metal, high-entropy alloys mix several elements in roughly equal proportions, producing chaotic, distorted crystal lattices with unusual electronic and magnetic properties. In recent years these materials have attracted intense interest for electromagnetic applications precisely because that atomic disorder scatters and dissipates energy in ways ordinary alloys cannot.

But the alloy alone was not enough. The researchers combined it with reduced graphene oxide, or rGO, the defect-rich, electrically conductive form of graphene that has become a staple of microwave-absorption research. The critical variable turned out to be the ratio. When the mass ratio of FeCoCrNiAl2 to rGO was set at 3:1, the composite delivered its best performance, a balance the authors attribute to the synergistic interplay between the alloy’s magnetic losses and the graphene’s dielectric losses. Too much graphene and the material becomes overly conductive, reflecting waves at its surface instead of letting them in; too little and the dielectric loss pathway is starved.

The architecture is as important as the chemistry. Using a microemulsion technique, the team built spherical particles in which ethyl cellulose forms the outer shell framework and epoxy resin fills the inner core. The resulting microspheres are hollow and riddled with pores, and that internal void space does real electromagnetic work. Every boundary between air, polymer, alloy and graphene is a dielectric-magnetic heterointerface, a place where the material’s electrical and magnetic response changes abruptly. At each such boundary, incident microwaves are partially reflected, partially transmitted and partially absorbed, so a single wave entering a microsphere can bounce and scatter many times before it escapes, losing energy at every encounter.

The numbers reported in the study are striking. At a sample thickness of just 2 millimeters, the composite achieves an effective absorption bandwidth of 3.6 gigahertz, spanning 10.8 to 14.4 gigahertz, right in the heart of the X and Ku bands where military radars and satellite links operate. At a thinner 1.5 millimeters, the material reaches a minimum reflection loss of minus 40.48 decibels at 17.08 gigahertz. In practical terms, a reflection loss of minus 40 decibels means that more than 99.99 percent of the incident microwave energy at that frequency is absorbed rather than bounced back, which is the figure of merit that matters most for radar evasion and electromagnetic interference control.

Perhaps the most useful property is tunability. By simply varying the sample thickness between 1 and 5 millimeters, the composite can be adjusted to absorb efficiently anywhere across a broad range from 3.8 to 18 gigahertz, essentially covering the entire C, X and Ku bands. Thin absorbers typically struggle at lower frequencies because the quarter-wavelength matching condition demands thicker samples, so a material that can be tuned across nearly three octaves of radar spectrum by thickness alone gives designers a single filler that can serve many roles in one platform.

Underlying all of this is a cascade of dissipation mechanisms working in parallel. The researchers identify dipole and interfacial polarization, conductive loss, natural and exchange ferromagnetic resonance, and eddy current loss as the contributors. Dipole polarization arises when bound charges in the defective graphene and polymer matrix lag behind an oscillating field. Interfacial polarization, the Maxwell-Wagner-Sillars effect familiar from composite dielectrics, accumulates charge at the heterointerfaces created by the hollow porous structure. On the magnetic side, the iron- and cobalt-rich alloy undergoes natural ferromagnetic resonance, while exchange coupling between neighboring magnetic moments and eddy currents induced by the alternating field add further channels through which electromagnetic energy is converted into heat.

Impedance matching is the quiet hero of the story. An absorber fails if its surface impedance differs too much from that of free space, because the wave reflects before it ever penetrates the material. The hollow, porous architecture and the deliberate blending of magnetic alloy with dielectric graphene tune the composite’s permittivity and permeability into a regime where waves enter readily and are then dissipated inside. The abundant interfaces improve that matching while simultaneously multiplying the internal reflection pathways, which is why the authors credit the microspherical design, not just the constituent materials, for the enhanced performance.

The choice of ethyl cellulose and epoxy also carries practical weight. Both polymers are well established in microencapsulation technology, from controlled-release pharmaceuticals to self-healing coatings, and previous work has shown that polymer microcapsules filled with carbonyl iron or other functional powders can be incorporated into structural composites. A microwave absorber built from such microspheres could in principle be blended into resins, coatings or even 3D-printing feedstocks, and several of the authors have previously explored graphene and carbonyl iron microspheres for additive-manufactured absorbing composites. That processing heritage suggests a plausible route from laboratory measurement to real-world radomes, drone skins and electronics enclosures.

The broader context is a fast-moving field. High-entropy materials, from alloys to diborides and carbides, are being systematically explored for wave absorption, with recent studies reporting broadband performance at extreme temperatures and low-frequency absorption through engineered exchange interactions. Graphene-based hybrids with ferrites, carbonyl iron and molybdenum disulfide have pushed reflection losses deeper and bandwidths wider for a decade. What distinguishes the new work is the combination of a high-entropy magnetic filler, a two-dimensional conductive filler and a hollow polymer-templated architecture in a single lightweight particle, with each element contributing a distinct loss mechanism. The researchers, funded by the State Key Laboratory of Materials Processing and Die and Mould Technology, describe their strategy as a new route toward high-performance, wideband electromagnetic absorbers. If the fabrication scales beyond the laboratory, materials like these could quietly become the skin of the next generation of stealthy aircraft, satellites and electronic devices, absorbing the very signals that would otherwise give them away.

Subject of Research: Microwave absorption properties of FeCoCrNiAl2-rGO high-entropy alloy and graphene composite microspheres

Article Title: Fabrication and enhanced microwave absorption properties of high-performance FeCoCrNiAl2-rGO composite materials

Article References: Fabrication and enhanced microwave absorption properties of high-performance FeCoCrNiAl2-rGO composite materials. (n.d.). https://doi.org/10.1007/s10853-026-13276-9

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13276-9

Keywords: high-entropy alloy, reduced graphene oxide, microwave absorption, FeCoCrNiAl2, composite microspheres, impedance matching, radar stealth, electromagnetic interference, ethyl cellulose, epoxy resin, dielectric loss, magnetic loss

The stakes are considerable. The United States Department of Energy has set technical targets for bipolar plates ahead of anticipated fuel cell stack commercialization by 2030, demanding an in-plane electrical conductivity above 100 siemens per centimeter, a flexural strength above 40 megapascals, and robust chemical resistance, processability, and long-term reliability. Meeting all of those requirements simultaneously has proven difficult. Metallic plates offer strength and easy machining but corrode without expensive surface treatments. Pure graphite plates conduct beautifully and resist chemicals, yet they are brittle and hard to form into the thin, intricate shapes that modern stack designs demand. Resin-based carbon composites, which blend moldable polymer with conductive graphite fillers, have emerged as a compelling middle path, but their performance depends exquisitely on the microstructure that forms during fabrication.

Researchers led by Seon Ho Lee and Song Mi Lee of Chungnam National University and the Korea Institute of Energy Research attacked the problem from three directions at once: the loading of multi-walled carbon nanotubes, the particle size of the graphite filler, and the mixing method used to combine everything with epoxy resin. Carbon nanotubes are the stars of the conductive composite world. Roughly 20 nanometers in diameter and up to 50 micrometers long, they possess extraordinary intrinsic conductivity and tensile strength, and they readily form interconnected electron highways through a material. But they carry a notorious flaw. Strong van der Waals attractions between their nonpolar surfaces cause them to clump into agglomerates, and those clumps act as defects rather than reinforcements, degrading both the electrical and mechanical performance of the finished composite.

The team’s solution was elegantly practical. In the conventional dry mixing route, graphite and nanotubes are simply stirred into the resin, leaving stubborn clumps intact. In the wet mixing route, the epoxy resin, curing agent, and accelerator are first dissolved in acetone, and the graphite and nanotubes are then blended into this dilute solution before the solvent is removed by rotary evaporation and oven drying. The dilution gives each nanotube room to unbundle and allows the resin to coat the graphite particles uniformly. When the coated powders were hot-pressed into plates at 160 to 200 degrees Celsius, the difference was visible to the naked eye. Dry-mixed samples collapsed at low molding pressures of 20 megapascals, while wet-mixed counterparts held their shape, and at 60 megapascals both routes produced dense, mirror-smooth surfaces. Quantitatively, wet mixing delivered 15 to 25 percent higher flexural strength at every pressure tested, a benefit the authors attribute to fewer microvoids and better mechanical continuity.

Scanning electron microscopy revealed exactly why the solvent makes such a difference. In cross-sections of dry-mixed composites, nanotubes sit in obvious clumps on the graphite surfaces, blocking resin infiltration and weakening the bonds between particles. In wet-mixed samples, the nanotubes are spread evenly along the interfaces between graphite grains, where they can do their intended job: bridging gaps, transferring stress, and stitching together a continuous conductive network. The images also showed that adding 7 weight percent nanotubes fills the voids between graphite particles with conductive bridges, explaining the sharp gains in conductivity and strength relative to nanotube-free plates.

Graphite particle size turned out to be the other decisive variable. The researchers compared a fine synthetic graphite with particles around 6 to 7 micrometers against a coarser grade reaching 48 to 65 micrometers. Counterintuitively, the coarse graphite won on nearly every electrical metric. Larger particles provide broader contact areas with their neighbors, so electrons hop more easily from grain to grain, and the wider interparticle spaces give well-dispersed nanotubes room to span the gaps. Composites built on large graphite particles consistently showed higher density, higher conductivity, and lower interfacial contact resistance than their fine-particle counterparts, although the finer particles offered a slight hardness advantage at low nanotube loadings, where the sheer number of particle contact points matters more.

The optimum formulation, labeled W-LG-CNT7 for wet mixing, large graphite, and 7 weight percent nanotubes, proved to be a genuine sweet spot. Its electrical conductivity reached 151.6 siemens per centimeter, comfortably beating the Department of Energy target of 100. Its flexural strength hit 56.7 megapascals, well above the 40 megapascal requirement, and its interfacial contact resistance measured just 4.6 milliohm square centimeters, far below the 10 milliohm square centimeter benchmark and better than the 8 to 12 milliohm square centimeters typical of commercial SIGRACELL graphite plates. Push the nanotube content to 9 weight percent, however, and everything deteriorates. The excess nanotubes re-agglomerate, creating resistive dead zones and microvoids that undermine both electron transport and mechanical bonding. More is not better; well-dispersed and just enough is better.

Durability testing delivered perhaps the most commercially significant result. Bipolar plates in a working fuel cell are exposed to phosphoric acid that leaches from the membrane electrode assembly, so the team immersed their samples in 95 percent phosphoric acid for 1,000 hours to simulate years of operation. Every composite lost less than 15 percent of its flexural strength, but the optimized wet-mixed plate lost only 8.2 percent, its dense, well-coated microstructure effectively blocking acid and moisture penetration. That kind of chemical resilience, combined with the corrosion immunity that composites enjoy over metals, addresses one of the last major obstacles to long-life fuel cell stacks.

The ultimate proof came in a real single-cell fuel cell test. The researchers assembled a 25 square centimeter cell with a Nafion membrane, platinum catalysts, and carbon paper gas diffusion layers, operated it at 70 degrees Celsius on humidified hydrogen and oxygen, and swept the current to map its performance. The optimized bipolar plate delivered a stable open-circuit voltage of about 0.97 volts and a peak power density of 0.86 watts per square centimeter, more than 30 percent higher than an identical cell built with a nanotube-free plate. The gains were most pronounced at high current densities between 1.0 and 1.6 amperes per square centimeter, precisely the region where internal resistance losses normally throttle a stack, confirming that the nanotube network was genuinely improving electron transfer under load.

What makes this study resonate beyond the laboratory is its message about manufacturing. No exotic materials were invented; the breakthrough lies in a solvent, a particle size, and a dosage. As hydrogen economies scale up worldwide, such process-level refinements, cheap to implement in existing compression-molding lines, may matter as much as catalyst breakthroughs. A bipolar plate that is stronger, more conductive, more acid-resistant, and demonstrably capable in a working cell brings the 2030 commercialization horizon measurably closer, one well-stirred batch of acetone and nanotubes at a time.

Subject of Research: Optimization of carbon nanotube loading, graphite particle size, and wet mixing for carbon composite bipolar plates in proton exchange membrane fuel cells

Article Title: Enhanced mechanical and electrical properties of carbon composite bipolar plates in PEMFCs via wet mixing and CNT optimization

Article References: Lee, S. H., Lee, S. M., Park, S., Jung, D.-H., Song, W.-J., & Lee, Y.-S. (2025). Enhanced mechanical and electrical properties of carbon composite bipolar plates in PEMFCs via wet mixing and CNT optimization. Advances in Industrial and Engineering Chemistry, 1(1), Article 27. https://doi.org/10.1007/s44405-025-00020-1

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00020-1

Keywords: bipolar plates, PEMFC, carbon nanotubes, wet mixing, graphite composites, epoxy resin, electrical conductivity, flexural strength, interfacial contact resistance, fuel cell durability, hydrogen energy, compression molding