Conductive Nanoparticle Hydrogel Blocks Electromagnetic Interference While Staying Soft and Stretchy

Electromagnetic interference has become one of the quiet hazards of modern life. As phones, medical monitors, aircraft avionics and countless other devices crowd the airwaves with signals, stray electromagnetic waves can degrade the accuracy of sensitive instruments, disrupt diagnoses in hospitals and even threaten flight safety. Engineers have long responded with rigid metal shields, but a growing body of research argues that the next generation of shielding should be flexible, wearable and even adhesive. A new study published in iScience takes a substantial step in that direction, describing a tough organic hydrogel laced with hybrid conductive nanoparticles that blocks more than 33 decibels of electromagnetic radiation in the commercially critical X-band while remaining soft, stretchy and sticky enough to wear on skin.

The material, developed by Zhi Lei, Daohai Zhang and colleagues, is built from two inexpensive and environmentally friendly ingredients: polyvinyl alcohol, a widely used water-soluble polymer, and gelatin, a natural biomass-derived protein. The researchers combined them into a semi-interpenetrating network in which the two polymer chains entangle during gelation and are further crosslinked by hydrogen bonds between abundant amino and hydroxyl groups. That molecular architecture produces a three-dimensional porous scaffold with high water content, and the same hydrophilic functional groups allow the gel to adhere to skin, paper, glass and metal through hydrogen bonding and intermolecular forces. Into this matrix the team dispersed composite nanoparticles made of carbon nanotubes decorated with ZIF-67, a cobalt-based metal-organic framework in which cobalt ions are coordinated by 2-methylimidazole ligands into a highly ordered porous crystal.

Each component of the hybrid filler plays a distinct role. Carbon nanotubes are lightweight and highly electrically conductive, so they raise the conductivity of the hydrogel dramatically, from 0.34 siemens per meter for the pristine polymer blend to 0.62 siemens per meter, an increase of 82.35 percent. ZIF-67, meanwhile, contributes cobalt centers that absorb electromagnetic waves, giving the composite dual loss mechanisms: dielectric loss from the conductive carbon network and magnetic loss from the cobalt ions. Together, the two phases dissipate incoming electromagnetic energy as heat rather than letting it pass through or bounce off. The porous hydrogel scaffold adds a third layer of defense, because its three-dimensional architecture provides anchoring sites for the nanoparticles and forces penetrating waves to undergo multiple internal reflections, each of which bleeds away more energy.

The synthesis relied on three complementary techniques. First, an in situ growth method deposited rhombic dodecahedral ZIF-67 crystals directly onto the surfaces of carboxylated multi-walled carbon nanotubes, with cobalt nitrate and nanotubes dispersed in methanol at controlled mass ratios and then added to a 2-methylimidazole solution under stirring for 24 hours. Second, a one-pot method dispersed the resulting CNTs@ZIF-67 particles uniformly into the aqueous PVA-gelatin precursor under ultrasonication. Third, cyclic freeze-thaw treatment physically crosslinked the polymers into a stable gel without any toxic chemical crosslinkers. Scanning electron microscopy confirmed that ZIF-67 had grown on the nanotubes and revealed how the fillers reshaped the gel’s internal pores.

Perhaps the most intriguing structural finding concerns electrostatics. When ZIF-67 alone was added, cobalt ions attracted electron-rich groups on the polymer chains, causing chain segments to bunch together and collapsing the gel’s three-dimensional network into a smoother, denser morphology. Carbon nanotubes alone infiltrated the pores and shrank them. But the combined CNTs@ZIF-67 particles produced hydrogels with more numerous and larger pores than either single filler. The researchers attribute this to an electrostatic confinement effect: oxygen anions on the nanotube surfaces neutralize the positive charge of the cobalt ions, weakening the electrostatic interactions between the composite and the polymer matrix and preserving the porous architecture that is so important for wave attenuation.

Spectroscopic analysis backed up the picture. X-ray diffraction peaks of the synthesized ZIF-67 matched the standard reference pattern at all expected crystal planes, indicating a complete lattice, while the hydrogels showed narrowed diffraction peaks consistent with grain-size changes induced by the cobalt-containing filler. Fourier transform infrared spectra showed no new functional groups after doping, meaning the nanoparticles disperse physically within the polymer framework rather than forming new chemical bonds. X-ray photoelectron spectroscopy, however, revealed subtle electronic interactions: the cobalt 2p binding energies shifted upward in the doped gels, suggesting that hydroxyl and carboxyl groups coordinate with cobalt ions and redistribute electron density at the interface.

Mechanically, the composite gel proved remarkably robust. The pristine PVA-gelatin hydrogel withstood compressive stresses of 18.75 megapascals at 71.07 percent strain; the shielding version reached 19.67 megapascals at 66.33 percent strain, with its compressive modulus rising from 38.1 to 41.8 kilopascals as the fillers constrained chain mobility and increased crosslinking density. A cylinder of the composite hydrogel just half a centimeter in diameter could lift a 200-gram weight without fracturing, and the material stayed firmly attached to paper, iron rods and glass rods for extended periods. Differential scanning calorimetry showed the additives did not disturb the gel’s crystallization behavior, and water content remained high at 88.99 percent, with water absorption of 265.92 percent, so the shielding function came without sacrificing the hydration and flexibility that make hydrogels attractive for wearables.

The electromagnetic results were the study’s centerpiece. Measured with a vector network analyzer across the X-band from 8.2 to 12.4 gigahertz, the plain hydrogel achieved an average shielding effectiveness of 14.70 decibels. The optimized composite, designated PGZC1, reached 33.32 plus or minus 1.67 decibels, a 126.7 percent improvement that comfortably exceeds the 20-decibel threshold generally considered effective shielding. Analysis of the reflection, absorption and transmission coefficients showed near-zero transmission and absorption dominating over reflection, confirming that the material neutralizes waves by soaking up their energy rather than bouncing them back toward other devices, a crucial distinction for crowded electronic environments. Conductivity of the optimized gel measured 0.512 plus or minus 0.026 siemens per meter.

Intriguingly, more nanotubes were not always better. When the researchers increased the carbon nanotube proportion in the CNTs@ZIF-67 filler, shielding effectiveness progressively declined. The explanation lies in agglomeration: nanotubes have enormous surface area and strong van der Waals attraction, so at higher loadings they clump together, disrupting the synergistic interplay between the carbon and the ZIF-67 phase and damaging the gel’s porous structure, which reduces the surface area and active sites available for wave scattering. The finding underscores a recurring lesson in composite design, that uniform dispersion at modest loadings can outperform brute-force addition of conductive filler.

The researchers propose a clear shielding mechanism that ties the observations together. The PVA-gelatin network forms the structural scaffold, while well-dispersed CNTs@ZIF-67 particles build a conductive network and help generate relatively independent, complete spherical pores. When a wave strikes the surface, part is reflected and part penetrates, losing energy as it crosses the conductive walls; reflected components bounce between wall layers, attenuating further with each pass. Because absorption dominates, the energy ultimately dissipates as heat within the material. The authors suggest the gel’s combination of high shielding, toughness, adhesion, water retention and processability positions it for flexible electronics, wearable devices and stretchable sensors, offering a green, low-cost route to protecting both devices and people from the electromagnetic clutter of modern technology.

Subject of Research: CNTs@ZIF-67 composite nanoparticles enhancing electromagnetic interference shielding in tough PVA-gelatin organic hydrogels

Article Title: CNTs@ZIF-67 conductive composite nanoparticles enhance the electromagnetic shielding performance of tough organic hydrogels

Article References: Lei, Z., Zhang, D., Hu, Y., Zhou, T., Diao, K., Liu, D., Song, A., Zou, K., & Qin, S. (2026). CNTs@ZIF-67 conductive composite nanoparticles enhance the electromagnetic shielding performance of tough organic hydrogels. iScience, 29(11), Article 114635. https://doi.org/10.1016/j.isci.2026.114635

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.114635

Keywords: electromagnetic interference shielding, hydrogel, carbon nanotubes, ZIF-67, metal-organic framework, polyvinyl alcohol, gelatin, X-band, wearable electronics, dielectric loss, magnetic loss, conductive composites