A light- and temperature-responsive hydrogel combines MXene and PNIPAM to achieve reversible, high-performance EMI shielding across a wide GHz range.
(Nanowerk Spotlight) The rapid growth of wireless communication technologies—from 5G networks to wearable electronics—has led to an increasingly dense electromagnetic (EM) environment. While EM waves are the foundation of high-speed connectivity, they can also interfere with the functioning of sensitive electronics, create privacy risks, and pose potential health concerns.
Traditional electromagnetic interference (EMI) shielding materials, such as metal foils or rigid composites, block these signals indiscriminately and are not easily adapted to changing operational needs or new device form factors. In flexible, mobile, and dynamic systems, these static solutions fall short. The development of materials that can actively and reversibly modulate their shielding properties is seen as a critical step toward adaptive electronics and secure, smart environments.
Efforts to create tunable shielding materials have focused on aerogels and hydrogels containing conductive fillers. Aerogels are lightweight and conductive but offer limited tunability due to the constraints of their static porous structures. Hydrogels—soft materials containing large amounts of water—introduce more flexibility. Their high water content allows for greater dielectric loss, which improves absorption of EM waves. Moreover, hydrogels can deform and change internal structure in response to external cues like temperature or pH.
Despite these advantages, many hydrogel-based systems still depend on mechanical contact or chemical exposure to change states, limiting their application in non-contact or remote-controlled settings. To overcome this, researchers have begun to explore non-contact activation methods, such as light and temperature, using materials that convert external energy into local heating.
One material that has attracted attention in this context is MXene, a class of two-dimensional transition metal carbides and nitrides. MXenes are known for their high electrical conductivity and strong photothermal response, meaning they can efficiently convert light into heat. When combined with thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM), which changes its hydration state near a critical temperature, this creates a promising platform for intelligent EMI shielding systems. These responsive systems could switch between shielding and transparent states based on environmental changes, such as sunlight exposure or device overheating, enabling applications in smart buildings, wearable technology, and electromagnetic safety systems.
In a study published in Advanced Science (“Stimuli‐Responsive MXene/PNIPAM Hydrogel WITH High‐Performance and Tunable Electromagnetic Interference Shielding Performance”), researchers at the Harbin Institute of Technology introduced a hydrogel-based material that combines PNIPAM with a conductive ink made from MXene and PEDOT:PSS, a conductive polymer blend. The composite is processed using an ice-templating method, which involves freezing the material to create a directionally aligned porous structure. This anisotropic architecture not only enhances mechanical strength but also accelerates the movement of water within the gel—a critical factor for fast and reversible switching of the material’s properties.
Schematic illustration of stimuli-responsive hydrogel. a) The schematic illustration of the hydrogel synthesis process. b) Schematic representation of PPM hydrogel with reversible characteristics, illustrating the transition between the EMI shielding and EM-wave-transparent states upon heating and cooling. (Image: Reprinted from DOI:10.1002/advs.202505551, CC BY) (click on image to enlarge)
At room temperature, the hydrogel is in a water-rich state, which allows it to shield electromagnetic radiation with high effectiveness. It can block more than 99.997% of incoming EM waves in the X-band (8.2–12.4 GHz), with a shielding effectiveness (SE) of approximately 59 dB. When heated above the lower critical solution temperature of PNIPAM (around 32°C), or exposed to light that is absorbed by MXene and converted to heat, the material undergoes a phase transition. Water is expelled from the hydrogel matrix, reducing the dielectric loss and thereby diminishing its EMI shielding performance. In this dry or aerogel state, the SE drops to about 2 dB, allowing EM waves to pass through. Importantly, this transition is reversible, and the original shielding capacity can be restored once the material reabsorbs water upon cooling.
The strength of the material lies not only in its high shielding performance and reversible behavior but also in its tunability. By adjusting the MXene content, hydrogel thickness, and light intensity, researchers can fine-tune the response range. For instance, increasing MXene concentration improves conductivity and enhances EM wave reflection. Adjusting the hydrogel thickness changes the amount of water available for dielectric loss, affecting overall performance. In experiments, the SE of the hydrogel could be modulated continuously from 59.3 dB to 15.5 dB in the X-band, with similar control observed in Ku- (12.4–18 GHz), K- (18–26.5 GHz), and Ka-band (26.5–40 GHz) frequencies.
A key aspect of the hydrogel’s performance is how it attenuates EM waves. This is achieved through a combination of mechanisms: reflection, where waves bounce off the material’s surface due to its conductivity; absorption, where energy is converted to heat by internal dipole movements and interface polarization; and scattering, where waves are deflected by internal structures, such as aligned pores, increasing their path length and interaction time within the material. Together, these mechanisms contribute to efficient dissipation of EM energy.
The researchers also investigated the influence of thickness on performance. Thicker hydrogels increase the shielding effectiveness because they contain more water and longer transmission paths, which enhance attenuation. However, they also become less efficient per unit of thickness. A 2 mm sample was found to provide the highest SE divided by thickness (SE/d), balancing material use and shielding performance effectively.
Mechanical testing confirmed the robustness of the hydrogel. It retained its shielding properties after 1,000 cycles of bending and stretching, and its tensile strength was significantly higher when the internal pore alignment was parallel to the stretching direction. The composite also showed a faster deswelling response than isotropic versions, indicating that the pore structure not only aids electromagnetic performance but also supports quick stimulus response.
To demonstrate practical applications, the team built a model room covered with the hydrogel. When exposed to electromagnetic radiation from a mobile phone, the hydrogel in its wet state reduced indoor radiation levels from 3331 μW/cm² to 85 μW/cm²—well below safety thresholds. Under light exposure, the hydrogel deswelled, and radiation levels rose again. Once the light was turned off, shielding resumed. Another application showed the hydrogel controlling wireless charging: when the device heated up during charging, the hydrogel interrupted the process by blocking the EM field, then resumed charging after cooling down. These demonstrations suggest the material could act as a passive safety mechanism in temperature-sensitive electronics.
The key innovation in this work is the dual responsiveness to light and temperature, allowing for remote, real-time control of EMI shielding across a wide frequency range. This is especially relevant for next-generation electronics that demand both flexibility and functional adaptability. The use of MXene, with its high photothermal efficiency and conductivity, in combination with a well-studied thermosensitive polymer, enables a level of tunability and reliability not previously achieved in soft shielding materials.
This hydrogel represents a step forward in developing intelligent electromagnetic shielding systems capable of reacting to environmental cues without the need for direct intervention. Its ability to reversibly switch states, respond quickly to changes, and maintain structural integrity under mechanical stress positions it well for integration into flexible electronics, wireless communication systems, and electromagnetic safety infrastructure. By enabling non-contact, reversible control over shielding behavior, this material opens new pathways for adaptable electromagnetic management in evolving technological landscapes.
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