A new material design combines phase separation and lithium bonding to create ionogels that are both strong and self-healing, enabling durable, flexible components for wearable electronics.
(Nanowerk Spotlight) Electronic materials are increasingly expected to do what skin does without effort: stretch, bend, recover, and repair themselves. As wearable devices move from rigid components to soft, body-integrated systems, materials that can survive the constant motion and impact of daily life are becoming essential. But matching mechanical toughness with flexibility and self-repair has proven unexpectedly difficult.
Most soft electronics either break under stress or slowly degrade because they cannot recover from minor damage. A crack in the wrong place, a strain across a fiber sensor, or a tear in a conductive patch can ruin an entire system.
Designing materials that are both strong and capable of healing themselves has emerged as a central challenge in wearable electronics, soft robotics, and biointegrated devices. The problem is not a lack of materials that are tough or self-healing. The difficulty lies in combining both properties in one system without compromise. Strong materials are often rigid and brittle. Self-healing ones tend to be soft and fragile. This trade-off has stalled progress in applications that demand both durability and autonomy.
Ionogels, a class of soft solids composed of polymer networks swollen with ionic liquids, have attracted attention for their flexibility, electrical conductivity, and compatibility with advanced manufacturing. These materials are promising candidates for next-generation fiber sensors, soft batteries, and wearable devices. But they too face the same core problem. Increasing their strength makes them less able to heal. Enhancing their self-repair capabilities reduces their mechanical integrity. This tension has limited their use in practical settings.
A recent study published in Advanced Materials (“Ionogels Reinforced by Ionophobic Coordination”) presents a new approach designed to overcome this trade-off. The researchers propose a method called Ionophobic Coordination Reinforcement (ICR), which combines two features: phase separation driven by polymer incompatibility with the ionic liquid, and reversible crosslinking enabled by lithium ion coordination.
This dual mechanism produces a material that is simultaneously strong, stretchable, and able to heal itself at room temperature. The work demonstrates that with careful control over molecular interactions and network structure, it is possible to achieve what has remained elusive: a high-performance ionogel that is both tough and autonomously repairable.
Design and properties of the ionogels. The material is made through a one-step UV-triggered polymerization process that combines different building blocks with an ionic liquid and lithium salt (a, b). The resulting gel is highly transparent, transmitting most visible light, which is useful for optical and electronic applications (c). Nuclear magnetic resonance measurements confirm hydrogen bonding between the polymer and the ionic liquid (d). Even after 24 hours at –20 °C, the ionogel remains elastic and can be stretched or twisted without breaking (e). (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
To build this material, the researchers synthesized a custom copolymer made from three monomers. Two of these are chemically compatible with ionic liquids. The third, N-isopropylacrylamide (NIPAM), is deliberately incompatible. When mixed with the hydrophobic ionic liquid [EMIM][TFSI], the NIPAM segments begin to separate, forming distinct hard regions within the otherwise soft material. This phase separation creates structural reinforcement.
At the same time, lithium ions introduced through the salt LiTFSI coordinate with carbonyl groups in the polymer. These interactions form physical crosslinks that are strong but reversible, allowing the network to hold together under stress while still enabling repair.
The resulting structure has two distinct thermal behaviors. One glass transition temperature appears at minus 60.27 degrees Celsius, where the soft phase remains mobile and flexible. The other occurs at 55.33 degrees Celsius, where the hard phase remains solid and reinforces the material. This combination allows the ionogel to stretch and move while resisting tearing, and to recover after being damaged.
The ICR strategy transforms the usual compromise between strength and healing into a cooperative system where each phase contributes to overall performance.
The authors fabricated the material through a one-pot photo-initiated polymerization process. When tested, the ICR ionogels showed a 6.4-fold increase in tensile strength, a fourfold increase in toughness, and a more than 35-fold increase in stiffness compared to controls without lithium ions. These gains were achieved while maintaining high optical transparency and flexibility, even at subzero temperatures. The material remained elastic and transparent after 24 hours at minus 20 degrees Celsius.
Spectroscopic measurements confirmed the molecular interactions responsible for this behavior. Nuclear magnetic resonance showed shifts consistent with hydrogen bonding and coordination between lithium ions and carbonyl groups. Infrared spectroscopy revealed changes in vibrational frequencies that matched the presence of physical crosslinks. Microscopy revealed bead-like microstructures that formed due to phase separation and were further stabilized by lithium ion coordination.
These findings were supported by simulations and X-ray photoelectron spectroscopy, which showed changes in electronic environments consistent with lithium complexation.
The mechanical properties were tunable. By adjusting the ratio of monomers, the researchers could shift the balance between the soft and hard phases. Increasing the amount of a soft-phase monomer made the material more stretchable but less strong. Lowering it increased strength but reduced elongation. The formulation called DNA0.5, which contained equal parts of the three monomers and 50 percent ionic liquid, achieved the best balance. Adding lithium ions to this formulation sharply increased all performance metrics.
Molecular dynamics simulations showed that lithium coordination lowered the system’s intermolecular energy, making it more stable.
The ionogels were tested not only for strength but also for self-healing. When cut and left to rejoin at room temperature, the material recovered more than 85 percent of its original mechanical strength within 48 hours. Electrical properties also recovered, allowing the material to restore conductivity after being broken. In one demonstration, a light-emitting diode powered by the ionogel turned off when the material was severed and turned back on after healing. These properties held up over time.
After nearly a month in ambient air, the material retained stable weight and function, even under varying humidity.
In addition to mechanical and healing performance, the material was shown to be compatible with melt processing. Rheological tests demonstrated that at 139 degrees Celsius, the ionogel reached a viscosity suitable for melt spinning. The researchers produced fibers by extruding the material at 155 degrees Celsius. These fibers had smooth surfaces, retained their mechanical properties, and showed enhanced performance compared to film counterparts. When used as humidity sensors, the fibers responded more quickly and sensitively than flat films due to their larger surface area.
The sensors were integrated into a wireless platform to detect respiratory moisture. The fiber-based sensors captured breathing patterns with high resolution. During exhalation, moisture decreased the material’s resistance; during inhalation, it rose. These resistance fluctuations produced clear signals for both normal and rapid breathing. The fiber sensors had a gauge factor more than four times higher than films, indicating superior sensitivity.
Even after being damaged and repaired, the sensors retained their function. They remained responsive after 27 days in ambient air and continued to perform under high humidity conditions.
The team also compared the use of other metal ions, including zinc, which can also form coordination bonds. Zinc ions improved mechanical strength but were less effective than lithium. The differences likely stem from the larger size and stronger binding nature of zinc, which restricts the dynamic movement needed for self-healing. Lithium, being small and more mobile, strikes a better balance between reinforcing the material and allowing it to reorganize at the molecular level.
By combining two seemingly incompatible design strategies—ionophobic phase separation and metal ion coordination—the ICR approach resolves a fundamental limitation in ionogel materials. It demonstrates that mechanical strength and self-healing are not mutually exclusive if the underlying structure is designed with precision.
The dual-phase architecture, dynamic bonding, and thermal tunability open the door to new applications in sensors, bioelectronics, and soft machines that need to survive and adapt under stress. Rather than choosing between strength and repair, materials built on this framework can offer both.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
