Binary Co-Gelator Strategy: Toward Highly Deformable Ionic Conductors for Wearable Ionoskins

Novel Polymer Gel Lubricant Functionalized with a Phosphate Anion for Friction Reduction and Film Thickness Enhancement in Multiple Lubrication Conditions

In this study, a supramolecular polymer gelator functionalized with a phosphate anion, PMUS-P, has been successfully synthesized through radical polymerization, and its physicochemical, rheological properties and tribological performance were carefully evaluated as a gel lubricant formed through non-covalent self-assembly in 500SN base oil. The results showed that the gel has a dense network structure, providing excellent stability and mechanical strength. Additionally, the PMUS-P gel exhibits good shear-thinning behavior and excellent creep recovery, effectively avoiding the volatility of lubricants. Under a steel-steel contact, the PMUS-P gel showed excellent tribological performance in long-term wear tests and a high-load, high-frequency, or high-temperature condition. For instance, in long wear tests, the 15 wt % PMUS-P gel showed a 44.90% reduction in average coefficient of friction (COF) compared to 500SN base oil, along with an 88.05% decrease in wear. The lubrication mechanism study revealed that the chemical reactive film formed by friction played a key role in reducing friction and wear, preventing the friction pairs from direct contact. In terms of film-forming properties, the PMUS-P gel demonstrates superior lubrication performance in comparison to 500SN base oil, achieving higher film thickness. Given these advantages, the PMUS-P gel has significant potential for prolonging machinery service life and reducing operational energy consumption, promising to become a new high-performance lubricant.

Advances in ionogels for proton-exchange membranes

To ensure the long-term performance of proton-exchange membrane fuel cells (PEMFCs), proton-exchange membranes (PEMs) have stringent requirements at high temperatures and humidities, as they may lose proton carriers. This issue poses a serious challenge to maintaining their proton conductivity and mechanical performance throughout their service life. Ionogels are ionic liquids (ILs) hybridized with another component (such as organic, inorganic, or organic-inorganic hybrid skeleton). This design is used to maintain the desirable properties of ILs (negligible vapor pressure, thermal stability, and non-flammability), as well as a high ionic conductivity and wide electrochemical stability window with low outflow. Ionogels have opened new routes for designing solid-electrolyte membranes, especially PEMs. This paper reviews recent research progress of ionogels in proton-exchange membranes, focusing on their electrochemical properties and proton transport mechanisms.

Super tough and high adhesive eutectic ionogels enabled by high-density hydrogen bond network

Ionogels have attracted tremendous interest for flexible electronics due to their excellent deformability, conductivity, and environmental stability. However, most ionogels suffer from low strength and poor toughness, which limit their practical applications. This article presents a strategy for fabricating ionogels with high toughness by constructing high-density hydrogen bonds within their microstructure. The ionogels exhibit a maximum fracture strength of 11.44 MPa, and can sustain a fracture strain of 506%. They also demonstrate a fracture energy of 27.29 MJ m-3 and offer a wide range of mechanical property adjustments (fracture stress from 0.3 to 11.44 MPa, fracture strain from 506% to 1050%). Strain sensors assembled with ionogels demonstrate exceptional sensing performance and enable motion detection of human joints. This study provides a new approach for achieving strong and tough ionogel design used for high-performance flexible electronic applications.

Multimodal Wearable Ionoskins Enabling Independent Recognition of External Stimuli Without Crosstalk

Wearable ionoskins are one of the representative examples of the many useful applications offered by deformable stimuli-responsive sensory platforms. Herein, ionotronic thermo-mechano-multimodal response sensors are proposed, which can independently detect changes in temperature and mechanical stimuli without crosstalk. For this purpose, mechanically robust, thermo-responsive ion gels composed of poly(styrene-ran-n-butyl methacrylate) (PS-r-PnBMA, copolymer gelator) and 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMI][TFSI], ionic liquid) are prepared. The optical transmittance change arising from the lower critical solution temperature (LCST) phenomenon between PnBMA and [BMI][TFSI] is exploited to track the external temperature, creating a new concept of the temperature coefficient of transmittance (TCT). The TCT of this system (-11.5% °C-1 ) is observed to be more sensitive to temperature fluctuations than the conventional metric of temperature coefficient of resistance. The tailoring molecular characteristics of gelators selectively improved the mechanical robustness of the gel, providing an additional application opportunity for strain sensors. This functional sensory platform, which is attached to a robot finger, can successfully detect thermal and mechanical environmental changes through variations in the optical (transmittance) and electrical (resistance) properties of the ion gel, respectively, indicating the high practicality of on-skin multimodal wearable sensors.