Multiscale hybridization and chemical bonding create ultra-durable flexible strain sensors

Researchers in China have developed a new approach to enhance the durability of wearable strain sensors by integrating carbon nanotubes (CNTs) with styrene–butadiene rubber (SBR). These sensors, which are crucial for applications in health monitoring and industrial safety, often suffer from reduced accuracy due to repeated stretching and exposure to harsh environments. The innovative design aims to maintain sensor performance under such demanding conditions.

The new material leverages the electrical conductivity of CNTs, which are embedded within the elastic SBR polymer. This combination allows the sensor to detect mechanical changes by measuring variations in electrical resistance as the material deforms. However, a key challenge is preventing CNTs from clustering due to van der Waals forces, which can impair sensor sensitivity and reliability.

To address this, the research team employed a dual strategy involving filler hybridization and interfacial chemical bonding. Silica was grown on the CNT surfaces using tetraethyl orthosilicate (TEOS), creating a hybrid filler with a conductive core and an active inorganic shell. This modification improves CNT dispersion within the rubber matrix.

Further, the team used a silane coupling agent, KH590, to attach thiol groups to the modified filler. During the vulcanization of the SBR matrix, these groups form covalent bonds with the rubber, stabilizing the conductive network and reducing the likelihood of sensor degradation over time.

This chemically bonded architecture enhances the sensor's mechanical resilience by distributing stress more evenly and minimizing the Payne effect, which is the reduction in stiffness under strain. As a result, the sensors demonstrated stable performance through over 15,000 tensile cycles and maintained functionality in harsh chemical environments.

The findings suggest that this approach could be valuable for developing flexible sensors with high sensitivity and durability, suitable for health-monitoring systems and industrial applications. While challenges remain in manufacturing and biocompatibility, the study highlights the potential of chemical bonding in improving the reliability of wearable electronics.