Conductive nanofibers have emerged as a transformative material for flexible sensors and smart textiles, offering a unique combination of electrical conductivity, mechanical flexibility, and high surface area. Among the various materials explored, carbonized polyacrylonitrile (PAN) nanofibers stand out due to their tunable conductivity, structural stability, and compatibility with scalable fabrication methods like electrospinning. These fibers enable the development of lightweight, wearable, and responsive systems without relying on traditional rigid electronic components.
The production of conductive PAN-based nanofibers typically begins with electrospinning a PAN precursor solution, followed by stabilization and carbonization at high temperatures. Electrospinning parameters such as voltage, flow rate, and collector distance influence fiber diameter and morphology, which in turn affect conductivity and mechanical properties. For instance, fibers with diameters ranging from 100 to 500 nm exhibit optimal balance between flexibility and electrical performance. Carbonization temperatures between 800°C and 1200°C yield conductivities in the range of 1 to 100 S/cm, suitable for sensor applications. Higher temperatures increase graphitization, enhancing conductivity but may reduce flexibility due to increased brittleness.
Flexible sensors leveraging carbonized PAN nanofibers capitalize on their piezoresistive or capacitive response to mechanical stimuli. When integrated into textiles or elastomeric substrates, these fibers detect strain, pressure, or bending through measurable changes in electrical resistance. For example, a strain sensor fabricated with carbonized PAN nanofibers can achieve gauge factors between 5 and 50, depending on fiber alignment and substrate adhesion. Such sensors demonstrate high durability, with some studies reporting over 10,000 cycles of repeated stretching without significant performance degradation.
In wearable applications, conductive nanofibers enable seamless integration into fabrics for health monitoring or human-machine interfaces. Textile-based sensors woven with carbonized PAN fibers can detect physiological signals like respiration, pulse, or joint movement. The high porosity of nanofiber mats also ensures breathability, a critical factor for comfort in wearable devices. Additionally, their lightweight nature avoids the bulkiness associated with conventional metal-based conductive threads.
Beyond strain sensing, conductive nanofibers serve as active elements in touch or pressure sensors. Layered architectures combining insulating and conductive nanofiber mats create capacitive sensors responsive to localized pressure. These systems exhibit sensitivity thresholds as low as 1 kPa, making them suitable for applications like prosthetic skin or ergonomic monitoring. The large surface area of nanofibers further enhances sensitivity by increasing contact points under deformation.
Challenges remain in optimizing the interfacial adhesion between carbonized nanofibers and polymeric substrates to prevent delamination during repeated use. Surface modifications, such as plasma treatment or chemical functionalization, improve bonding while preserving conductivity. Another consideration is environmental stability; hydrophobic coatings may be applied to mitigate moisture absorption, which can alter electrical properties.
Future directions include hybrid systems where carbonized PAN nanofibers are combined with other conductive materials like silver nanowires or conductive polymers to enhance performance. For instance, a bilayer design with a conductive polymer coating on carbonized fibers could improve stretchability without compromising sensitivity. Advances in large-scale electrospinning and roll-to-roll processing will also be crucial for commercial adoption.
In summary, conductive nanofibers derived from carbonized PAN offer a versatile platform for flexible sensors and smart textiles. Their tunable electrical and mechanical properties, coupled with scalable fabrication, position them as key enablers of next-generation wearable technologies. Continued refinement in material processing and integration techniques will expand their applicability across healthcare, robotics, and interactive textiles.