Heat-treated PAN Fiber Mats Enable Flexible Temperature and Pressure Sensing at High Temperatures

By Akshatha ChandrashekarReviewed by Susha Cheriyedath, M.Sc.Oct 2 2026

By tuning how PAN fibers conduct electricity and respond to compression, researchers built a flexible sensing platform designed to track heat and contact pressure under demanding conditions.

Paper: An integrated polyacrylonitrile fiber mat sensor for simultaneous temperature and pressure monitoring in high-temperature environments. AI-generated abstract conceptual image created using ChatGPT/OpenAI

A recent study in Microsystems & Nanoengineering reports a flexible polyacrylonitrile (PAN) fiber mat sensor that simultaneously monitors temperature and pressure in high-temperature environments. The researchers tune PAN's electrical properties through controlled heat treatment or laser processing. This processing enables the material to support separate thermoresistive temperature-sensing and piezoresistive pressure-sensing elements with independent readout.

Engineering PAN fibers for multimodal high-temperature sensing

Flexible sensors could enable electronic skin, wearable systems, industrial monitoring, and robotic platforms operating under demanding conditions. But most flexible pressure sensors work at room temperature. Thermal changes can alter their electrical response and interfere with pressure measurements. Repeated mechanical loading can degrade the sensing structure and reduce long-term reliability.

The study addresses these challenges by using PAN fiber mats as a multifunctional sensing material. The researchers control the material’s electrical properties through laser processing or thermal treatment. These treatments can convert PAN from an electrically insulating polymer into a conductive material. The pressure element maintained stable responses during repeated mechanical loading.

Controlling structure and conductivity through thermal treatment

The team prepared PAN fiber mats from acrylonitrile, adding methyl acrylate and methyl methacrylate to improve the precursor solution's spinnability. After spinning, washing, stretching, and drying, they subjected the fibers to controlled thermal treatment. The study examined treatment temperatures from 600 to 1100 °C to determine how thermal conversion affected the material’s morphology, composition, mechanical properties, and sensing behavior.

Thermal treatment caused a marked change in electrical conductivity. PAN remained electrically insulating at lower treatment temperatures, while its resistivity decreased substantially between 600 and 1000 °C. At 1100 °C, the fiber structure was severely damaged, and elemental analysis indicated that the PAN fibers had oxidized and volatilized. At treatment temperatures above 1100 °C, the material became insulating again. Microscopy showed that samples treated below 1000 °C largely retained their interconnected fibrous morphology. The porous structure contained spaces between fibers and particles that could change during compression.

We attributed the electrical transition to a series of heat-driven reactions, including cyclization, dehydrogenation, denitrogenation, and aromatization of PAN. These reactions first convert PAN into a ladder-like polymer and then produce increasingly extensive sp² carbon networks. Raman spectroscopy supported this structural evolution, with the D-to-G peak area ratio decreasing from 1.71 to 1.01 as treatment temperature increased.

For device fabrication, the researchers used polyimide as the flexible substrate because of its thermal resistance and flexibility. They deposited metal interdigitated electrodes using conventional microfabrication processes and attached the PAN sensing elements with high-temperature ceramic adhesive.

Balancing porosity, conductivity and mechanical response

The results showed that thermal treatment strongly influenced the mechanical response of the PAN fiber mats. Under a 25 N load, untreated PAN deformed by about 0.4 mm, while the 1000 °C-treated sample deformed by about 0.7 mm. This indicates that increasing treatment temperature reduces the fiber mat's elastic modulus, with the effect becoming more pronounced above 800 °C.

This structural change directly affected pressure sensitivity. The PAN mat treated at 700 °C showed the highest pressure sensitivity across 0–480 kPa. Its relatively loose fibrous structure allowed additional conductive contact points to form as pressure increased. The material reached a pressure sensitivity of 0.78 kPa^-¹.

The 700 °C-treated material produced a maximum output current of 59.3 μA at 480 kPa at room temperature. The researchers selected the 700 °C treatment condition for the pressure-sensing element. The 700 °C-treated PAN material also showed a strong temperature-dependent electrical response. Its current changed systematically with temperature from room temperature to 432 °C. In stability tests, the authors monitored the material continuously below 300 °C. At 300 °C, the authors reported measurable current drift, while cyclic tests produced a repeatability error of ±3.91%. At temperatures above 180 °C and pressures above 150 kPa, simultaneous loading caused the mat to lose structural integrity and reduced the rate of current change.

The pressure sensor showed strong mechanical durability. After 10,000 loading–unloading cycles at 150 kPa, the pressure-response attenuation remained below 1%. The repeatability error remained below 0.96%. At room temperature and 100 kPa, the sensor responded to pressure within 53.2 ms and recovered within 8.8 ms. The response time reached 105.3 ms at 100 °C and 113.6 ms at 200 °C when temperature and pressure were applied simultaneously.

The team demonstrated array fabrication using laser processing. An 8 × 8 pressure-sensor array contained 64 sensing units within a 90 × 90 mm area. The directly laser-processed array distinguished different pressure loads. A second array, made from laser-cut units that were then thermally treated, recognized letter-shaped pressure patterns corresponding to "X", "J", "T", and "U". Laser etching also produced temperature-sensing structures with different geometries and support configurations.

Toward reliable multimodal sensing in extreme environments

The study demonstrates that controlled thermal conversion can transform polyacrylonitrile (PAN) fiber mats into flexible materials for simultaneous temperature and pressure sensing. Researchers used separate PAN elements for the thermoresistive and piezoresistive measurements within a flexible sensing platform. The selected pressure sensor covered a 0–480 kPa range and maintained stable performance over 10,000 loading–unloading cycles. The temperature sensor operated from 25 to 300 °C with a 0.1 °C resolution. These are the individual sensing ranges; the paper does not demonstrate every temperature-pressure combination across both full ranges.

The results show a trade-off between conductivity and structural properties: higher thermal-treatment temperatures improved conductivity up to about 1000 °C but reduced pressure sensitivity and mechanical stiffness, while treatment at 1100 °C severely damaged the PAN fibers. Mounted on robotic grippers, the sensors measured objects at different temperatures and pressures, and the temperature element supplied information used to separate the two signals. The authors identify lithium-ion battery thermal management, industrial equipment condition monitoring, and emergency rescue as possible application areas.

The laser-processing strategy produced multi-unit pressure arrays and patterned temperature-sensing structures on flexible substrates. This work shows how tunable PAN properties, porous fiber architecture, and adaptable laser processing can enable high-temperature multimodal sensing.

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