A simple voltage pulse causes unmodified carbon microfibers to bend and recover, revealing unexpected actuation behaviour at microscopic scale.
Researchers at the Institute of Physical Chemistry, Polish Academy of Sciences (IChF) have developed a method to control the motion of pristine carbon microfibers using electricity. The proof-of-concept study, published in Nature Communications, shows that unmodified carbon fibers can bend and return to their original position through asymmetric electrochemical processes, opening new possibilities in micromechanics and soft robotics.
Manipulating fibres as thin as, or thinner than, a human hair has long been a technical challenge. While many “smart” materials can respond to stimuli such as light, heat or pH, microfibers often require coatings or structural modifications to achieve controlled motion. The IChF team demonstrated that bare carbon fibres, without additional functionalization, can act as miniaturized actuators.
The researchers placed a single carbon fibre with micrometre-scale diameter inside a closed bipolar electrochemical cell. In this setup, oxidation occurs at one end of the fibre and reduction at the other, even without direct electrical wiring. The team compared smooth fibres with naturally rough ones that exhibit asymmetric pore distributions. When voltage is applied in an electrolyte containing lithium and perchlorate ions with a benzoquinone/hydroquinone redox couple, ions insert into the fibre surface unevenly.
This asymmetric ion insertion generates uneven mechanical stress, causing the rough fibre to bend. When the voltage is reduced, ions exit the structure, and the fibre straightens. The motion is reversible and can be tuned by adjusting the applied voltage, pulse duration and fibre length. Cyclic voltage pulses enable repeated bending and straightening, effectively allowing the fibre to function like microscopic tweezers.
Dr. Wojciech Nogala, Research Associate at Institute of Physical Chemistry, Polish Academy of Sciences who led the study, says, “Our findings may open up intriguing possibilities for actuators based on prefabricated asymmetric carbon fibres,” as the approach enables wireless actuation and could support the development of microactuators for applications ranging from synthetic muscles in microbotics to precise manipulation in miniaturized systems.