Charge Transfer Happens Too Fast to See
Contact electrification results from the transfer of electrical charge between surfaces. Commonly associated with static electricity, it remains poorly understood. Now Felix Pertl of the Institute of Science and Technology Austria and his collaborators have discovered why that might be the case: The charge dynamics are too fast for some previous studies to be meaningful [1].
To map the charge on contact-electrified surfaces, researchers use Kelvin probe force microscopy (KPFM). The technique entails moving a tip across a surface without touching it and measuring the surface potential at each point. Pertl and his colleagues began their experiment with KPFM imaging of a square-centimeter polymer film. Next, they moved the film away from the microscope to sit beneath an actuator, which charged the surface by briefly pressing a polymer film onto it. Last, they returned the charged sample to its original position and reimaged its surface, all within 60 seconds. This record-fast switching was critical. The fact that static electricity dissipates is well known. Pertl and his colleagues found that the charge departed the surface on a timescale shorter than most KPFM scans.
The team’s data also showed that the deposited charge was largely uniform over the surface and that charge dissipation depends entirely on the material’s electrical conductivity. Models and experiments using different materials confirmed the idea that the better the insulator, the slower the charge dissipates.
Pertl says the results question the validity of static studies of charge transfer using KPFM on all but the best electrical insulators. The surface heterogeneity that was previously observed was likely not a feature of static electricity, as was claimed, but instead was an artifact of the inability to image the charge before it left.
–Rachel Berkowitz
Rachel Berkowitz is a Corresponding Editor for Physics Magazine based in Vancouver, Canada.
References
- F. Pertl et al., “No time for surface charge: How bulk conductivity hides charge patterns from Kelvin probe force microscopy in contact-electrified surfaces,” Phys. Rev. Lett. 135, 146202 (2025).