Imaging of triboelectric charge distribution induced in polyimide film by using optical second-harmonic generation: Electronic charge distribution and dipole alignment

Abstract

By using an optical second-harmonic generation (SHG) microscope, we visualized spatial distribution of triboelectric charge in polyimide films, which are negatively charged by rubbing with a cotton belt. The origins of this triboelectric charging were excessive electronic charges and aligned dipoles. The excessive electronic charges were imaged using the probe laser wavelength of 1140 nm (SHG wavelength 570 nm), whereas the aligned dipoles were visualized by choosing the laser wavelength of 570 nm (SHG wavelength 285 nm). Combining the two visualized images showed that the dipolar alignment region with a width of 10 μm was induced on the rubbed polyimide surface, and at the same time, excess electronic charges were generated in that region. We conclude that dipolar alignment and electronic charging are main contributors, and the interaction between the two contributors plays an essential role in triboelectrification.