Two Independent Measurements of Debye Le

This study investigates the Debye lengths in doped nonpolar liquids, focusing on heptane doped with varying concentrations of poly(isobutylene succinimide) (PIBS). The objective was to determine the Debye lengths and confirm these measurements through independent methods. We performed electric current measurements between parallel-plate electrodes separated by 1.2 mm in a PIBS solution, utilizing the rapid initial charging of the capacitor to infer the dielectric constant and observing the slower decay of current due to electrode polarization. By employing the Gouy-Chapman model, we deduced Debye lengths ranging from 80 to 600 nm, which decreased with increasing PIBS concentration. These findings were corroborated by additional experiments measuring double-layer repulsion using total internal reflection microscopy, which indicated that the charge carriers are likely inverted PIBS micelles with Stokes diameters of 20 to 40 nm. Furthermore, dynamic light scattering revealed a size distribution with an intensity-averaged diameter of 15 nm. This approach simplifies the process of determining Debye lengths and ionic strengths compared to force measurements, emphasizing the significance of charge carrier mobility in conductivity assessments.