New insights into the double layer structure from impedance measurements: Implications for biological systems

Abstract

Impedance measurements using a static mercury drop electrode in aqueous 0.01 M KCl, KBr and KI suggest structural effects of water and solute–solvent interactions near the double layer. The ion–dipole orientation effects are more dominant for chloride and least for iodide. These effects are more easily manifested at potentials near the changeover of the double layer structure. The interaction with mercury ions increases from chloride to bromide to iodide. For 0.01 M solutions, the double layer changeover potential shifts from about 0.15 to 0.025 to −0.15 V. Mott–Schottky plots show both p-type and n-type semi conduction. Also when the potential is varied from −0.5 to +0.5 V, unique differences in the nature of admittance, Nyquist plots and Bode plots are observed for the different halides. The sensitivity of the phase angle near the double layer changeover potential becomes less with bromide and least with iodide. This is consistent with the water structure formation and the breaking characteristics of these anions. Water structure-breaking effects increase from chloride to bromide to iodide. Our data suggest that frequency and potential dependent orientation changes of water molecules around ions and biological molecules play an important role in their electronic properties in living systems.