Displacement current generation across single monolayers of polyamic acids having pendant groups at the air-water interface

We investigated the reorganization of three kinds of monolayer polyamic acids, having different pendant groups (denoted PAA, AzOME and AzNO₂), on a water surface with measurements of the surface pressure-area (π-A) isotherms and the Maxwell displacement current. The three kinds of monolayers traced a similar π-A isotherm, indicating a similar conformational change on the water surface. For all three kinds of monolayer, some displacement current peak was generated during monolayer compression in the range before the initial rise of the surface pressure. The magnitude of the peak depended on the dipole moment of the pendant group ends incorporated in the polyamic acid monolayers. It was concluded that the current generation is due to the condensation of pendant group ends which stand up on the water subphase, and to monolayer compression.