Correlation between the ion permeation and free volume property in ethyl cellulose film during the acid treatment
Ethyl cellulose can be applied as an erasable barrier coating. The microstructure of the coating is a key factor that influences the anti-corrosion property. In order to investigate the correlation between the hole structure and the acid treatment time, the microstructure of the ethyl cellulose immersing in acid for different time was evaluated. Scanning electron microscopy (SEM) showed holes around 100 nm enlarged in the samples immersed for longer time. Electrochemical impedance spectroscopy (EIS) implied the film resistance decreased, while positron annihilation lifetime measurement indicated the free-volume holes enlarged with increasing immersing time. All the results are in agreement with each other. A model has been proposed to explain the film resistance, that the film resistance is inversely proportional to the cross-sectional area of pores for ion permeation. The experimental data confirmed that free-volume holes acting as the tunnels for ions permeating through the EC film. It would be a potential method to evaluate the tortuosity of holes in membrane that coupling the membrane resistance with free-volume hole size.