Ingress of water into organic coatings: Real-time monitoring of the capacitance and increase in mass

Water ingress into a cataphoretic coating employed in the car industry was studied using real-time mass and capacitance measurements. The results showed the presence of three well-differentiated time constants associated with the process. The corresponding time scales were 2–3 min, 1 and 10 h. The first time constant (fastest process) was assumed to be associated with the filling of surface pores by water. This process involved about 50% of the total water uptake. The second time constant was assumed to be due to the water occupancy of pores in the bulk of the coating. Finally, the slowest process was assumed to be due to water diffusion through the bulk coating. This process presented capacitive effects only if fillers were present in the coating.