In situ monitoring of organic coating swelling by dynamic mechanical analysis and scanning electrochemical microscopy

Abstract

During hygrothermal ageing of organic coatings, the water uptake leads to a modification of barrier properties and to a possible swelling which is difficult to estimate. In this work, a DGEBA/DAMP polyepoxide resin with a thickness about 100 μm, completely cross-linked, was allowed to swell under two conditions: as free films and as coatings applied onto a metallic substrate. The swelling kinetics of the free films are in situ monitored using immersed dynamic mechanical analysis (DMA) tests, while the swelling kinetics of the coatings are estimated in situ by using the scanning electrochemical microscopy (SECM). It is shown that the maximum dimensional changes of the DGEBA/DAMP resin during the water absorption are about 5% for the coatings while they are only about 2% for the free films. This difference can be explained by the fact that, in the case of the coating, the metal substrate can constrain the polymer in the plane which affects the swelling upon water absorption by the relaxation of internal stresses developed during the curing process. We also mention the technical aspects when using SECM and DMA as convenient methods to evaluate the swelling.