Monitoring of film formation, curing and ageing of coatings by an ultrasonic reflection method

During film formation, curing and ageing of coatings changes in physical properties and chemistry of the material occur. For these processes, complex interactions of different factors have to be taken into account. In order to get a more detailed insight in mechanisms of film formation, curing and ageing, it is desired to monitor the changes of the mechanical properties in real time. Therefore, in this work various modifications of an ultrasonic reflection technique enabling such analyses are described.The ultrasonic method measures the complex acoustic reflection coefficient at the interface between a substrate and a coating for longitudinal and/or transversal waves at ultrasonic frequencies. From the complex acoustic reflection coefficients and the density of the sample, the corresponding mechanical moduli and the Poisson ratio can be calculated. The method can be considered as a real time dynamic mechanical analysis at high frequencies. Physical changes as vitrification, swelling and drying, crack initiation and delamination can be monitored. Recently, the ultrasonic reflection technique has been combined with near-infrared analysis for monitoring UV-induced curing reactions within seconds.