We combined noninvasive ultrasonic and optical measurements to estimate the mechanical properties of forming colloidal films. Light reflection measurements determined the stage of drying and film structure. A concurrent ultrasound measurement quantified the film stiffness. The main finding was that compressing capillary forces induced a temporal peak in film stiffness when air began to enter the pores in the film. We believe that empirically observing such a stiffening event has not been reported before. This finding advances the understanding of the physics of consolidating suspensions.
Karppinen, T., Pajari, H., Haapalainen, J., Kassamakov, I., & Haggström, E. (2010). Concurrent structural and mechanical characterization of forming colloidal film by ultrasound and light. Applied Physics Letters, 96(17), . https://doi.org/10.1063/1.3387814