Concurrent structural and mechanical characterization of forming colloidal film by ultrasound and light

Abstract

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.

Imaging stress and strain in the fracture of drying colloidal films

“…26,[29][30][31][32][33] Alternatively, Man and Russel 34 used a unique setup to measure the critical pore pressure for cracking by pushing solvent out of a colloidal lm under controlled pressure to initiate cracks. Karppinen et al 35 used noninvasive ultrasonic and optical instruments to measure the capillary stress and estimate the high-frequency mechanical properties of colloidal lms at different drying stages. These results provide information on the average stress inside a lm, which correlates well with the drying and fracturing events, but are limited due to the intrinsic heterogeneity of drying colloidal lms.…”