Analyzing the Flow Drying Colloidal Suspensions Using Optical Coherence Tomography

In this work, we present the visualization and analysis of flow in drying colloidal suspensions composed of colloidal polymer particles in water. The flow induced particle transport and deposition can influence the final structure of the polymer film deposited. Employing time-lapse, high-speed imaging, Optical Coherence Tomography was used to monitor the dynamic process of drying colloidal droplets. With the aid of high refractive index tracer particles, fluid flows were captured. The speckle contrast analysis differentiates the dynamics of particles, showing the packing process and particle transporting to the edge of droplet. In low particle concentration suspension, this resembles the coffee ring phenomenon. In high concentrations of particles, a situation in practical coatings or ink-jet applications, the viscosity plays an important role in the material flow and deposition, resulting in different flow pattern and final dry film structures, such as cracks, shear bands, and skin formation.