Joseph Jiang's PhD dissertation defense: Physics in Osmotic Pressure Gradients
Channel: Joseph Jiang
Date: 2022-04-20

During drying, colloids undergo solidification and maintain concentration and osmotic gradients at the drying front. In colloids comprising two particle sizes, relative motion of the two different sized particles are observed by fluorescence confocal microscopy. Analysis of the time-lapse images reveals two prominent phenomena in drying colloidal suspensions: (1) large particles migrate against the osmotic pressure gradient established by the small particles; and (2) when the large particles are oil droplets, they also deform with an axial symmetry but not the front-back symmetry. A model based on diffusiophoresis describes the first phenomenon; and the force balance between the anisotropic surface stress of the oil droplets (Laplace pressure) and the osmotic pressure of the accumulated small particles surrounding the droplets does the second.