Polymer powder dissolution : wetting, dilution and shear

Powders of large molar mass are known to easily form lumps when poured in water: chocolate powder in cold milk, baby formula in water, polymer additives for drilling fluids,… to give a few examples. The powder dissolution process can be divided into two steps: (i) Wetting of the powder grains by water, and capillary penetration into the grain porosity; (ii) Swelling of the polymer by water down to a dilute aqueous solution of polymer.

In a first part, I will discuss the wetting dynamics of water on soluble polymer substrate that controls step (i). Second, I will identify the physical properties controlling the swelling of the gel layer that forms between the dry solid and the aqueous solution, and show how shear contributes to its erosion, giving scaling laws to describe step (ii).