Dispersion and flow characteristics of hardshell microcapsules with phase change materials.

To investigate the sedimentation and flow characteristics of hard-shell microcapsule/water slurries, the apparent viscosity, apparent dispersion volume fractions, and friction characteristics were measured. The hard-shell microcapsule contains disodium hydrogen phosphate hydrate as a phase change material. Poly (vinyl alcohol) (PVA) with a concentration from 0 to 2,000 ppm was applied as a dispersant. A dragreducing surfactant system was also added to the slurries to improve the flow characteristics of the slurries. As a drag-reducing surfactant, oleylbishydroxyethylmethylammonium chloride was added at 2,000 ppm with a counter-ion of sodium salicylate. As a trial, the concentration of microcapsules was set at a low value at 1 or 2 wt%. From the results, severe adsorption of surfactants onto the hard-shell microcapsules was found. Then, no drag reduction or sedimentation prevention occurred in the cases without PVA. However, there is a weak sedimentation prevention effect and effective drag reduction effect when PVA is present. Thus, it is concluded that the desorption of surfactants from the microcapsules occurs and forms a synergetic structure with the PVA.