Hydrostatic pressure measurement for evaluation of particle dispersion and flocculation in slurries containing temperature responsive polymers

The state of particle dispersion and flocculation was evaluated through hydrostatic pressure measurements in aqueous slurries of alumina with neutral and charged temperature responsive co-polymers of poly (N-isopropylacrylamide) (PNIPAM). Slurries were prepared and poured into test tubes at room temperature, and then heated in a hot water bath to a controlled temperature. The slurries were then cooled down to room temperature. The hydrostatic pressure at the bottom of the slurry was continuously measured. The effect of the fraction of charge on the polymer on the particle dispersion state was investigated by changing the ratio of acrylic acid (AA) to PNIPAM in the synthesized co-polymers. It was shown that the hydrostatic pressure of the slurry with 15% AA–PNIPAM co-polymer decreased the fastest at temperature above the polymer lower critical solution temperature (LCST), indicating that the largest flocs were formed due to a strong attractive force. However, the hydrostatic pressure of the 15% charged polymer did not recover (increase) after reducing the temperature below the LCST, revealing that the formed flocs did not re-disperse. On the other hand, the hydrostatic pressures of the slurries with 1% and 5% AA–PNIPAM co-polymer showed relatively quick decrease at temperature above the LCST and clearly recovered (increased) after changing the temperature to below LCST. The particles in these slurries can be changed from the dispersed to the flocculated state by temperature control. The hydrostatic pressure measurement has been shown to be a very useful tool to monitor how the particle dispersion and flocculation state are changed by changing the surrounding temperature for slurries with temperature responsive polymer.