Effects of water on the rheological properties of calcite suspensions in dioctylphthalate

Yield stress, storage and loss modulus of dispersions of colloidal particles of calcium carbonate in dioctylphthalate have been measured. They depend strongly on small amounts of water present in the suspension. The water thermodynamic activity has been used to characterise the water content of the suspension. There is an increase of more than an order of magnitude of the yield stress and storage modulus over the range 0.1–0.3 of water activity, and a smaller increase of the loss modulus. Beyond an activity of 0.3, these quantities are constant within experimental scatter. The effect of volume fraction has been investigated in this latter range of water activity. The results are discussed in term of interactions between particles.