Effect of Water on Nano-rheology of Dioctylphthalate Confined between Surfaces Coated with Long Alkyl Chains

Abstract

To study rheological properties of precipitated calcium carbonate (PCC) dispersion in dioctylphthalate (DOP) in the presence of a small amount of water, ca. 770-2600 ppm, the macroscopic viscosity was measured using a B-type viscometer. The PCC coated with stearic acid dispersed in DOP exhibited higher viscosity than the uncoated PCC. To know the mechanism of this high viscosity, the rheological properties of DOP in nanometer space were investigated using the shear resonance measurement. For this measurement, we used mica surfaces modified with dioctadecyldimethylammoniumbromide (DODA) as a model of PCC surfaces which bears long alkyl chains, and the effects of the surface modification and the addition of water to DOP were examined. For the 1164 ppm water content, we observed that the viscosity of DOP between DODA modified surfaces started to increase at the distance of 57.1 nm, which is much longer than the value for bare mica surfaces, 10.7 nm. When the water content was decreased to 469 ppm, the viscosity started to increase at small distances, 1.1 nm and 8.0 nm for the DODA modified and bare mica surfaces, respectively. These distances were compared with the average particle distance in a DOP sol employed for the macroscopic rheological measurement. Results of the current study indicated that a mechanism of the high viscosity of dispersion of PCC coated with long alkyl chains in DOP would be due to the increasing viscosity of DOP by the combined effects of water and long alkyl chains of the PCC surfaces.