Thixotropy of aqueous solution of fluorocarbon-modified poly(acrylic acid)
AbstractThe rheological properties of the aqueous solution of 1H,1H,11Hperfluoroundecyl acrylate -modified poly(acrylic acid) were studied. It was found that the solutions show different viscosity dependence on shear time at different pH and shear rates. At lower pH and moderate shear rates, the viscosity of the solutions shows a great increase with time. At pH 5.0 and above, it exhibits thixotropy at any shear rate, i.e., the viscosity decreases with time at constant shear rates. If the shearing stops, the viscosity of the solutions can be recovered to some extent. These phenomena are interpreted to be due to the intermolecular hydrophobic association: the construction of the association leads to an increase of the viscosity, the destroying of the association leads to a decrease of the viscosity. The pH-induced conformational change and the shearing-induced chain elongation jointly influence the intermolecular hydrophobic association.