NEGATIVE THIXOTROPY OF SOLUTIONS OF PARTIALLY HYDROLYZED POLYACRYLAMIDE .2. THE INFLUENCE OF GLYCEROL CONTENT AND DEGREE OF IONIZATION

We found that the character of negative thixotropy of partially hydrol yzed polyacrylamide in aqueous glycerol strongly depends on polymer co ncentration, glycerol content and shear rate applied. At low polymer a nd glycerol concentrations, shear stress and viscosity slowly increase d during shearing to a limiting value. In addition to this behavior, a steep increase in shear stress as well as normal stress followed by t heir pronounced oscillations occurred at higher concentrations of both components and at higher shear rates. Similarly to the negative thixo tropic effect in solutions of other polymers in organic solvents, the hydrodynamic conditions in which the effects set in seem to be control led by the shear stress acting in the flowing solution; initial kineti cs of the effect depends on solvent viscosity and shear stress applied . To explain the influence of the glycerol content and degree of ioniz ation of the polymer on the minimum shear stress at which the effect s ets in, a decisive role of intermolecular electrostatic repulsions in association of the polymer molecules in shear field is assumed.