Extensional properties of model hydrophobically modified alkali-soluble associative (HASE) polymer solutions

The relationship between shear and extensional viscosities of a series of model hydrophobically modified alkali-soluble associative (HASE) polymers with varying degree of hydrophobicity was investigated. An opposing jet rheometer (Rheometric RFX) was used to measure the extensional and shear viscosities of 0.3-4.0 wt.% solutions. The deformation rates were varied from 0.1 to 10,000 s(-1). The shear and extensional viscosities increase exponentially with the hydrophobicity and concentration of the polymers. This is attributed to the increase in the strength of the associative junctions. Extensional thickening is observed at moderate extensional rates for the polymer with C12H25 hydrophobes. This indicates that associative polymer with shorter hydrophobic chain undergoes a conversion from aggregated clusters with predominantly intra-molecular associations at low extension rates to inter-molecular cluster associations at moderate deformation rates. At high extensional rates, the deformation force exceeds the strength of inter-cluster associations, resulting in the destruction of the active junctions, yielding a continuous decrease in the extensional viscosity. The Trouton ratio increases with deformation rates, polymer concentration and the size of the hydrophobes. (C) 2000 Elsevier Science B.V. All rights reserved.