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

The relationship between shear and extensional viscosities of a series of m odel hydrophobically modified alkali-soluble associative (HASE) polymers wi th varying degree of hydrophobicity was investigated. An opposing jet rheom eter (Rheometric RFX) was used to measure the extensional and shear viscosi ties 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 exponential ly with the hydrophobicity and concentration of the polymers. This is attri buted to the increase in the strength of the associative junctions. Extensi onal thickening is observed at moderate extensional rates for the polymer w ith C12H25 hydrophobes. This indicates that associative polymer with shorte r hydrophobic chain undergoes a conversion from aggregated clusters with pr edominantly intra-molecular associations at low extension rates to inter-mo lecular cluster associations at moderate deformation rates. At high extensi onal rates, the deformation force exceeds the strength of inter-cluster ass ociations, resulting in the destruction of the active junctions, yielding a continuous decrease in the extensional viscosity. The Trouton ratio increa ses with deformation rates, polymer concentration and the size of the hydro phobes. (C) 2000 Elsevier Science B.V. All rights reserved.