Rheology Of Transient Networks Formed By The Association Of Hydrophobically Modified Water Soluble Polymers

Abstract

This chapter discusses the rheological properties of associating polymers in solution and as mixtures with polymer lattices and surfactants. There are different types of associating polymers, but the emphasis is on the telechelic hydrophobically modified ethoxylated urethanes (HEUR) polymers. The chapter describes how the polymer architecture and molecular weight may affect the rheology. For the telechelic systems, simple Maxwellian viscoelastic response is observed, consistent with a picture in which stress relaxation occurs through end-group disengagement, followed by a much faster Rouse relaxation of the polymer chain. Such a mechanism is also consistent with the observation that the viscoelastic spectrums of HEUR-AT (associative thickeners) with different hydrophobe lengths possess the same number of relaxation times as there are components in the blend. As a consequence, it is possible, through control of the blend ratios of the components, to produce fluids with designed relaxation spectra. A simple model, in which looped and bridged chains coexist within an infinite network, can describe many of the rheological properties of telechelic ATs. Such a picture can be readily used to describe various rheological features, including the concentration dependencies of the viscoelastic modulus, relaxation time, and viscosity, the correct scaling for the molecular weight dependence of the relaxation time, and the effect of surfactants on the elastic modulus.