RHEOLOGICAL BEHAVIOR OF A HYDROPHOBICALLY ASSOCIATING WATER-SOLUBLE POLYMER

We have investigated experimentally the behavior of a water soluble as sociating polymer system, hydrophobically modified (hydroxypropyl)guar , with very few randomly distributed hydrophobic substituents along th e chains. We focus mainly on the theological effects due to the superp osition of the reversible hydrophobic interaction network on the physi cal entanglement network in dense macromolecular systems of that kind. Both linear and nonlinear response to transient, steady, and oscillat ory shear flow prove that, in the semidilute and moderately concentrat ed regime, the hydrophobically associating polymer behaves like a clas sical dense macromolecular system whose long-time dynamics can be desc ribed using only one long relaxation time, identified as a retarded di sengagement time, much larger than the association lifetime. The tempo rary hydrophobically associating network can be destroyed when applyin g a critical shear stress tau(c), which is studied as a function of po lymer concentration.