Abstract
In this paper, the linear and nonlinear rheological behavior of semidilute aqueous solutions of a recently synthesized thermoassociative graft copolymer was investigated, as a function of temperature and polymer concentration. The polymer, namely CMC–g–PNIPAM, is based on a carboxymethylcellulose (CMC) backbone bearing thermosensitive poly(N-isopropylacrylamide) (PNIPAM) sidechains. The samples have been submitted to steady shear, oscillatory shear, and step-strain experiments, mainly at temperatures above the threshold temperature Tassoc to observe thermothickening. The linear and nonlinear rheological data clearly show the existence of two temperature regimes, separated by a transition temperature T′ > Tassoc. At temperatures below T′, the solutions behave like a soft critical gel, corresponding to weak PNIPAM segregation. At temperatures above T′, the solutions behave like a stiff critical gel, corresponding to strong PNIPAM segregation.
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