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  • The first normal stress difference and viscosity in shear of liquid crystalline solutions of hydroxypropylcellulose: new experimental data and theory
    Publication . Fried, F.; Leal, Catarina R.; Godinho, M. H.; Martins, A. F.
    The constitutive equations for liquid crystalline polymers recently proposed by one of us [1] are applied here to interpret the behaviour of the shear viscosity η equation image and the first normal stress difference N1($ \dot \gamma $equation image) measured for liquid crystalline (LC) solutions of hydroxypropylcellulose in acetic acid. N1(equation image) is observed to change from positive to negative and again to positive, as the shear rate $ \dot \gamma $equation image increases, at lower concentrations, in the LC phase. The $ \dot \gamma $equation image-values at which N1 changes sign depend on the molecular mass (degree of polymerization) and on the concentration. η $ \dot \gamma $equation image shows a small Newtonian plateau at low shear rates and a strong shear-thinning at higher values of $ \dot \gamma $equation image. The rate of decrease of η $ \dot \gamma $equation image in this region shows an “hesitation” similar to one previously observed in LC solutions of poly-γ-benzyl-L-glutamate PBLG. All these observations can be rationalized within the frame-work of Martins' theory. The expressions for N1($ \dot \gamma $equation image) and η $ \dot \gamma $equation image derived from this theory fit very well (quantitatively) to the experimental data and some fundamental viscoelastic parameters of the system under study are thereby obtained for the first time.
    1994-09Journal article Restricted access Show more