Determination of the Flory Exponent by Study of Steady Shear Viscosity

Abstract

The aim of the present work was to determine first the behavior of a neutral polymer, polyvinylpyrrolidone (Mw = 3,6 105 g/mol), in the dilute and semidilute regimes in water by a rotational concentric cylinder viscometer and then to deduce the Flory exponent. The absolute viscosity of the samples was directly determined from the shear stress–shear rate rheograms over a temperature range of 20°C–40°C and a polymer concentration range of 0.114–1.438 g/dl. The rheological nature of the polymer solutions was systematically analyzed, showing Newtonian behavior. Then, the intrinsic viscosity [η] was determined according to the Schultz–Blaschke equation. The overlapping concentration C* was determined by plotting the double logarithmic plots of reduced viscosity ηr versus polymer concentration C, yielding . The Flory exponents, ν, were deduced from viscosity measurements in the semidilute regime (ν = 0.544). In addition, the hydrodynamic radius, RH, was measured for different polymer molar mass (Mw (g/mol) = 10,000, 40,000, 50,000, and 360,000) by a dynamic light scattering technique at 25°C, yielding a Flory exponent at this temperature of 0.521. The obtained value was thus in agreement with that obtained by the rheological method in the semidilute regime with a relative deviation close to 4.5%.