0000000000160848
AUTHOR
M. Ballauff
Rheological studies of moderately concentrated polystyrene solutions. I. A new method for the extrapolation of the zero-shear viscosity
Measurements of the viscosity coefficient η of solutions of polystyrene (Mw = 6.0 × 105 and 1.77 × 106) in trans-decalin (TD, θ solvent) and toluene (TL, good solvent) as function of shear rate (11−104 s−1), concentration (4.24−11.21 wt %), and temperature (10–50°C) are reported. As a new theoretically grounded method for the determination of the zero-shear viscosity η0 it is proposed to plot η as a function of . The intercepts of the straight lines obtained by this procedure give η0 in good agreement with directly measured values.
Sedimentation of dissolved macromolecules in the vicinity of the consolute point 1. Strictly binary systems and kinetic considerations
This paper analyzes the effect of gravity on polymer solutions near the consolute point. Calculations are carried out for monodisperse polystyrene in cyclohexane using the Flory-Huggins expression with a concentration-dependent interaction parameter for the free energy of mixing. Depending on molecular weight and distance to the demixing temperature, the influence of gravity leads to non-negligible gradients of the volume fraction in the one-phase region as well as in the two-phase region. In particular, the effect of gravity on the measurement of the coexistence curve in a finite sample is calculated explicitly.
Thermodynamically induced shear degradation
The shear degradation of polymers in semiconcentrated solutions is viewed as a function of solvent quality. It is shown that the deterioration of the thermodynamic quality of the solvent leads to a marked flow resistance due to an increasing number of contacts between the chains. This may be probed by viscosimetric measurements as well as by degradation experiments (“thermodynamically induced shear degradation”). For a detailed discussion of this phenomenon the experimental setup for the mechanochemical experiment is outlined first, followed by a survey of the kinetics of chain scission. Finally, experiments mostly obtained on polystyrene in the theta-solvent trans-decalin are discussed. Th…
Rheological studies of moderately concentrated polystyrene solutions in the vicinity of the θ temperature. II. Shear-rate dependence for different thermodynamic conditions
The viscosity data of moderately concentrated polystyrene solutions in trans-decalin (TD) (θ solvent, θ temperature 21°C) and toluene (TL) (good solvent) reported in Part I are discussed in terms of Graessley's entanglement theory. Under good solvent conditions, Graessley's master curve provides an excellent fit up to high shear rates, whereas in the vicinity of the θ conditions the data have to be modified by a parameter ηfric introduced by Ito and Shishido. The characteristic time of mechanical response to flow of chains approximately given by the shift factor τ0 is found in good solvents to be on the order of the Rouse relaxation time. In poor solvents, close to demixing, τ0 tends to muc…