Rf. Berg et K. Gruner, REMARKABLY SMALL CRITICAL EXPONENT FOR THE VISCOSITY OF A POLYMER-SOLUTION, The Journal of chemical physics, 101(2), 1994, pp. 1513-1518
We have measured the apparent critical exponent y characterizing the d
ivergence of the viscosity eta(x)(T - T-c)(-Y) near the liquid-liquid
critical point of the mixture polystyrene in diethyl malonate. The dat
a span the range in reduced temperature of 10(-4)<(T - T-c)/T-c<10(-1)
. The sample was prepared from the same materials used by Gruner et al
. in their capillary viscometer [Macromolecules 23, 510 (1990)]; howev
er our torsion oscillator viscometer had a shear rate 80 times lower.
This increased the range of reduced temperatures where shear effects c
ould be neglected. In spite of the large reduction in shear rate and t
he different viscometry technique, the parameters fitted to our data a
nd those of Gruner et al. are in agreement. For this polymer solution,
y is in the range 0.028 +/- 0.003, close to recent results for two ot
her polymer solutions measured in capillary viscometers. However, it i
s significantly smaller than the exponent for pure fluids (0.041 +/- 0
.001) and simple binary mixtures (0.042 +/- 0.002). It appears that po
lymer solutions are in a dynamic universality class different from tha
t of simpler fluids.