i.e., independent of shear rate, and high. At very high shear rate, the time
allowed for entanglements to form is very short, and the molecules are
(almost) fully disentangled, yielding a relatively low viscosity. The relation
between apparent viscosityZ*and shear rate depends on polymer type and
concentration and on solvent quality.
Question 1
Consider an aqueous solution of carrageenan, at a concentration above the chain
overlap concentration, and compare it with a solution of the same mass
concentration, but with a carrageenan of larger molar mass. Would the following
properties be larger, smaller or the same?
Apparent viscosity
Dependence of apparent viscosity on concentration
Extent of shear rate thinning
Correlation length
What would happen if to the carrageenan solution an equal volume were added of
Water
Ethanol
NaCl solution, final concentration 0.1 molar
HCl solution, final concentration 1 molar
FIGURE6.16 Entanglements. Depicted are two polymer chains. At (a) they form
an entanglement, but not at (b) or (c).