The influence of shear rate, temperature and chain conformation on the critical concentration c

When viscometry is used, a crossover phenomenon is observed separating the dilute solutions into extremely dilute solutions and dilute solutions. The critical concentration c**, determined from this crossover phenomenon, strongly depends on the shear rate in the solution. At very high values of shear rate the critical concentration c** becomes very low and depends only on the contour length of the elongated chains of different polymers. An increase of the temperature induces an increase of c** because the relaxation time of the chains decreases. If a polymer adopts a rodlike conformation (in a given solvent at a given temperature) the excluded volume of its chains increases and its critical concentration c** decreases.