On the Number of Blobs per Entanglement in Semidilute and Good Solvent Solution: Melt Influence

Measurements of viscoelastic properties in good solvent semidilute solution are reported for three linear polymer species: polystyrene, polyisoprene, and polybutadiene. It is shown that using the same reduced concentration C/C^∗ as for static properties, three different curvss are obtained for the reduced viscosity η/η_solvent. The scaling used for static properties is no longer valid and a number n_e of blobs per chains are needed for polymers to be entangled. This number, here determined by the ratio of the osmotic modulus to the elastic modulus K/G = n_e, is found to be different for the three kinds of polymer and identical to the number of monomers per entanglement measured in the melt. The reduced variables for the viscosity are η/η_Rouse as a function of C/C_e where η_Rouse = η_solvent(C/C^∗)^1.30 is the viscosity predicted by the Rouse model and C_e = n_e^0.76C^∗ is the concentration at which polymers begin to be entangled.