The Viscosity of Solutions of Poly(propylene imine) Dendrimers in Methanol.
The viscosity of solutions of poly(propylene imine) dendrimers in methanol has been determined. An Ubbelohde and a low-shear rotational viscometer have been used. The viscosity was Newtonian for every concentration and shear rate used. The value of the Huggins coefficient indicates soft sphere behavior. The viscosity of the lower generations as a function of the volume fraction can be described with a single exponent, where the exponent is comparable to the intrinsic viscosity. The viscosity of the 4th and 5th generation dendrimers shows a stronger increase from a volume fraction of about 0.15 to 0.30. This increase is much smaller than that expected, using the Krieger-Dougherty formula for hard spheres with the hydrodynamic radius determined from the intrinsic viscosity. This smaller increase and the small value of the Huggins coefficient are interpreted in terms of a breakdown of the solvation layer. At a volume fraction of 0.3 the dendrimers, using the radius of gyration as the radius, start to touch each other. From the dependence of the viscosity on the concentration and the dependence of the viscosity on the molar weight, it can be concluded that dendrimers do not interpenetrate. It is concluded that they deform (collapse). Copyright 2001 Academic Press.
Colloid and Interface Science Group, Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Leiden, 2300 RA, The Netherlands
Ivo B.
IB
Rietveld
Dick
D
Bedeaux