Scaling laws of entangled polysaccharides

Abstract

We study the dilute solution properties and entangled dynamics of hydroxypropyl cellulose (HPC), a semiflexible polymer, in aqueous solution. Intrinsic viscosity data are consistent with a polymer in θ solvent with a Kuhn length ≃22 nm. The overlap concentration, estimated as the reciprocal of the intrinsic viscosity scales with the degree of polymerisation as c* ∝ N^-0.9. We evaluate different methods for estimating the entanglement cross-over, following the de Gennes scaling and hydrodynamic scaling models, and show that these lead to similar results. Above the entanglement concentration, the specific viscosity, longest relaxation time and plateau modulus scale as η_sp ≃ N^3.9c^4.2, τ ≃ N^3.9c^2.4 and G_P ≃ N⁰c^1.9. A comparison with other polymers suggests that the rheological properties displayed by HPC are common to many polysaccharide systems of varying backbone composition, stiffness and solvent quality, as long as the effect of hyper-entanglements can be neglected. On the other hand, the observed scaling laws differ appreciably from those of synthetic flexible polymers in good or θ-solvent.

Keywords: Cellulose; Entanglement; Hydroxypropyl cellulose; Kuhn length; LCST; Polysaccharide; Rheology; Rouse model; Scaling; Viscosity.