Shear-thinning of ‘random coil’ polysaccharides: Characterisation by two parameters from a simple linear plot

Abstract

The shear-thinning behaviour of solutions of conformationally disordered (‘random coil’) polysaccharides, at concentrations above the onset of coil-overlap and entanglement (i.e. above c∗), can be matched, with reasonable precision, by the equation: η=η= 0⧸[1 + ( λ λ 1 2 ) 0.76] Thus viscosity (η) at any shear rate (γ) can be characterised by two parameters: the maximum ‘zero-shear’ viscosity ( η 0) and the shear rate ( γ ̇ 1 2 ) at which viscosity is reduced to η 0 2 . The values of η 0 and γ ̇ 1 2 can be derived from, respectively, the intercept and slope of a simple linear plot of η versus η γ ̇ 0·76 . The method can also be applied to other ‘random coil’ polymers of reasonably high polydispersity, and to the analysis of the frequency (ω) dependence of dynamic viscosity (η∗) from small-deformation oscillatory measurements.