Comprehensive physical visualisation of the chain conformation and solution property of carboxymethylated konjac glucomannan: Comparison of charged and uncharged polyelectrolytes

Abstract

The present work deals with a comprehensive molecular characterization and delineation of solution property of a series of charged and uncharged carboxymethylated konjac glucomannan (CMKGM) with different molecular weights (Mw, 1.57 × 105–7.33 × 105) and degrees of substitution (DS, 0.19–1.63) by using various rheological models and solution scaling theory. CMKGM macromolecules in aqueous solutions are found to adopt semi-flexible chain conformation and show a tendency close to rigid chains with decreasing Mw and increasing DS. For uncharged CMKGM solutions, the Huggins–Kraemer, Heller, Fuoss and Wolf approaches can achieve equally excellent fitting results for the determination of intrinsic viscosity [η], whereas for charged CMKGM solutions, only the Huggins–Kraemer and Wolf plots are valid. In accordance with the physical scaling law, a scaling relationship exists between rheological parameters and concentration c for salt and salt-free aqueous solutions of CMKGM. The relationship of specific viscosity ηsp ~ c[η] and ηsp ~ c ~ Mw is derived for CMKGM in a high ionic strength environment (NaCl 0.15 M) by using the Kulicke-Keniewske approach. The constitutive models of the linear Maxwell model and two kinds of non-linear PTT and Giesekus models have also been applied to quantitatively describe the rheological properties of CMKGM entangled solutions under either dynamic or steady shear flow.