Dynamic rheological measurements on hydroxypropylcellulose solutions

Abstract

Loss and storage moduli were measured by eccentric disk rheometry for isotropic and anisotropic hydroxypropylcellulose solutions. Two rheological regimes exist for the anisotropic solution, one at low deformation ratios (less than 80%) and one at high deformation ratios (more than 100%). For the high‐deformation regime, the comparison between dynamic and steady‐state parameters is consistent with what is known from the literature. The data on the low‐deformation regime are new and are characterized by loss and storage moduli two orders of magnitude larger than those in the high‐deformation regime. This difference is not due to a cholesteric to nematic transition nor to an elastic to viscoelastic transition (yield stress). It is postulated that a network of defects stabilized by chain molecules could give such a low deformation behavior.

Shear flow of liquid-crystalline polymer solutions as investigated by small-angle light-scattering techniques

“…In this shear rate range the rheooptical behavior is characterized by Vv and VH (or Hv) patterns similar in shape and having nearly equal intensities, which means that the orientation correlations are governing the flow; i.e., density and concentration fluctuations are insignificant,26 The role of the disclinations in the rheology has been emphasized by two of the authors. 30 To explain the unusual rheological behavior of cholesteric HPC-water solution, they suggest that defects (disclinations) form a network (e) ^r3s' (f)…”