Rod particle-like viscoelastic behavior of hydroxypropylmethyl cellulose samples with narrow molar mass distributions...

The viscoelastic behaviors of aqueous solutions of hydroxypropylmethyl cellulose (HpMC) samples with narrow molar mass distributions were investigated over a wide concentration (c) range. The degree of substitution by methyl groups and the molar substitution number by hydroxypropyl groups of the samples were 1.8 and 0.15. The weight average molar masses (M_w) were 210, 310 and 440 kg mol^-1, and the molar mass distribution indices were less than 1.3 for each sample. The zero-shear viscosity (η₀), the average relaxation time (τ_w), and the steady state compliance (J_e) determined in the c range for HpMC molecules to fully entangle were determined using the molecular number density (ν = cN_A/M_w, where N_A is the Avogadro constant) and the rod particle length (L) of HpMC molecules. The results were reasonably understood on the basis of entangled rod particle suspension rheology, in which η₀ and τ_w are described with L³ν and J_e^-1 is described with ν. Consequently, all the obtained viscoelastic data clearly revealed that the HpMC molecules behave as rod-like particles even in a fully entangled concentration range.