A viscoelastic study of dilute aqueous solution of chemically modified cellulose ethers using dynamic light scattering techniques

Abstract

We have established a new system to measure viscoelastic behavior for liquid, which shows too low viscoelasticity to be measured precisely with conventional mechanical rheometers, using modified dynamic light scattering (DLS) techniques. The DLS viscoelastic measurements were carried out for dilute aqueous solutions of chemically modified cellulose ethers (ChMC(1.9-0.25-Mw /103)) with the degree of substitution by methoxy groups of 1.9, that by hydroxypropoxy groups of 0.25 and the nominal weight average molecular weight of Mw = 75000, 300000 and 380000 containing a small amount of poly(styrene) latex (PL) beads with the radius of 0.05 μm. The dependence of creep compliance (J(t )) on time (t ) was evaluated from the auto-correlation function of fluctuating scattered light intensity because of Brownian motions of dispersed PL beads. The viscoelasticity obtained from J(t ) data revealed that ChMC(1.9-0.25-Mw /103)s do not behave as flexible polymer chains, but rigid rod-like molecules with the length of 130, 320 and 360 nm, respectively.