Effective Viscosity of Polymer Solutions: Relation to the Determination of the Depletion Thickness and Thickness of the Adsorbed Layer of Cellulose Derivatives

✍ Scribed by C.W. Hoogendam; J.C.W. Peters; R. Tuinier; A. de Keizer; M.A. Cohen Stuart; B.H. Bijsterbosch

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 159 KB
• Volume: 207
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5762

✦ Synopsis

The diffusion of silica particles with radii ranging from 12 to 510 nm in dilute solutions of carboxymethyl cellulose (M w ‫؍‬ 180 to 1200 kg mol ؊1 , c CMC ‫؍‬ 5 to 1000 mg l ؊1 ) was investigated by means of dynamic light scattering at pH 5 in 0.01 mol l ؊1 NaCl. The viscosity of the polymer solution as experienced by the silica probes (the "microscopic" or effective viscosity, eff ) differs from the viscosity as determined by capillary viscometry ( p ). For small particles eff nearly equals the viscosity of the solvent ( 0 ). The effective viscosity increases with the size of the probe particles and the polymer concentration but remains less than p . The effective viscosity is interpreted in terms of a model in which the particle is surrounded by a layer of polymer free solution ( ‫؍‬ 0 ). The thickness of the polymer-free layer is assumed to be equal to the thickness of the depletion layer ( d ). Applying this model, a decrease in d as a function of CMC concentration is observed. At low concentration d equals the radius of gyration. The hydrodynamic layer thickness (␦ h ) of cellulose derivatives (carboxymethyl cellulose and hydroxyethyl cellulose) adsorbed on inorganic oxide surfaces (␣-Fe 2 O 3 and SiO 2 ) is also investigated by dynamic light scattering. Upon using p maxima in ␦ h are found. However, these maxima are a consequence of an incorrect choice of the viscosity. When the viscosity is used as obtained from inert probe diffusion, no anomalies are observed.