Colloidal Charge Determination in Concentrated Liquid Dispersions Using Torsional Resonance Oscillation

✍ Scribed by J. Bergenholtz; N. Willenbacher; N.J. Wagner; B. Morrison; D. van den Ende; J. Mellema

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 239 KB
• Volume: 202
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5463

✦ Synopsis

cles, e.g., conductivity (7) or electroacoustic spectroscopy The high-frequency rheology of concentrated liquid charge-sta- (8). Hence, these methods require operations at low particle bilized dispersions has been measured using a surface-loaded torconcentrations at which the simplified theoretical considerasional resonator. The high-frequency shear moduli are extracted tions allow for conversion of the measurement to surface from the measurement as a function of ionic strength and surface charge or potential. Another simplification sometimes made acid content. A theory which enables the determination of the is using the linearized version of the Poisson-Boltzmann effective surface charge of the concentrated dispersions is preequation in the analysis of various measurements, such as sented. At high ionic strengths the theory simplifies to an analytic small-angle scattering (9, 10), conductivity (11), and selfformula relating the effective surface charge to the high-frequency diffusion (12). The proviso for using the simpler linear thelimiting shear modulus in terms of an effective hard-sphere diameter. The effective hard-sphere diameter is obtained experimentally ory is that the bare surface charge must be renormalized, from the high concentration asymptote of the zero-shear viscosity. that is, replaced by an effective charge, smaller than the The resulting effective surface charge increases with added electrobare charge (13-15). Consequently, discrepancies are found lyte content in agreement with charge renormalization theory. The between the charge determined by conductometric titration, effective charge also increases with added weak and strong surface which yields the total surface charge, and the effective acid content. The method, which operates on concentrated dispercharge resulting from analyses using the linear Poissonsions, is found to yield effective charges that agree with dilute Boltzmann theory (16). In addition, one expects that the measurements of the electrophoretic mobility. Moreover, the effeceffective charge will show some dependence on the type of tive hard-sphere scaling reduces the high-frequency viscosity to a measurement used as well as on dispersion properties.