Hydrodynamic and Colloidal Interactions in Concentrated Charge-Stabilized Polymer Dispersions

Area of Science:

• Colloid and Surface Science
• Rheology
• Materials Science

Background:

• Colloidal dispersions are ubiquitous in nature and industry.
• Understanding their behavior requires characterizing hydrodynamic and colloidal interactions.
• Charge-stabilized dispersions are particularly sensitive to environmental factors like salt concentration.

Purpose of the Study:

• To investigate hydrodynamic and colloidal interactions in concentrated, charge-stabilized colloidal dispersions.
• To determine the dependence of rheological properties and self-diffusivity on salt content, particle size, and concentration.
• To compare different methods for measuring colloidal surface charge and their reliability.

Main Methods:

• Synthesized sulfonated polystyrene lattices of varying diameters.
• Employed shear rheology, high-frequency torsional resonance, electrophoresis, titration, and dynamic light scattering.
• Measured low and high-shear viscosity, high-frequency viscosity, modulus, and self-diffusivity.

Main Results:

• High-frequency and high-shear viscosity are dominated by hydrodynamic interactions but differ due to microstructure distortion.
• Short-time self-diffusion is insensitive to direct particle interactions and shows a different concentration dependence than high-frequency viscosity.
• High-frequency elastic modulus measurements yield apparent surface charge in agreement with coagulation and theory, but not electrophoresis.

Conclusions:

• High-frequency rheology provides a more reliable measure of effective surface charge and salt stability than electrophoretic mobility (zeta-potential).
• Rotational rheometry underestimates the high-frequency modulus and surface charge in concentrated dispersions.
• A generalized Stokes-Einstein relationship is violated for the studied properties.