Methods for determining the intrinsic and effective charges on spherical macroions
J M Roberts1, J J O'De, J G Osteryoung
1Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204.
Analytical Chemistry
|June 8, 2011
Summary
This study quantifies particle charge in latex suspensions using voltammetry. It reveals that the effective charge (Z*) is less than the intrinsic charge (Z) due to counterion binding, impacting macroion behavior.
Area of Science:
- Colloid and Surface Science
- Electrochemistry
- Physical Chemistry
Background:
- Understanding the charge on colloidal particles is crucial for predicting their behavior in suspensions.
- Previous methods for determining particle charge include titration and electrophoresis, yielding intrinsic (Z) and effective (Z*) charges, respectively.
Purpose of the Study:
- To accurately measure the intrinsic and effective charges of sulfonated polystyrene latex particles.
- To investigate the relationship between intrinsic charge, effective charge, and particle properties.
Main Methods:
- Utilized steady-state voltammetric transport-limited currents for hydrogen counterion reduction at a platinum disk microelectrode.
- Employed deionized latex suspensions with excess supporting electrolyte.
- Compared voltammetric results with titration and electrophoresis data.
Main Results:
- Voltammetry accurately determined intrinsic charge (Z) and effective charge (Z*).
- Found that effective charge (Z*) is consistently lower than intrinsic charge (Z) due to electrostatic binding of counterions.
- Observed that the ratio Z*/Z decreases with increasing Z/a (intrinsic charge to particle radius ratio).
Conclusions:
- Voltammetric measurements provide a reliable method for determining both intrinsic and effective charges of colloidal particles.
- The discrepancy between Z and Z* is explained by counterion condensation, influencing macroion behavior.
- The findings align with theoretical models like the cell model using the nonlinear Poisson-Boltzmann equation.
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