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Effect of surfactant interfacial orientation/aggregation on adsorption dynamics.
V B Fainerman1, R Miller, E V Aksenenko
1International Medical Physicochemical Centre, Donetsk Medical University, Ukraine.
Advances in Colloid and Interface Science
|May 8, 2000
Summary
New thermodynamic models improve surfactant adsorption descriptions by accounting for interfacial reorientation and aggregation. These models provide accurate diffusion coefficients for various surfactants, including alkyl dimethyl phosphine oxides and oxyethylated non-ionics.
Area of Science:
- Physical Chemistry
- Surface Science
- Colloid Science
Background:
- Surfactant adsorption kinetics are crucial for understanding interfacial phenomena.
- Classical diffusion models often fail to accurately describe surfactant adsorption, especially for higher homologues.
- Interfacial reorientation and aggregation play significant roles in surfactant behavior.
Purpose of the Study:
- To develop and apply new thermodynamic adsorption isotherms to improve the description of surfactant adsorption kinetics.
- To investigate the influence of interfacial reorientation and aggregation on diffusion coefficients.
- To provide a more accurate theoretical framework for surfactant adsorption modeling.
Main Methods:
- Application of novel thermodynamic adsorption isotherms.
- Analysis of diffusional transport mechanisms in surfactant adsorption.
- Modeling interfacial reorientation and aggregation effects.
- Fitting experimental data for alkyl dimethyl phosphine oxides, oxyethylated non-ionics, and 1-decanol solutions.
Main Results:
- Consideration of interfacial reorientation corrects diffusion coefficients that appear too high.
- Accounting for interfacial aggregation prevents diffusion coefficients from being too small or requiring adsorption barriers.
- The model accurately describes adsorption kinetics for alkyl dimethyl phosphine oxides (C8-C15) and oxyethylated non-ionics (C10EO8).
- A mean surface aggregation number (n=2.5) was determined for 1-decanol, consistent with equilibrium adsorption data.
- Incorporating rate constants for transitions between adsorption states significantly improves kinetic curve fitting.
Conclusions:
- New thermodynamic models offer a superior description of surfactant adsorption kinetics compared to classical diffusion models.
- Interfacial reorientation and aggregation are essential factors for accurate kinetic modeling.
- The developed models are applicable to a range of surfactants, enhancing predictive capabilities in surface science.