Related Experiment Video
Updated: Jun 20, 2026
09:34
Extraction and Characterization of Surfactants from Atmospheric Aerosols
Published on: April 21, 2017
Activity of surface active substances determined from their surface excess.
Gunther Andersson1, Thomas Krebs, Harald Morgner
1Wilhelm-Ostwald Institute for Physical and Theoretical Chemistry, Leipzig University, Leipzig, Germany. g.andersson@rz.uni-leipzig.de
Physical Chemistry Chemical Physics : PCCP
|September 30, 2009
Summary
This study directly measures surface excess using neutral impact collision ion scattering spectroscopy (NICISS) to determine surfactant activity coefficients, overcoming limitations of traditional methods for tetrabutylphosphonium bromide in formamide.
Area of Science:
- Physical Chemistry
- Surface Science
- Materials Science
Background:
- The Gibbs equation traditionally relates surface tension, surface excess, and activity.
- Determining surfactant activity coefficients is challenging due to low bulk concentrations.
- Direct measurement of surface excess offers an alternative approach.
Purpose of the Study:
- To directly measure surface excess for surfactant solutions.
- To determine activity coefficients using directly measured surface excess and known surface tension.
- To investigate the system of tetrabutylphosphonium bromide in formamide.
Main Methods:
- Utilizing neutral impact collision ion scattering spectroscopy (NICISS) for direct surface excess determination.
- Measuring concentration depth profiles with angstrom-level resolution.
- Applying the Gibbs equation with directly obtained surface excess data.
Main Results:
- Successfully measured surface excess for tetrabutylphosphonium bromide (Bu4PBr) in formamide.
- Demonstrated the feasibility of determining activity coefficients via direct surface excess measurement.
- Provided insights into the surface behavior of Bu4PBr in a polar solvent.
Conclusions:
- Direct surface excess measurement using NICISS is a viable method for calculating surfactant activity coefficients.
- This approach overcomes limitations associated with indirect methods relying on bulk property changes.
- The study validates a novel pathway for characterizing surfactant solutions.
Related Concept Videos
01:27Surface Active Agents
Surfactants, named for their behavior at interfaces, positively adsorb at the interfaces of two phases, reducing interfacial tension. Their versatility as emulsifiers, detergents, and foaming agents stems from this ability. Surfactants, often termed amphiphiles, share the property of amphipathy, with molecules having both hydrophilic and hydrophobic portions. The hydrophilic part is called the head, and the hydrophobic part, including an elongated alkyl substituent, forms the tail.Surfactants...
01:16Surface Tension and Surface Energy
When a paint brush is immersed in water, the bristles wave freely inside the water. When it is taken out, the bristles stick together. The reason behind this effect is surface tension.
Consider a beaker filled with liquid. The bulk molecules in the liquid experience equal attractive forces on all sides with the surrounding molecules. However, the surface molecules experience a net attractive force downward due to the bulk molecules. The surface of the liquid behaves like a stretched membrane,...
Consider a beaker filled with liquid. The bulk molecules in the liquid experience equal attractive forces on all sides with the surrounding molecules. However, the surface molecules experience a net attractive force downward due to the bulk molecules. The surface of the liquid behaves like a stretched membrane,...
01:24Thermodynamics: Activity Coefficient
Activity is the measure of the effective concentration of the species in solution. It can be expressed as the product of the molar concentration of the species and its activity coefficient. The activity coefficient is a dimensionless quantity and depends on the total ionic strength of the solution.
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
01:24Surface Tension
Surface tension is defined as the force per unit length (γ) acting along the surface of a liquid. It arises due to strong intermolecular forces of attraction. A molecule located inside the bulk of the liquid is surrounded by other molecules and experiences equal forces in all directions. However, a molecule at the surface experiences unbalanced forces because there are more neighboring molecules below than above. This creates a net inward force that pulls surface molecules toward the interior,...
01:10Thermodynamics: Chemical Potential and Activity
The effective concentration of a species in a solution can be expressed precisely in terms of its activity. Activity considers the effect of electrolytes present in the vicinity of the species of interest and depends on the ionic strength of the solution. The activity of a species is expressed as the product of molar concentration and the activity coefficient of the species.
The thermodynamic equilibrium constant is more accurately defined in terms of activity rather than concentration.
The thermodynamic equilibrium constant is more accurately defined in terms of activity rather than concentration.
02:57Surface Tension, Capillary Action, and Viscosity
Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...