Profile Analysis Tensiometers
Advanced instruments for surface and interfacial characterization.
Surface & Interfacial Tension · Chapter 04
Adsorption &Surface Chemistry
Adsorption at liquid interfaces, concentration-dependent interfacial tension and models describing interfacial coverage and molecular organization.
Chapter contents
07
Scientific topics
Chapter Overview
From interfacial adsorption to molecular organization.
Surface-active solutes change interfacial tension because the equilibrium composition of the interface differs from that of the bulk. Gibbs adsorption thermodynamics relates changes in interfacial tension to surface excess and changes in the chemical potentials of the components.
Adsorption models provide different physical descriptions of the interfacial layer. The Henry model describes the dilute limit, Langmuir adsorption introduces finite interfacial capacity, and the Frumkin framework accounts for interactions between adsorbed molecules. More advanced descriptions consider molecular reorientation and two-dimensional aggregation.
Adsorption Library
Explore adsorption at liquid interfaces.
Scientific topics covering concentration-dependent adsorption, classical adsorption models and changes in the organization of interfacial layers.
01
Interfacial adsorption
Adsorption at Liquid Interfaces
Surface-active solutes change interfacial tension because the equilibrium composition of the interface differs from that of the adjoining bulk phase.
Surface-active solutesInterfacial compositionSurface tension
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02
Concentration dependence
Adsorption, Micellization & the CMC
As surfactant concentration increases, interfacial coverage typically increases and surface tension decreases. At sufficiently high concentration, micelles or other aggregates can form.
MicellizationCritical micelle concentrationγ vs. log c
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03
Dilute limit
Henry Adsorption
The Henry model describes the low-coverage limit in which adsorbed amount is proportional to bulk concentration and significant excluded-area or lateral interactions are absent.
Henry modelLow coverageΓ = Kc
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04
Finite interfacial capacity
Langmuir Adsorption
The Langmuir model introduces finite interfacial capacity and describes increasing fractional coverage as concentration rises while neglecting lateral molecular interactions beyond occupancy restrictions.
Langmuir isothermFinite capacitySurface coverage
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05
Lateral interactions
Frumkin Adsorption
The Frumkin framework extends Langmuir adsorption by accounting for interactions between adsorbed molecules, which modify the relation between bulk activity and interfacial coverage.
Frumkin isothermLateral interactionsInterfacial coverage
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06
Surface-tension relation
Szyszkowski Equation
The Szyszkowski relation provides a classical description of the concentration dependence of surface tension and is closely connected to Langmuir-type adsorption under appropriate assumptions.
Szyszkowski equationγ(c)Langmuir adsorption
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07
Interfacial organization
Reorientation & Interfacial Aggregation
Adsorbed molecules can change orientation as surface coverage increases, while lateral association at higher coverage can lead to two-dimensional aggregates within the adsorption layer.
ReorientationMolecular area2D aggregation
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Adsorption Models
Different models represent different interfacial states.
Adsorption models are not interchangeable fitting functions. Each represents a particular physical description of the interfacial layer.