Surface and Colloid Chemistry
Surface and colloid chemistry studies the physics and chemistry of interfaces and finely divided matter, where the large surface area to volume ratio makes interfacial forces dominate behaviour.
Definition
Surface and colloid chemistry is the branch of physical chemistry concerned with the properties of interfaces and of colloidal systems, in which one substance is finely dispersed in another and interfacial phenomena govern behaviour.
Scope
This area covers the chemistry of interfaces and dispersed systems: surface tension and the thermodynamics of interfaces; adsorption of gases and solutes onto surfaces and its isotherms; the properties and stability of colloidal dispersions; surfactants and their self-assembly into micelles and membranes; and the structure of charged interfaces and the electrical double layer. The catalytic chemistry of surfaces is connected to kinetics, while here the emphasis is on interfacial thermodynamics, forces, and structure.
Sub-topics
Core questions
- How does surface tension arise from the thermodynamics of interfaces?
- How do molecules adsorb onto surfaces, and what isotherms describe the process?
- What forces stabilize or destabilize colloidal dispersions?
- How do surfactants self-assemble, and how do charged interfaces structure the surrounding solution?
Key concepts
- Surface tension and interfacial energy
- Adsorption isotherms
- Colloidal dispersions and stability
- Surfactants and self-assembly
- Electrical double layer
Key theories
- Langmuir adsorption isotherm
- Adsorption onto a uniform surface with a fixed number of equivalent sites and no interaction between adsorbed molecules leads to a coverage that saturates with pressure or concentration, the foundational model of surface adsorption.
- DLVO theory of colloid stability
- The stability of charged colloids is governed by the balance between attractive van der Waals forces and repulsive electrical double-layer forces, explaining why dispersions flocculate when added salt screens the repulsion.
Clinical relevance
Surface and colloid chemistry underlies heterogeneous catalysis, detergents and emulsions, paints, foods, and pharmaceuticals, the stability of inks and ceramics, the behaviour of biological membranes and cells, and processes such as flotation, wetting, and water treatment.
History
Thomas Graham distinguished colloids from crystalloids in the 1860s; Gibbs gave interfaces a thermodynamic foundation, Langmuir's early twentieth-century work established the molecular theory of adsorption and monolayers, and the DLVO theory of the 1940s explained colloidal stability quantitatively.
Key figures
- Irving Langmuir
- Thomas Graham
- Jacob Israelachvili
Related topics
Seminal works
- langmuir1916
- adamson1997
- israelachvili2011
Frequently asked questions
- Why do interfacial effects dominate in colloids but not in bulk matter?
- Colloidal particles are so small that an enormous fraction of their molecules sit at the surface; the resulting huge surface area to volume ratio makes interfacial energy and forces, negligible in bulk samples, control the system's behaviour.
- What keeps a colloidal dispersion from settling out?
- Repulsive forces between particles, chiefly electrostatic repulsion from charged surfaces and steric repulsion from adsorbed layers, keep them apart against attractive van der Waals forces; when these repulsions are reduced the particles aggregate and the dispersion is destabilized.