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Lecture

Surface Tension and Surfactants

In course

ME-271: Fluid flow

Dans ce cours introductif à la physique des fluides, l'étudiant commence par apprendre, au moyen de bilans de masse et de contraintes, à décrire et à prédire les écoulements types. Ces méthodes sont appliquées à des écoulements complexes, tels que les écou ...

Description

This lecture discusses the effects of adding an ice cube to water, including changes in surface tension and the movement of surfactant molecules. It also covers the variation of surface tension due to the concentration of surfactants and the phenomenon of capillarity at liquid interfaces.

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Instructor

Karen Ann J Mulleners

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Related concepts (6)

Surface tension

Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged. At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). There are two primary mechanisms in play.

Surface energy

In surface science, surface free energy (also interfacial free energy or surface energy) quantifies the disruption of intermolecular bonds that occurs when a surface is created. In solid-state physics, surfaces must be intrinsically less energetically favorable than the bulk of the material (the atoms on the surface have more energy compared with the atoms in the bulk), otherwise there would be a driving force for surfaces to be created, removing the bulk of the material (see sublimation).

Capillary action

Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube such as a straw, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a biological cell.

Interface (matter)

In the physical sciences, an interface is the boundary between two spatial regions occupied by different matter, or by matter in different physical states. The interface between matter and air, or matter and vacuum, is called a surface, and studied in surface science. In thermal equilibrium, the regions in contact are called phases, and the interface is called a phase boundary. An example for an interface out of equilibrium is the grain boundary in polycrystalline matter.

Tension (physics)

In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as the action-reaction pair of forces acting at each end of said elements. Tension could be the opposite of compression. At the atomic level, when atoms or molecules are pulled apart from each other and gain potential energy with a restoring force still existing, the restoring force might create what is also called tension.

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Gas-Liquid Interface: Forces, Pressure, and Curvature

Covers forces, pressure, and curvature at the gas-liquid interface, including vapor pressure, wetting, and surface tension measurements.

Thermodynamics of Interfaces: Gibbs Model and Micelles

Explores the Gibbs model of interfaces and micelle formation in surfactant solutions.

Liquid Crystals: Structure and Properties