Surface rheology
Encyclopedia
Surface rheology is a description of the rheological properties
of a free surface
. When perfectly pure, the interface between fluids usually displays only surface tension
. But when surfactant
s are adsorbed on the interface, because they lower the surface tension, the stress within the interface is affected by the flow for several reasons.
) of dispersed media
such as liquid foams and emulsions is strongly affected by surface rheology. Indeed, when, they consist in two (or more) fluid phases, deforming the material implies deforming the constitutive phases (bubbles, drop
s) and thus their interfaces
.
Rheology
Rheology is the study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force....
of a free surface
Free surface
In physics, a free surface is the surface of a fluid that is subject to constant perpendicular normal stress and zero parallel shear stress,such as the boundary between two homogenous fluids,for example liquid water and the air in the Earth's atmosphere...
. When perfectly pure, the interface between fluids usually displays only surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
. But when surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s are adsorbed on the interface, because they lower the surface tension, the stress within the interface is affected by the flow for several reasons.
- Change in the surface concentration of surfactants when the in-plane flow tends to alter the surface area of the interface (Gibbs' elasticity).
- AdsorptionAdsorptionAdsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
/desorptionDesorptionDesorption is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption . This occurs in a system being in the state of sorption equilibrium between bulk phase and an adsorbing surface...
of the surfactants to/from the interface.
Importance of surface rheology
The mechanical properties (rheologyRheology
Rheology is the study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force....
) of dispersed media
Dispersed media
A dispersed medium consists of two media that do not mix. More specifically, it contains discrete elements of one medium which are dispersed in a continuous second medium. The two media can be of very different nature. In particular, they can be a gas, a liquid or a solid.Many materials which we...
such as liquid foams and emulsions is strongly affected by surface rheology. Indeed, when, they consist in two (or more) fluid phases, deforming the material implies deforming the constitutive phases (bubbles, drop
Drop
-General use:*Drop or droplet, a small volume of liquid**Eye drops, saline drops used as medication for the eyes*Drop , a unit of measure of volume*Falling , or allowing an object to fall...
s) and thus their interfaces
Free surface
In physics, a free surface is the surface of a fluid that is subject to constant perpendicular normal stress and zero parallel shear stress,such as the boundary between two homogenous fluids,for example liquid water and the air in the Earth's atmosphere...
.