Creaming (chemistry)
Encyclopedia
Creaming, in the laboratory
sense, is the migration of the dispersed phase of an emulsion
, under the influence of buoyancy
. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how thixotropic the continuous phase might be. For as long as the particles remain separated, the process is called creaming.
Where it is important that either the form or the concentration of the emulsion should be stable, it is desirable that the continuous and the dispersed phases should have similar densities, and it also is desirable that the continuous phase should be viscous or thixotropic. Thixotropy
is particularly valuable in paints, sauces, and similar products, partly because it counteracts tendencies towards creaming. It also is important that the particles be as small as practicable because that reduces their tendency to migrate under the influence of buoyant forces. The electric charges on their surfaces should preferably tend to be uniform, so that the particles repel rather than attract each other.
Creaming is usually seen as undesirable because it causes difficulties in storage and handling, but it can be useful in special cases, especially where it is desirable to concentrate an emulsion. A particular example is in the separation of dairy cream, either to achieve a desired concentration of butterfat
, or to make butter
.
Depending on whether the dispersed particles are less dense or more dense than the continuous phase, they may move either to the top of a sample, or to the bottom. As already stated, the process of migration is called creaming while the particles of the substance remain separated. In this it differs ideally from flocculation
(where particles clump) or emulsion breaking (where particles coalesce). One important difference between creaming and the other two processes; unlike flocculation and breaking, creaming of an emulsion is largely a simple process to reverse.
due to the close proximity of the globules in the cream. Factors that influence the rate of creaming are similar to those involved in the sedimentation rate of suspension particles, and are indicated by Stokes Law
.
Creaming of an emulsion also increases the tendency of an emulsion to inversion. This class of process occurs mainly in special cases, when both the continuous and dispersed phases of an emulsion are liquid, as commonly is the state in dairy cream. It is common where the volume of the two fluid components is about the same or the volume of the dispersed phase is larger than that of the continuous phase. The process of emulsion inversion occurs when the dispersed droplets unite, but retain the formerly continuous material as droplets within the mass.
This is an "invert emulsion" or "inverted emulsion", in which the formerly continuous phase has become the dispersed phase and vice versa. Inversion happens in dairy cream when the butterfat concentration is too high, and the resulting invert emulsion looks much like butter.
Commonly invert emulsions look much like a paste or thick cream, and typical examples are mayonnaise, margarine (especially "low-fat" grades of margarine), similar creamy foods, pharmaceutical ointments, and cosmetic "creams".
Emulsion inversion differs from emulsion breaking in that a breaking emulsion tends to separate the two phases into un-emulsified continuous phases. Inversion of an emulsion may or may not be difficult to invert, but generally more difficult than creaming.
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...
sense, is the migration of the dispersed phase of an emulsion
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
, under the influence of buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how thixotropic the continuous phase might be. For as long as the particles remain separated, the process is called creaming.
Where it is important that either the form or the concentration of the emulsion should be stable, it is desirable that the continuous and the dispersed phases should have similar densities, and it also is desirable that the continuous phase should be viscous or thixotropic. Thixotropy
Thixotropy
Thixotropy is the property of certain gels or fluids that are thick under normal conditions, but flow over time when shaken, agitated, or otherwise stressed...
is particularly valuable in paints, sauces, and similar products, partly because it counteracts tendencies towards creaming. It also is important that the particles be as small as practicable because that reduces their tendency to migrate under the influence of buoyant forces. The electric charges on their surfaces should preferably tend to be uniform, so that the particles repel rather than attract each other.
Creaming is usually seen as undesirable because it causes difficulties in storage and handling, but it can be useful in special cases, especially where it is desirable to concentrate an emulsion. A particular example is in the separation of dairy cream, either to achieve a desired concentration of butterfat
Butterfat
Butterfat or milkfat is the fatty portion of milk. Milk and cream are often sold according to the amount of butterfat they contain.- Composition :The fatty acids of butterfat are typically composed as follows :...
, or to make butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...
.
Depending on whether the dispersed particles are less dense or more dense than the continuous phase, they may move either to the top of a sample, or to the bottom. As already stated, the process of migration is called creaming while the particles of the substance remain separated. In this it differs ideally from flocculation
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...
(where particles clump) or emulsion breaking (where particles coalesce). One important difference between creaming and the other two processes; unlike flocculation and breaking, creaming of an emulsion is largely a simple process to reverse.
Creaming
A Creamed emulsion increases the likelihood of coalescenceCoalescence
Coalescence may refer to:* Coalescence , the merging of genetic lineages backwards time to a most recent common ancestor* Coalescence , the merging of two or more phonological segments into one...
due to the close proximity of the globules in the cream. Factors that influence the rate of creaming are similar to those involved in the sedimentation rate of suspension particles, and are indicated by Stokes Law
Stokes law
Stokes' law can refer to:*Stokes' law for friction force*Stokes' law law describing attenuation of sound in Newtonian liquidsFor integration, see Stokes' theorem....
.
Creaming of an emulsion also increases the tendency of an emulsion to inversion. This class of process occurs mainly in special cases, when both the continuous and dispersed phases of an emulsion are liquid, as commonly is the state in dairy cream. It is common where the volume of the two fluid components is about the same or the volume of the dispersed phase is larger than that of the continuous phase. The process of emulsion inversion occurs when the dispersed droplets unite, but retain the formerly continuous material as droplets within the mass.
This is an "invert emulsion" or "inverted emulsion", in which the formerly continuous phase has become the dispersed phase and vice versa. Inversion happens in dairy cream when the butterfat concentration is too high, and the resulting invert emulsion looks much like butter.
Commonly invert emulsions look much like a paste or thick cream, and typical examples are mayonnaise, margarine (especially "low-fat" grades of margarine), similar creamy foods, pharmaceutical ointments, and cosmetic "creams".
Emulsion inversion differs from emulsion breaking in that a breaking emulsion tends to separate the two phases into un-emulsified continuous phases. Inversion of an emulsion may or may not be difficult to invert, but generally more difficult than creaming.