Correlation between emulsion stability and surface tension.

Emulsion refers to a dispersion system formed by a liquid that is dispersed in one or more liquid beads in a form that is not insoluble.
is called emulsion due to the system's milky whiteness, and the process of forming emulsion is called emulsification.
emulsion system, in the form of liquid beads, a phase is an internal phase, also known as a discontinuous phase or dispersed phase, and another connected into a piece called foreign or continuous phase, dispersed media.
most emulsions, one phase is aqueous solution (water phase), one phase is an insoluble organic matter (oil phase). The types of
emulsions usually have the following: (1) water-wrapped oil type (o/w): the inner phase is oil, the foreign is water.
such as: human milk, milk (2) oil-packed water type (w/o): the inner phase is water, the foreign minister is oil.
such as: oily cosmetics (3) ring type: by the water phase and oil phase layer of one layer of alternating formation of emulsion production emulsion production the most important step is from thousands of different commercial emulsifiers to choose the right emulsifier, emulsifier selection is generally anion active surfactant and non-ion surfactant or a combination of the two. the choice of
emulsifier is influenced by a variety of factors, first based on the type of emulsion (water-wrapped oil or oil-packed water), and the emulsifier must be adapted to the oil and water phase ingredients.
the second choice of emulsifiers also have certain principles, because the selected surfactant is multi-functional, its ability to emulsion, the type and stability of the emulsion produced is not only related to the type and concentration of the surfactant, but also related to the distribution of the various components in the system.
some of the principles for choosing surfactants in emulsifiers are described below.
(1) have a higher surfactivity in the system being applied and produce a lower interface tension, which means that the surfactant must have a tendency to migrate to the interface and not remain in the liquid phase on both sides of the interface.
, therefore, the hydrophilic and oil-related portion of the surfactant is required to have the proper balance, which will cause some degree of deformation of the structure of the two phases.
too much solubility in any one phase is disadvantageous.
(2) on the interface must be through their own adsorption or other adsorption molecules to form a fairly strong adsorption film.
from the requirements of molecular structure, there should be a large lateral interaction force between molecules on the interface, which means that in O/W type emulsion, the pro-oil base on the interface membrane should have a strong lateral interaction.
(3) surfactants must migrate to the interface at a certain speed, so that the interface tension of the system in the emulsification process can be reduced to a low value in time.
the speed at which a particular emulsifier or emulsifier system migrates to the interface is changeable and is related to the oil or water phase that is added to the emulsifier before emulsification.
emulsion makes the thermodynamic unstable system, disperses the phase spontaneity, reduces the boundarea, thus reducing the tendency of system energy.
lower oil-water interface tension contributes to the stability of the emulsification system.
combined with specific examples show that low oil-water interface tension is beneficial to the stability of emulsifiers. There are many test methods
oil-water interface tension, which are common in the selection of rotary drop analysis method, Whilhemy sling method and drop volume method.
here is a probe-type surface tension analyzer (Kibron EZ-PIPLUS) based on the Whilhemy sling method to test oil-water interface tension, which has a sophisticated analytical balance (0.2ug) that, in addition to testing some conventional oil-water interface tension, can also test some samples with low oil-water interface tension (0-10mN/m) and have a simple operation.
an experiment on the correlation between interface tension and the stability of emulsifiers.
first test paraffin oil water system interface tension: ow s 41mN/m, the paraffin oil water system mixed and dispersed into the corresponding emulsion, the emulsion solution is unstable; The emulsion system obtained by the preparation of the mixture into a mixing system is still unstable, and the oil-water interface tension tested after adding NaOH and sodium olelate is significantly improved in the o/w emulsion at this time.
, the stability of emulsifier and the surface activity of the selected emulsifier are related, in general, high-performance surfactants can reduce the interface tension of oil and water, thereby reducing the interface energy of the system, because the interface tension is the root cause of the thermodynamic instability of emulsion, so the reduction of interface tension is conducive to the stability of the emulsion.
of course the stability of the emulsion also need to ensure that the added emulsifier concentration is greater than its critical beam concentration (CMC), so as to ensure that there are enough emulsifier molecules can be adsorbed on the oil-water interface, forming a high-strength interface film.
the stability of the emulsifier is also related to the hydrophilic-oil-affinity balance (HLB) value of the selected emulsifier and the interface charge of the emulsion forming, the greater the charge density of the droplet surface in the emulsion system, the higher the stability of the emulsion.
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