Emulsion properties and characteristics, types, receiving, and destruction.
An emulsion is a disperse system, i.e. a mixture of a number of phases (bodies), is not able to dissolve in each other or interact at the level of chemical processes, and therefore persist in the form of fine droplets.
The emulsion, which translated from Latin means “milk”, “milk” – a mixture comprising two or more liquids that do not mix with each other.
If expressed in scientific language, the emulsion is a disperse system, i.e. a mixture of a number of phases (bodies), is not able to dissolve in each other or interact at the level of chemical processes, and therefore persist in the form of fine droplets. In the classical two-phase emulsions are dispersed:
– phase – the smallest particles of a certain liquid substance;
environment – the fluid in which the phase is uniformly distributed.
Usually a mixture is a compound of water and substances based molecules with weak polarity (lipids, carbohydrates). So, striking a classic example of an emulsion is milk – a mixture of water and milk fat evenly distributed in it.
Mixes are mostly dispersed systems ill-nature, since the size of the droplets, representing the phase, ranges from 1 to 50 micrometers. If their concentration is low – it speaks of an unstructured nature, high – availability of a clear structured system.
In addition to the concentration and the dispersion, another key characteristic of an emulsion is its stability over time, and aggregate stability and the presence of emulsifiers. All these factors allow us to estimate its ultimate properties.
The dispersion of the emulsion:
The dispersion emulsion measured in the particle size of the phases, expressed in micrometers and is usually in the form of a histogram.
The stability of the emulsion over time:
This parameter stability in time – can be expressed in two forms:
the speed with which the emulsion to delaminate. The mixture is left for a certain time after the emergence of two different layers, measure the height or the volume snabpolimer phase;
– time “live” individual drops. Used the method of observation under a microscope, where snabpolimer drop of liquid is placed on the border components, and then recorded the time required for merging them.
In practice, most used the first method as less costly and more simple.
The concentration of the emulsion:
Concentration is one of the major parameters determining the final properties of the emulsion, based on which further classification of mixtures. Accordingly, the emulsions may be:
– highly concentrated.
The aggregative stability of the emulsion:
The aggregative stability of the emulsion – another property indicating the ability to save in the time interval of primary droplet sizes that comprise the disperse phase. Accordingly there are three types of emulsions:
– electrostatic emulsion. The corresponding field is formed around the droplets forming the emulsion, resulting in an energy barrier which prevents particles to get close to the moment when the force of attraction exceeds the electrostatic repulsion;
– adsorption-solvate emulsion. The surface tension arising at the boundary of a medium and the phase decreases due to the emulsifying agents, which adsorb on the surface of droplets, which makes the mixture more stable;
– structural-mechanical emulsion. In this case, the emulsifier molecules form a rather dense layer on the surface of the non-dissolving drops that prevents them from merging with the environment due to increasing viscosity and elasticity.
Often one of these types is the main and the rest secondary.
The presence of emulsifiers:
Sustainability also depends on the choice of the emulsifier whose main task is to reduce or minimize the energythat is present at the interface of environment and phases, and how densely covered the surface of the emulsion emulsifiers.
Emulsifiers – substances that ensure the creation of emulsions from immiscible liquids. Their presence is necessary for the sustainability of concentrated mixtures. They can be:
– inorganic electrolytes;
high molecular substances;
– finely divided insoluble powders.
The main separation of mixtures of the types is characterized by such a parameter, the polarity of the dispersed phase and the medium. This:
– direct (“oil-water”) emulsion of the first kind, where a non-polar mass (usually a lipid) is distributed in the water;
– reverse (“water-oil”) emulsions, of type II, where water is a phase, distributed in a non-polar environment (oil).
When determining the type of emulsions using the Bancroft rule – dispersion medium is the liquid part of the emulsion, which dissolves better emulsifier or better it wets, if it is a powder. However, there is an exception – it is 100% rule works only in the case when the compound has no more than two components.
In other situations, the use of experimental methods of determining the type of emulsion:
1. Dilution. A drop of emulsion is placed in a container of water: if it is not distributed in the vial, it says the type “water-oil”.
2. The wetting of hydrophobic surfaces. When applying a drop of emulsion on a plate of paraffin wax when you type “water-oil” drop starts to spread.
3. The definition of the continuous phase. Next to drop put the crystals are water-soluble dyes and connect the substance in the presence of a mixture of “oil-water” it is not stained. To confirm the results of a repeated experience with fat-soluble dyes.
4. The measurement of electrical conductivity. The mixture was placed in the electrodes and the neon lamp will light if the latter, it means that the type of emulsion is an “oil-water”, because water has a higher conductivity than oil.
Also formulas are divided into:
– freeze – those that are formed independently and have the resilience to thermal effects. Usually the so-called critical emulsions, encountered in places at high (critical) temperatures of the mixed liquid of the dispersed phase;
– lyophobic – formed during decomposition of solid particles into smaller components (emulsifying) under the influence of mechanical, acoustic or electrical factors or as a result of condensation in solutions and alloys with high saturation.
A distinctive feature of lyophobic emulsions lack of resistance to thermal stress and the possibility of long-existing exclusively in the presence of emulsifiers.
Any mixture comprising two immiscible liquids is in a state resistant to thermodynamic forces, but only until such time as both are solid layer: a lighter top and heavier at the bottom. In that moment, when one of these layers start to be fragmentation, increased interfacial layer consisting of a mixture of two liquids that leads to a decrease in thermodynamic stability. Thus the more energy will be spent on obtaining the emulsion (mixing layers), the less stable it will become. In order to increase the last parameter and use the emulsifiers present in all mixtures except those that are formed independently. Consequently, almost any emulsion is a three-component fluid, one of which is represented by drops.
For each particular emulsion droplets must be of a certain size, and their preparation is done by two methods:
– condensation when droplets grow from small size to fit;
– disperazione the crushing of large drops to small.
Condensation from the steam. The vapor of the liquid, which will become the disperse phase, is injected under the surface of the other forming in the future dispersion medium. In the result, the steam becomes saturated with molecules of the second liquid and in the form of condensation desired size stabiliziruemost in the environment with the help of the emulsifier.
Depending on how pressure will be supplied steam, and the size of the discharge nozzle (diameter) of the stabilizer selected and will be able to receive drops from 1 to 20 micrometers.
Replacement of the solvent. A substance selected as the phase of the future emulsion is subjected to dissolution in a certain solvent (“good”), which allows to obtain the true solution. When you try to enter in the mixture other solvent which does not interact with the first and spoiling it, you get the opposite effect – a previously dissolved substance will once again be “going to” in the drops.
The mechanical method. Is the direct impact on selected fluid for uniform mixing by crushing larger particles into smaller ones. This can be a classic blending, vigorous shaking, homogenization and so on.
Shake usually does not require special devices, as used to obtain small volumes and is carried out manually: the container or vial are taken in hand and vigorously shaking (for example, for chemical experiments). Mixing and also allowed for large amounts of mixtures (in the industry), so some of them use special devices and mechanisms. Homogenization is a complete technological process that requires special equipment. In this emulsification is carried out by passing the mixed fluids through small apertures under high pressure.
The application of ultrasound. The technique consists of exposing a mixture of high frequency (20-50 kHz), therefore, implies the presence of specialized equipment.
Electric techniques. Complex, but the most commonly used method, has a number of advantages. When using it the substance to be crushed is placed in a special vessel, which is crowned by a capillary funnel. The latter is connected to a source of current (positive charge). The container shall be grounded using the premises in a flask with a round bottom, where there is a grounded electrode. The flask is placed in the fluid, which in the future the emulsion will be dispersed medium, and the mixture is formed by the method of connection drops flowing from the crater, under the influence of electric current.
The size of the particles in this method are governed by the size of the gap between the funnel and the liquid and the voltage, and can reach 1-10 micrometers. To improve the stability of the emulsion can introduce the emulsifier, but large quantities are required. This is the main advantage of the method is possibility to obtain a comparatively stable emulsions of both types with a high monodispersity. Among the shortcomings allocate the impossibility of introduction of the emulsifier in the mixture too viscous.
Spontaneous emulsification. Is the formation of mixtures that do not require energy costs, coming from the outside, for example, in contact of two substances in the zone of critical temperature.
The demulsibility is as important process as the creation of the emulsion. The destruction of the obtained mixtures is achieved by two methods: sedimentaria (sedimentation) and coalescence.
In real emulsions the final, complete destruction does not occur, and creates two separate emulsions, and in one the concentration of the dispersed phase is high and the other low. Larger drops and heavy phase sink to the bottom easier environment (upsetting). In order for this process to go faster on the companies use of a centrifuge.
Coalescence is a process in which a mixture is separated into a separate clean fluid. Separation occurs in two stages:
1. flocculation – the process by which a substance that is a phase, turns into a loose, cotton particles, easily dissolved even at a weak stirring of the emulsion;
2. directly separation is formed in the first stage, particles as large drops, easily allocated in a separate substance. Thus destroy the resulting aggregates and emulsions to return to original condition is almost impossible, it requires a very intensive mixing.
There are several techniques of destruction of emulsions, what they can be used both individually and in combination.
There are two ways:
– removal of barriers, a kind of film between the layers of the mixture that prevents them from mixing. The use of special chemical substances allows to neutralize this protection, literally dissolving film barriers;
– treatment of the emulsion. The use of substances considered to be placed in a reverse emulsion, the emulsifier neutralizes the effect of the latter.
By two opposite ways:
– fever – is to bring the emulsion to its high critical temperature (each mix is its own) and subsequent settling. The method is based on the fact that the chemical reaction of certain substances increase, which affects the viscosity of the mixture and the composition of the barrier layer;
– if the temperature – in this case by freezing the water part of the emulsion is transformed into crystals, and oil – compressed. If the desired fluids contain salt, they too can turn into crystals that, together with water, “tear” protective film, which does not allow major components to be mixed.
Deposition with the use of physical force:
Based on the action of gravity and centrifugal force:
– settling mixture composed of large, coarse oil phase is placed in a special sedimentation tanks is not less than 1 hour, more fine and soft particles remain in suspension;
– the use of centrifuges – with the rapid rotation of the components with greater severity, shifted (repelled) to the periphery, while the lighter components are concentrated in the center. The technique is more common because it gives the opportunity to interact with large volumes of emulsion for a short period of time – the result is achieved within a few minutes.
These methods are only effective for the two types of emulsions:
– those that contain charged particles;
– electrically neutral, but capable to acquire an additional dipole moment that is induced in the electric field.
This method requires the availability and use of specialized equipment, so rarely used.
The emulsion is a rather complex chemical compound, but it has found application in almost all modern industries. First and foremost, it’s food – mayonnaise, various sauces, butter, and cosmetics – shampoos, products for removing make-up and skin care – all types of emulsions. Essential emulsion in the automotive and construction industries – engine oil, cooling and brake fluids, adhesives and bituminous materials. Also worth noting is the pharmacy – many drugs designed to strengthen health and to save human life are emulsions and what most people don’t even think.
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