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1、胶体与界面化学小论文（Small papers on colloidal and interfacial chemistry）Introduction to Colloid and Surface Chemistry chapter 10 Emulsions and foams keywords: Emulsions; Foams this chapter firstly introduces some basic concepts of emulsion, first of all, the definition of emulsion (1) emulsion is a dispersio
2、n system consisting of several liquids which are completely insoluble or partially intersoluble. Generally speaking, such a system must have a relative stability or equilibrium destruction can be stratified or settled. Of course adding surfactant or using some other method can increase this stabilit
3、y. Now that is dispersed system, there is a different dispersed phase, generally speaking, in the form of liquid bead is suited for internal phase and dispersed phase or discontinuous phase, relative does not exist in the form of phase is the foreign minister, dispersing medium, or continuous phase.
4、 Dispersed phase droplets in the 0.1 mu m 10 microns in diameter, larger than the aerosol particles, but now also made from the micro emulsion, the droplet particles in 0.01 0.1 microns, is used in the tertiary oil recovery, the micro emulsion is between plus sol group and emulsion of a system. Beca
5、use of this, there are two kinds of theory of mixing membrane and solubility in the formation of microemulsion. Hybrid membrane theory, the theory is that the micro emulsion is the emulsion droplet tiny, the causes of the formation of micro emulsion can spontaneously, is a mixture of surfactant and
6、help surfactant film can be formed on the surface of the oil - water boundary temporary negative interfacial tension. The microemulsion is formed by the fact that the micro-emulsion type gamma I has a surfactant and the oil-water interfacial tension of the surface active agent. (gamma o/w) a is the
7、oil-water interfacial tension in the oil phase of the surfactant. PI is the oil - water interface pressure. If PI BBB 0 (gammas/w) a, gamma I is negative, the expanded interface is the system interface free energy drop process, so the microemulsion can spontaneously form. After the formation of micr
8、oemulsion, gamma I = 0, the system is in thermodynamic equilibrium. The function of the surfactant is to reduce (gammas/w) a and increase the PI, causing the gammas to be negative. This theory holds that the essence of microemulsion is the swelling gel, which is the result of the solubility of the s
9、olution under special conditions. The solubility is spontaneous, so the microemulsion can form spontaneously. The concentration of surfactant exceeds the critical concentration of micronic mass, which is the solubility, but the solubility of the surfactant is less than 10% (weight), which can form t
10、he microemulsion. The condition of forming a microemulsion is that the hydrophilic and hydrophilic properties of the surface active agent are close to the equilibrium. If the hydrophilic and hydrophilic oil of the surfactant is close to the equilibrium and slightly hydrophilic, it can form o/w micro
11、emulsion. In contrast, w/o microemulsion can be formed. The hydrophilic and hydrophilic properties of non-ionic surfactants can be adjusted by changing temperature or the length of ethylene oxide chain in the molecule. Ionic hydrophilic and lipophilic property of the surface active agent with the te
12、mperature change is not big, generally with help of surfactant to adjust, this is ion table surface active agent to form the micro emulsion must be joined to help the cause of the surfactants in oil phase. It is worth noting that there is not a small amount of internal phase, which is the external p
13、hase. In fact, it is now possible to make up to 90% of the emulsion. The droplets vary in size and the scattering of light is different. Generally less than 0.05 mu m liquid bead is transparent, at 0.05 0.1 mu m is gray translucent, at 0.1 1 mu m is blue and white emulsion, greater than 1 mu m is mi
14、lk white emulsion. Almost all the emulsion is water, and the other is oil. Because the internal and external phase are not divided into the O/W and the W/O in the water-covered emulsion. There are also heavy heavy ones such as W/O/W, O/W/O type. There are four ways to distinguish between O/W and W/O
15、. In general, the W/O type is more slippery than O/W. 2. Dilute the emulsion and pour the emulsion into the water. If it can be dispersed quickly, it will be O/W and vice versa. 3. Staining, the oil soluble dye is added to the emulsion, if the whole emulsion is dyed,Oil is the external phase. If onl
16、y the droplets are dyed, then the oil is the internal phase. (2, 3 methods can be explained by similar phase solution) 4. Electrical conductance method, generally speaking, O/W conductivity is greater than W/O conductivity. However, the W/O type of water content in W/O is relatively large or is an i
17、onic emulsifier and sometimes has high conductivity. And then the stability of the emulsion is a very important physical property. Because the emulsion is a highly dispersed unstable system with a huge interface, the system has high energy. So to keep the system stable you have to add the third comp
18、onent, the emulsifier. (emulsifier is an application of surfactant, which is used to stabilize emulsion). The emulsifying agent is formed around the droplet to form a layer of adsorption membrane which can prevent the condensation and coalescence of droplet. But the mechanism of action is very compl
19、icated. There are three main types: 1. The main purpose of adding surfactant is to reduce interfacial tension between oil and water. But the most important thing is to reduce the area of the interface to reduce the energy of the system. 2. Enhance the mechanical strength and elasticity of the interf
20、ace membrane. Adding surfactant can reduce the interfacial tension and also form adsorption membrane to protect the dispersed phase particles. Emulsion droplets in the surfactant in the thick degree to a certain extent, molecules are closely packed, adsorption film strength will get bigger, the resi
21、stance of the merger between the droplets is bigger, so is stable. When the surfactant concentration is low, the resistance of the droplets in the emulsion is small, and it is easy to coalesce and sink. So the emulsifier dosage should be sufficient to form a condensed film. Studies have shown that a
22、dding a small amount of fatty alcohol, fatty acids or fatty amines to the surfactant can improve the stability of the emulsion. So it is better to combine hydrophilic emulsifiers with a compound film. The explanation is that the surface active agent and the fatty alcohol form the molecular permutati
23、on in the mixed adsorption layer, improve the strength of the surface film, and can further reduce the interfacial tension. 3. The repulsive effect of the interface charge. When ionic surfactants are used as emulsifiers, the liquid drop interface is adsorbent to make the liquid oil emulsion interfac
24、e electrically charged. The electrostatic repulsion can obstruct droplet polymerization. Non-ionic emulsifier emulsion stability and water-in-oil emulsion often can be charged, explanation is that the oil phase dielectric constant is low, as long as there are a few ions can build very thick diffusio
25、n electric double layer, so it is stable. After mixing the two non-soluble liquids, which type of emulsion can be formed, it mainly depends on the relative size of 2 points: 1. In 1910, Ostwald proposed that the ball accounted for 74 percent of the volume, while the volume was greater than 74 percen
26、t of the volume and the volume was less than 26 percent. The range of 26-74% is arbitrary. But most of the time, the droplets of the emulsion are different in size, and the internal phase volume can be significantly higher than 74%, because the droplets can be unequal and the internal phase can be n
27、on-spherical. The inner phase volume can reach up to 90%, or even 99%. 2. Properties of emulsifier. Wedge theory, simple said is the comparison of emulsifier into two different sizes of wedge, the wedge to arranged closely, to the end of the cross section of small always points to the dispersed phas
28、e, relative to the end of the big cross section in dispersion medium. As a result, an O/W type, such as alkali metal soap, can be easily formed. In general, the two price, three price metal soap oil soluble strong, easy form W/O emulsion. But it is not certain, for example, when silver soap makes em
29、ulsifier, it forms W/O emulsion. In the two phases of the emulsion, where the emulsifier is more likely to dissolve in a phase, the phase is likely to become a dispersible medium. It is the solubility rule, introduce a concept, the partition coefficient is at certain temperature, emulsifier in water
30、 phase and oil phase solubility ratio should be constant. When the distribution coefficient is large, the O/W type can be easily obtained, and the W/O type is obtained. In order to find better emulsifiers,The HLB value has some reference value, but only provides a way to avoid blindness, which does
31、not mean good or bad. According to the HLB value, the success rate of finding suitable emulsifiers is increased. The maximum determination of the HLB value is that the temperature factor is not considered. The higher temperature will weaken the hydrophilicity of the emulsifier, and the HLB value wil
32、l decrease. In order to give consideration to temperature, the concept of HLB temperature is put forward. It is best to use the HLB value to determine the emulsion, and then test it with a PIT value. In the same way, the value of W/O type HLB is between 3 and 6, and the O/W type HLB value is between
33、 8 and 18. And if the HLB value is similar, the emulsifying effect of the hydrophobic base and the oil phase structure is good. It is worth noting that the electric shadow can make the emulsifying effect of the emulsified agent of the emulsion be good, and the emulsion is stable. The emulsifier char
34、ge cannot be the opposite of the original. Of course, when choosing emulsifiers, different emulsions should be selected for different needs, such as food is best non-toxic and tasteless, and the textile will not affect the subsequent process such as dyeing. Stable emulsion is what we want, but it ca
35、n also help to isolate and purify certain substances. The destruction of the emulsion, from the thermodynamics, is only the difference between the way and the time. The typical demulsification process is the process of stratification, variation and demulsification. Stratification is not a real destr
36、uction, it is divided into two emulsions, such as the layers of milk. Under the neutral action, the droplets float or sink, allowing the dispersed phase of a phase to be concentrated. The rate of stratification is related to the density difference between the two phases, the external viscosity and t
37、he droplet size. It can be accelerated by high speed centrifugation or by adding reagents. Variation refers to the type change of emulsion. The variation process is the process of the condensation of liquid droplets in the emulsion and the dispersion of dispersed medium. There are four main factors
38、that cause the emulsion change, 1) the change of emulsifier type. 2) the influence of phase volume. The volume above a certain number may cause the emulsion to change. 3) effects of temperature. The temperature rises, the hydrophilicity declines. The oil is on the rise. 4) electrolytes. Mainly ionic
39、 soap, when the concentration of electrolyte rises, the dissociation degree decreases and the hydrophilicity declines. Add electrolytes, water and oil phase, and some of the soap is precipitated out in solid form. And the solid filtration, the hydrophilic enhancement. Therefore, solid soap precipita
40、tion is the main cause of emulsion deformation. To achieve the breaking of the emulsion, the method can be added, high piezoelectric, displacement, filtration and other mechanical methods and addition of anti-emulsifier. The main content of the emulsion is the foam. A bubble is a crude dispersion of
41、 gases in a liquid. A gas is a dispersed phase, and a liquid is a dispersion medium. Foam is mainly divided into two kinds, one is the thin foam, the gas is dispersed evenly in the more viscous liquid with the small ball, the bubble surface has thicker film, even some people call it emulsion. The ot
42、her is that because the density of the gas is very different from that of the liquid, the viscosity of the liquid is relatively low, and the bubbles can rise rapidly to the liquid surface, forming a bubble aggregation. Bubble aggregates are composed of polyhedral bubble cells separated by a small li
43、quid membrane. The performance of foam mainly depends on the liquid film, so the study of liquid film performance is the main content of the bubble. To make the bubble stable you have to add a third component, the foaming agent. In general, good emulsions are also excellent foaming agents. The stabi
44、lity of a bubble depends mainly on two aspects - the flow of liquid in the liquid membrane and the size of the trend of thin film thinning and the tendency of the random disturbance that can cause the bubble to burst. 1) the liquid loss of liquid film in foam is mainly the result of the gravity and
45、air bubbles squeezing each other. The extrusion pressure results from the influence of van der Waals force and surface pressure between liquid molecules. The gas phase pressure in the foam is equal, but the curvature of the interface in the liquid membrane is the schematic diagram of the boundary pl
46、ane of the liquid membrane which represents the three bubbles. B pressure is higher than A, so the liquid flows to A, making the liquid film thin, and due to resistance, it balances out to A certain degree.Look from the surface pressure, when the Angle is 120 the most stable, pressure difference is
47、minimal. So in a polysexual foam structure, its usually a hexagonal structure. 2) the stability of the foam also depends on the ability of the liquid film to resist the partial overthin film and rupture of the membrane. This tolerance is influenced by many factors, mainly three. Gibbs - marango surf
48、ace elastic effect. Because the external disturbance causes the local surface area to increase, the surface tension of the local area increases - gibbs effect. But because of this, the neighboring bubbling agent spreads to the area and brings it back to its original state - the marangoan effect. Usu
49、ally these two effects can be balanced and maintain foam stability. This effect promotion, evo (Ewers) and Mr Voser rand (Sutherland) put forward the mechanism of surface transportation: thin liquid film giant formed by surface tension gradient will make frother along the surface diffusion, and with a fairly quantity under the surface of the solution, make the local thinning the thickness of liquid film and restore to the original. Surface rheology. Similar to the emulsion, mechanical properties have an effect on stability. High viscosity and surface elasmosis wi