Introduction to the basic knowledge of the most po

2022-07-31
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Introduction to basic knowledge of ink additives (VII)

Xi. Surfactants

surfactants are more and more widely used. Therefore, their varieties have reached an uncountable number. In the 1930s, there were only dozens of varieties, and in the 1970s, there were several dry varieties

it is no exaggeration to say that at present, all walks of life are inseparable from surfactants. The use of surfactants in printing ink, coatings, pigments and other related industries has a long history

(I) definition

surfactant refers to the general name of various compounds for various purposes, such as emulsifier, foaming agent, wetting agent, detergent, etc., which are all surfactants

surfactant can be defined as a substance that dissolves and concentrates on the surface of a liquid or the interface between a liquid and an immiscible liquid (or solid). Surfactants are those that are soluble in liquid components or mixed with powdered solids so that they can be easily wetted by liquid

simply speaking, surfactants are substances that act on the surface or interface of liquid liquid, liquid solid and liquid gas (generally speaking, the tension between the phase interfaces of objects is collectively referred to as interfacial tension, and the tension between the phase interfaces of liquid gas is specifically referred to as surface tension). It is a kind of auxiliary agent that can be adsorbed on the liquid surface or the water oil (or liquid solid) interface after being added to the liquid in a small amount, so as to reduce the surface tension and interface tension of the liquid and greatly improve the production process and product quality

most of the data about surfactants are about aqueous systems, generally speaking, they reduce the surface tension of water and the ability of water-soluble substances to form soluble micelles

surfactant is an organic compound. From the perspective of molecular structure, there are two groups: one is easy to dissolve in oil; The hydrophobic group (hydrophobic group nonpolar), which is a group insoluble in water, is represented by long-chain alkanes. The other is hydrophilic group (hydrophobic group polarity), which is easy to dissolve in water and difficult to dissolve in oil, and atomic groups represented by hydroxyl, carboxyl, amino, sulfate, sulfonate, ether, etc

according to the balance of hydrophilic group and lipophile group of surfactant (i.e. h.l.b. value - hydrophile liphilebalanc.) Relationship, surfactant manufacturers can produce countless products with different oil solubility and water solubility

generally speaking, although surfactants can be dissolved in liquid, their solubility is not high. They have a balanced polar nonpolar structure, that is, some molecules are dissolved in polar liquids, while others are in nonpolar liquids. The molecular layer is oriented and concentrated on the liquid surface, so the molecules of the dissolved part are in the liquid, and the insoluble part is in the air. This is the case with the monolayer of oleic acid on the water surface. If the benzene solution of oleic acid is placed on the water surface, the oleic acid will form a monolayer after benzene evaporation, and the carboxyl group is in water while the oleic acid group is in air. If oleic acid is spread on the oil surface, the opposite directional effect will occur

if you compare oleic acid (c17h33cooh) with soap or sodium oleate (C17H33COONa), you will find that there are differences. The non-polar oleic acid groups (C17H33COO -) between them are the same. However, sodium is more polar than hydrogen, so soap is soluble in water but insoluble in benzene and oil, while oleic acid is soluble in benzene and oil but insoluble in water

a very simple directional action diagram of surfactant on the liquid surface and the liquid-solid interface. As the wear pressure of many materials in practical use is variable, in fact, the effect of surfactant is related to the relative polarity of the polar non-polar part. In many cases, the surfactant layer does not necessarily form a single layer, but the molecular thickness is different, which depends on the amount and type of surfactant

of course, not all its molecules are at the interface, and its equilibrium between solution and interface also depends on its dosage. When the amount of surfactant with great configuration sensitivity reaches the critical concentration, it will form micelles, or the directional groups of its molecules in the whole liquid. Because micelles can absorb insoluble molecules, micelles are a kind of dissolving agent for ordinary insoluble molecules. The figure also shows the molecular arrangement of emulsifier in oil emulsion in water, including single layer and multi-layer

if there are more layers of emulsifier outside the droplets of the dispersed phase, the stability is better than that of only one layer. These micelles will increase the consistency of water and reduce the Brownian motion of dispersed droplets, so as to reduce the tendency of aggregation and make dispersion (emulsification) more stable

surfactants have many functions, such as emulsification, demulsification, foaming, foam stabilization, defoaming, wetting, dispersion, net washing, softness, leveling, antistatic, sterilization. Their performance directly affects the service life, rust prevention, corrosion inhibition, lubrication, solubilization, flocculation, deflocculation, anti floating and so on of high-speed rail lines

(II) classification

there are many classification methods for surfactants, but the commonly used method is to classify them by ion type, which means that when surfactants are dissolved in water, they can ionize to form ions, which is called ionic surfactants, on the contrary, they are called non-ionic surfactants. In ionic surfactants, they should also be classified according to the type of ions generated, for example:

1. anionic surfactants. Its active component is anion (negative charge), which can attract the positive charge of other macromolecules and leave negative charge on the surface, so that the water system has good wettability. The nonpolar part is fatty acid hydrocarbon chain; Anions and their associated cations are polar parts. When this kind of active agent is dissolved in water, the hydrophilic group connected with its hydrophobic group is anion

therefore, if polar pigments are dispersed in the non-polar binder, the polar part will be adsorbed on the pigment surface as a single molecular layer, making the pigments have negative charges, while the non-polar part will extend outward into the binder to form a state of mutual attraction. This process is the process of decreasing the interfacial tension. The electric double layer around the pigment particles also has the tendency to reduce flocculation. Soaps, alkali metals, ammonium salts and long-chain fatty acids are anionic

2. cationic type. In contrast to the anionic type, the positive charge attracts the negative charge, which is most suitable for the pigment dispersed in the binder. If the pigment is a positive charge, it can be well dispersed in non-aqueous systems. When this kind of active agent is dissolved in water, the hydrophilic group connected with its hydrophobic group is cation

quaternary ammonium salts of fatty acids or their sulfates and acetate belong to cationic type

3. amphoteric surfactant. The so-called amphoteric surfactant, in a broad sense, is the general name of surfactants with two ionic properties that have anions, cations, or both non-ionic and cationic, or non-ionic and anions. However, the amphoteric surfactants used to refer to the first type, that is, the surfactants composed of anion and cation. There are two ions with opposite properties in its structure, so it is noteworthy. Alkyl dimethyl internal ammonium salts belong to this category

4. non ionic type. This category belongs to surfactants that do not ionize in water. They have no residual charge, and some of the molecules are hydrophilic and some hydrophobic. Polyethoxylated phenols are non-ionic

5. other polymer type. This kind of surfactant has relatively high molecular weight, in which anions and cations are in equilibrium with each other, or at least approximate. Therefore, although it has strong ionic properties, it does not have the adsorption effect like the real anionic or cationic surfactants

(III) balance between hydrophilicity and hydrophobicity

the solubility of surfactants in water, that is, the so-called hydrophilicity (i.e. h.l.b.) value, is very important. Therefore, the ratio of hydrophilicity of hydrophilic groups to hydrophobicity of hydrophobic groups is an important indicator related to the performance of surfactants. Because the attraction or repulsion of a solvent (or liquid) to a compound and its aggregation effect at the interface depend on the relative polarity of hydrophilic and hydrophobic groups in the molecule

the relationship between the water solubility of surfactants and their properties is based on emulsification chemistry. According to the emulsification situation, someone proposed a classified data system, namely the so-called h.l.b. value of hydrophile and hydrophobic equilibrium

1. emulsification. Put the oil and water together in the container, then the oil is on the upper layer (with small specific gravity) and the water is on the lower layer, forming an obvious contact film at the boundary. Even after strong mixing, it will be divided into two layers slowly. For example, some surfactants (soap, detergent, etc.) are added to it, and then stirred and mixed, which becomes another situation. The oil is dispersed in water as tiny particles in the form of emulsion. This phenomenon is called emulsification. This emulsion is difficult to separate after standing

if the amount of emulsifier is increased and the amount of oil is reduced, the oil will be dissolved in water as a transparent solution. This phenomenon is called solubilization

the immiscibility of oil and water is caused by their different surface tension (for example, the surface tension of water is 72.8 dyne/cm (20 ℃), and the surface tension of oil is about 33 dyne/cm). The contact surface of oil and water has two functions: mutual exclusion and minimizing their contact area. Therefore, only when the oil and water are separated into two layers, Jinan experimental machine factory will introduce to you what are the high-strength bolt test clamps? The contact surface is the smallest, which is the most stable. If the mixture is stirred, the oil will become small particles dispersed in the water, which will increase the contact area between oil and water and make the system in an unstable state. Once the mixing stops and the mixing effect disappears, they restore the contact area to the minimum state and divide it into two layers. Emulsification and solubilization will occur when emulsifiers are added, because surfactants are composed of lipophilic groups that are soluble in oil and hydrophilic groups that are soluble in water. These two groups not only have the function of preventing mutual exclusion between oil and water, but also have the function of connecting oil and water

there are two methods for emulsification, one is called dispersion method and the other is called condensation method. The latter is the so-called lotion of nail benzene in water. It is formed by dissolving benzene in ethanol, and then pouring the mixture into water. The diameter of the emulsion droplets formed by this method is about one micron. It has no industrial significance

it is customary to use the dispersion method

the so-called emulsification means that one liquid is dispersed into fine particles in another immiscible (miscible) liquid. A layer of film is wrapped between the dispersed particles to prevent the aggregation of particles and make the lotion more stable. This kind of material that makes the lotion stable and prevents particles from agglutinating is called emulsifier

lotion is a system (system) composed of continuous phase (also known as external phase dispersant), dispersed phase (also known as internal phase dispersant) and emulsifier

lotion can be divided into two phases: oil in water (O/w-oilinwater) and water in oil (w/o-waterinoil-water in oil). The so-called O/W type means that water is a continuous phase and oil is dispersed into fine particles. The so-called w/O type means that oil is continuous

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