Surfactants are widely used in cosmetics, food, medicine, pesticides and other industries, and play an extremely important role in the application, functionality and marketability of these industrial products. Unfortunately, we often know much less about the choice and mechanism of surfactants than other active ingredients. The term surfactant is often used interchangeably with the term emulsifier. A simple definition of a surfactant can be thought of as: it is a substance that changes the surface properties of other substances. Commonly used to reduce the surface tension of water (sometimes oil) and reduce the interfacial tension between water and oil. There are many ways to classify surfactants. The most common method is to ionize into ions according to the gate, ie anions, cations. , bisexual or non-ionic classification. Generally cationic surfactants are more expensive.
We know that in determining the suitability of a surfactant for various dosage forms, the chemical nature of the surfactant and its hydrophilic, lipophilic balance (ie, HLB value) are two essential contributing factors. The first factor is the choice of a nonionic surfactant when a cationic or anionic surfactant is present in the formulation. If a cationic surfactant is selected to be added to a formulation that already contains an anionic surfactant, the interaction of the anion and cation may result in precipitation. It is known in practice that these types of surfactants are incompatible in the formulation of pesticides such as organophosphorus. Therefore, in the processing of pesticide formulations, it takes a lot of work to develop a correct surfactant for a given pesticide. The second factor is that all surfactants have a water soluble (hydrophilic moiety) and an oil soluble (lipophilic moiety). Thus, in the presence of a surfactant, the oil and water can be mixed, the hydrophilic chain holding the water tightly, and the lipophilic chain holding the oil tightly to hold them together. The HLB value is a measure of the degree of hydrophilicity of the surfactant which gives the type of surface active or mixed active agent required to emulsify a particular oil. The HLB value is the value obtained by dividing the hydrophilic weight percentage of the surfactant by five. For example, a surfactant having a hydrophilic portion weight of 50 has an HLB value of 10. Below is data on the range of HLB values ​​for surfactants.
The HLB value can be estimated from the solubility properties of the surfactant in water and can be used to predict the performance of the surfactant. As a result of experience, the performance of the mixed surfactant is always better than that of a single surfactant.
Table 1 is divided into HLB values ​​by dispersion                     Table 2 is divided into HLB values ​​by application
Not dispersed in water | 1~4 | Â | Water-in-oil emulsion | 4~6 |
Dispersive dispersion | 3~6 | Â | Wettability | 7~9 |
Strongly stirred as a milky dispersion | 6~8 | Â | Oil-in-water emulsion | 8~16 |
Stable emulsion dispersion | 8~10 | Â | Detergent | 13~15 |
Translucent to transparent dispersion | 10~13 | Â | Solubilizers | 10~18 |
In a powdery preparation which can be dispersed in water, the agent is a solid which is insoluble in water and which is finely ground. In order to use them effectively by dilution with water, they must be easily dispersed in water, and the resulting dispersion should be stable for as long as possible. However, since the dispersion containing fine particles is unstable, the particles of the agent tend to be strongly flocculated. Flocculation is caused by van der Waals forces between particles that are close to each other. In order to counteract van der Waals force, a repulsive force is required. The repulsive force is provided by adding a surfactant to the formulation. Two types of repulsive forces, electrostatic attraction and space attraction, act depending on the ionic characteristics of the surfactant. Surfactants can be used to promote the suspension of wettable powder particles in water and also to prevent flocculation of the wettable powder suspension prior to application.
Second, the role of surfactants in emulsifiable concentrates The main role of surfactants in emulsifiable concentrates is to emulsify the original drug present in the non-aqueous medium into the water prior to application of the emulsifiable concentrate. The emulsifiable concentrate is diluted with water to produce an oil-in-water emulsion. . Another aspect of the surfactant in the emulsifiable concentrate is to prevent stratified deposition or flocculation of the emulsion to maintain the formed emulsion in a stable state. The factor causing the destruction of the emulsion is that the liquid film between the droplets becomes thin and the droplet breakage and the bonding between the droplets occur, and the small droplets dissolve and are deposited as large droplets. In practice, the prevention of coalescence can be achieved by the use of a mixed nonionic surfactant, and macromolecular surfactants can also be used to reduce coalescence, which can form membranes that are not spatially interacting, which prevents thinning of the membrane. And destruction. In addition, Austenitic ripening is another cause of emulsion instability. Austenitic ripening is based on the fact that the two liquids are completely immiscible. Thus, molecules between droplets can be transferred from small droplets to large droplets through a continuous phase. This driving force is the difference in solubility between small droplets and large droplets, and the presence of adsorbed surfactants helps to reduce this driving force.
The emulsification of the agent present in the aromatic solvent in water can be achieved by selecting a surfactant having an appropriate HLB value. Mixing the two surfactants often results in the desired HLB value. In emulsifiable concentrates, the most common surfactants are mixtures of anionic surface active and nonionic surfactants. Typically the anionic moiety is based on calcium alkylbenzene sulfonate having an HLB value of about 9.
Third, the role of surface activity in the suspension agent in the suspension processing, surface activity plays an important role as a basic component, they act as an active ingredient to wet the particles before grinding and grinding, they help dissolve The unground premix in the grinding chamber and the stabilization of the fine particles in the dispersion medium (particle size will be less than 40 microns).
When the dry active ingredient is mixed with water during the manufacture of the suspending agent, the surface of each particle should be wetted, and the air between the particles should be discharged. When bubbles are accumulated on adjacent particles, the air remaining on the surface of the particles after grinding causes flocculation and reduces the stability of the dispersion. The most widely used wetting agents are ethoxylated alkyl aryl phenols which have very low foaming properties. Foam formation should always be avoided during the manufacture and application of the suspending agent. Because it can reduce the uniformity of the active ingredients and the effect in the field. The concentration of the wetting agent used is usually from 0.5% to 3%, depending on the concentration, formation and surface properties of the active ingredient.
Surfactants also act as abrasives. The surfactant helps re-wet and disperse the reformed particles during the grinding process. Poor rewetting results in a paste that blocks the pores in the grinding chamber. The wetting and dispersing agents typically have a cloud point greater than 60 ° C (temperature achievable during milling). If the cloud point is low, surfactant desorption from the particles may occur at the cloud point.
Surfactants also contribute to the stability of the formulation. Since the particles of the active ingredient are very fine, the dispersed particles have an inherently irreversible tendency to flocculate as a result of van der Waals forces, and the surfactant can reduce this attraction.
For many years, most commercial preparations have been developed empirically, and the theoretical background that accurately predicts the derivatization properties of surfactants has not yet been well developed. There is no doubt that surfactants can significantly alter the effects of pesticides. It is a future research topic to understand exactly how surfactants work and to use this knowledge to better manufacture pesticide formulations.
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