The role of surfactants! !
Surfactants have become a class of flexible due to a series of physicochemical effects such as wetting or anti-sticking, emulsification or demulsification, foaming or defoaming, and solubilization, dispersion, washing, antisepsis, antistatic, and corresponding practical applications. , Wide range of fine chemical products. In addition to surfactants as detergents in daily life, other applications can cover almost all fine chemical fields.
Solubilization
Requirements: C>CMC (HLB13~18) Critical micelle concentration (CMC): The lowest concentration of surfactant molecules associated with micelle formation. When the concentration is higher than the CMC value, the surfactants are arranged in a spherical, rod-like, bundle-like, lamellar/planar structure. The solubilization system is a thermodynamic equilibrium system; the lower the CMC and the greater the number of associations, the higher the solubilization amount (MAC); the effect of temperature on solubilization: temperature affects the formation of micelles, affects the dissolution of solutes, and affects the surface The solubility of the active agent Krafft point: The solubility of the ionic surfactant increases sharply with increasing temperature. This temperature is called the Krafft point. The higher the Krafft point, the smaller the critical micelle concentration is. Ionic surfactants, when the temperature rises to a certain degree, the solubility drops sharply and precipitates out, and the solution appears cloudy. This phenomenon is known as cockroaches. This temperature is called the defect point. When the polyoxyethylene chain is the same, the longer the hydrocarbon chain, the lower the cloud point; when the carbon chain is the same, the longer the polyoxyethylene chain, the higher the cloud point.
2. Emulsification
Hydrophile-Lipophile Balance (HLB): The combined affinity of hydrophilic and lipophilic groups in oils or water in surfactant molecules. As a rule of thumb, the HLB range of surfactants is limited to 0-40, and the nonionic HLB is 0-20. Mixed additive: HLB = (HLBa Wa + HLBb / Wb) / (Wa + Wb) Theoretical calculations: HLB = ∑ (hydrophilic group HLB value) + ∑ (oleophilic group HLB) - 7 HLB: 3- 8 W/O emulsifier: Span; divalent soap HLB: 8-16 O/W emulsifier: Tween; monovalent soap
3. Wetting effect
Requirements: HLB: 7-9. The use of surfactants can control the degree of wetting between liquids and solids. In the pesticide industry, granules and powders for dusting powders also contain a certain amount of surfactants. Their purpose is to increase the adhesion and deposition of the drug on the surface of the drug, and to increase the active ingredient in the presence of moisture. The speed of release and the area under it will increase the effectiveness of disease prevention and treatment. In the cosmetics industry, acting as an emulsifier is an indispensable ingredient in skin care products such as creams, lotions, cleansers, and makeup removers.
4. Suspension effect
In the pesticide industry, WPs, ECs, and emulsions all require a certain amount of surfactant. For example, in wettable powders, the original drugs are mostly organic compounds that are hydrophobic, and only in the presence of surfactants, the water-reducing surface Tension, drug particles may be wetted by water to form an aqueous suspension;
5. Foaming and defoaming
Surfactants are also widely used in the pharmaceutical industry. In pharmaceuticals, some volatile oil-soluble celluloses, steroid hormones, and many other insoluble drugs make use of the solubilizing effect of surfactants to form transparent solutions and increase the concentration; during the preparation of pharmaceuticals, it is an indispensable emulsifier and wetting agent. Agents, suspending agents, foaming agents and defoamers.
6. Sterilization, sterilization
In the pharmaceutical industry, they can be used as fungicides and disinfectants. Their bactericidal and disinfecting effects can be attributed to their strong interaction with bacterial biofilm proteins that cause them to denature or lose their function. These disinfectants have relatively large solubility in water. The use of concentration can be used for preoperative skin disinfection, wound or mucosal disinfection, device disinfection and environmental disinfection;
7. Hard water resistance
Betaine surfactants exhibit very good stability to calcium and magnesium ions, ie, their ability to withstand calcium and magnesium hard ions and dispersion of calcium soap. Prevent the precipitation of calcium soap during use and improve the use effect.
8. Thickening and foaming
Surfactants have the effect of changing the solution system, increasing the viscosity to thicken or increase the system's foam, and are widely used in some special cleaning and mining industries.
9. Detergency and washing
Removing greasy dirt is a complex process that is related to the above-mentioned effects of wetting and blistering. The last thing to note is that surfactants work, not just because of a certain role, but in many cases it is a combination of factors. Such as in the paper industry can be used as cooking agent, waste paper deinking agent, sizing agent, resin barrier control agent, defoamer, softener, antistatic agent, scale inhibitor, softener, degreasing agent, sterilization Algae agents, corrosion inhibitors, etc.
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