What are the characteristics and application fields of fluorinated surfactants?

2025-03-25 15:36:57

I. Characteristics of Fluorinated Surfactants

Fluorinated surfactants (abbreviated as FS) are a special type of surfactant that has gradually become commercialized in recent years. Unlike ordinary surfactants, fluorinated surfactants mainly use perfluoroalkyl or perfluorovinyl groups, or partially fluorinated alkyl groups as the hydrophobic part of the surfactant, and then introduce appropriate linking groups and hydrophilic groups as needed. Depending on the nature of the hydrophilic group, different series of fluorinated surfactant products such as anionic, cationic, nonionic, and amphoteric types can be prepared.

Due to the special structure of fluorinated surfactants, fluorine atoms replace the hydrogen atoms on the hydrophobic group of ordinary surfactants, transforming the structure of C-H bonds into C-F bonds. Therefore, it exhibits some excellent properties unique to fluorocarbons, and it has both hydrophobic and oleophobic characteristics. The high surface activity of fluorinated surfactants depends on the extremely strong hydrophobicity of their molecular carbon-fluorine bonds and the lower internal molecular cohesion. It can reduce the surface tension of water to a very low value, while the concentration used is very small. Generally, the application concentration of carbon-hydrogen chain surfactants needs to be between 0.1% and 1%. At this time, the surface tension of the aqueous solution can only be reduced to 30 to 35dyn/cm (1dyn = 10-3N/m). When the amount of carbon-fluorine bond surfactant is between 0.005% and 0.1%, the surface tension of the aqueous solution can be reduced to below 20dyn/cm. In addition, fluorinated surfactants also show good surface activity in organic solvents, especially after the introduction of N-substituted perfluorooctanamide, which can reduce the surface tension of hydrocarbon acetylene solvents by 5 to 15dyn/cm. The excellent thermal stability and chemical inertness exhibited by fluorinated surfactants are mainly due to the substitution of the hydrophobic group of the carbon-hydrogen chain with the hydrophobic group of the fluorocarbon chain. Since the bond energy of C-F bond (116kcal/mol) is greater than that of C-H bond (99.5kcal/mol), the C-F bond is more stable than the C-H bond and is not easy to break. Also, because the fluorine atom is larger than the hydrogen atom, the C-C bond is protected by the shielding effect of the fluorine atom, so that the originally not very high bond energy of the C-C bond is also stabilized. This makes the fluorinated surfactant have chemical stability and thermal stability that the carbon-hydrogen surfactant does not have. For example: The usage temperature of C9F17OC6H4SO3K can be around 300°C, while the intermediate C9H17OC6H5 is treated at 80°C in 50% sulfuric acid or 25% sodium hydroxide aqueous solution for 48 hours without decomposition.

Studies have shown that the high surface activity of fluorinated surfactants is due to the small van der Waals forces between their molecules. The tension required for the surfactant molecules to move from the aqueous solution to the solution surface is small, resulting in a large accumulation of surfactant molecules on the solution surface, forming a strong surface adsorption. These compounds not only have a small affinity for water, but also have a small affinity for hydrocarbons. Therefore, they form both hydrophobic and oleophobic characteristics, but their effect on the interfacial tension of the oil/water interface is not strong. If fluorinated surfactants are used in combination with hydrocarbon surfactants, fluorinated surfactants can be selectively adsorbed on the surface of water to reduce the surface tension; while hydrocarbon surfactants can be adsorbed on the oil/water interface to reduce the interfacial tension, which will inevitably improve the wettability of the aqueous solution.

II. Application of Fluorinated Surfactants

In view of the characteristics of fluorinated surfactants, they have strong applicability in some fields, especially in the industrial field. Its main applications are as follows:

(1) Dispersibility

Fluorinated surfactants can be used as dispersants during the dispersion polymerization of various fluororesins. Fluorinated surfactants are used as dispersants in the emulsion dispersion polymerization of fluorinated monomers such as tetrafluoroethylene, trifluorochloroethylene, and vinylidene fluoride. In electroplating additives, cleaning agents, and other surface treatment agents, their high dispersibility can be utilized.

(2) Dehydration, release agent

Fluorinated surfactants have good dehydration properties, which is very helpful for the surface dehydration treatment of some decorative plating types. Fluorinated surfactants can also be used as release agents, which not only have good release properties for thermoplastic polymers, but also have excellent release properties for thermosetting polymers and silicone rubber elastomers, and there is no pollution to the workpiece after release, which can be directly subjected to secondary processing (such as printing, painting, pasting, etc.), and can be used multiple times after one use. The release agent prepared from fluorinated surfactants has gradually formed a serialized product, which includes solvent-based and water-based types. It can not only be used in the processing industry of organic polymer elastomers, but also in the processing industry of rigid bodies (such as copper, steel pipe drawing, pressing, die-casting parts stamping processing, etc.). At present, fluorinated (high-efficiency) release agents have been highly praised by users in the plastic, rubber, and other processing industries.

(3) Antistatic agent

The antistatic agent prepared from fluorinated surfactants combines cleaning and dustproof functions. After testing by relevant departments: After the surface of the PVC sheet base is treated, its surface resistance drops from the original 1012Ω to 108Ω. This greatly reduces the phenomenon that the surface of the sheet base is easy to attract dust due to static electricity. Using such antistatic agents to clean the surface of the drum and magnetic head in the video recorder has a much better effect than general cleaners or cleaning tapes, and can extend the service life of the drum and magnetic head. After cleaning, the sound volume of the film or dense record can be increased by 3dB when playing. Using such antistatic agents, household appliances, plastic products, TV screens, and other high-end furniture and precision instruments can also be cleaned and dustproof without side effects.

(4) Leveling agent

After adding a small amount of surfactant to products such as pigments and coatings, it can prevent solidification, improve dispersibility. Adding it to paints and inks can reduce their surface tension, improve wettability, prevent bubble formation, and make the color more uniform.

(5) Other applications

Adding fluorinated surfactants to floor wax can improve the gloss of the floor, increase its wear resistance and anti-pollution properties. Fluorinated surfactants can also be used for oil recovery aids, oil collectors on the sea surface, metal corrosion inhibitors, and metal luster treatment agents.