What are the characteristics and application fields of fluorosurfactants?

2025-04-09 08:47:51

I. Characteristics of Fluorosurfactants

Fluorosurfactants (abbreviated as FS) are surfactants with special properties that have been gradually commercialized in recent years. Different from ordinary surfactants, fluorosurfactants mainly use perfluoroalkyl, perfluoroalkenyl, or partially fluorinated alkyl groups as the hydrophobic part of the surfactant. Then, appropriate linking groups and hydrophilic groups are introduced as needed. According to the nature of the hydrophilic groups, different series of fluorosurfactant products such as anionic, cationic, non-ionic, and amphoteric types are prepared respectively.

Due to the special structure of fluorosurfactants, fluorine atoms replace the hydrogen atoms on the hydrophobic groups of ordinary surfactants, transforming the structure of the C - H bond into the C - F bond form. Therefore, it exhibits some excellent properties unique to fluorocarbons, and at the same time, it has the characteristics of being both hydrophobic and oleophobic. The high surface activity of fluorosurfactants depends on the extremely strong hydrophobicity of the carbon - fluorine bonds in their molecules and the low intermolecular cohesion. It can reduce the surface tension of water to a very low value while using a very small concentration. Generally, the application concentration of hydrocarbon - 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 - 35 dyn/cm (1 dyn = 10⁻³ N/m). When the dosage of fluorocarbon - chain surfactants is between 0.005% and 0.1%, the surface tension of the aqueous solution can be reduced to less than 20 dyn/cm. In addition, fluorosurfactants also show good surface activity in organic solvents. Especially when N - substituted perfluorooctamide is introduced, it can reduce the surface tension of hydrocarbon solvents by 5 - 15 dyn/cm. The excellent thermal stability and chemical inertness exhibited by fluorosurfactants are mainly because after the fluorocarbon - chain hydrophobic group replaces the hydrocarbon - chain hydrophobic group, since the bond energy of the C - F bond (116 kcal/mol) is greater than that of the C - H bond (99.5 kcal/mol), the C - F bond is more stable than the C - H bond and is not easy to break. Also, after fluorine atoms replace hydrogen atoms, due to the larger volume of fluorine atoms than hydrogen atoms, the C - C bond is protected by the shielding effect of fluorine atoms, so that the C - C bond with originally not too high bond energy is also stabilized. Thus, fluorosurfactants have chemical stability and thermal stability that hydrocarbon surfactants do not have. For example, the use temperature of C₉F₁₇OC₆H₄SO₃K can be around 300 °C, and the intermediate C₉H₁₇OC₆H₅ of this compound will not decompose when treated in 50% sulfuric acid or 25% sodium hydroxide aqueous solution at 80 °C for 48 hours.

Research shows that the high surface activity of fluorosurfactants is due to the small van der Waals force between their molecules. The tension required for surfactant molecules to move from the aqueous solution to the solution surface is small, resulting in a large - scale aggregation of surfactant molecules on the solution surface, forming a strong surface adsorption. And such compounds not only have a low affinity for water but also a low affinity for hydrocarbons. Therefore, they form the characteristics of being both hydrophobic and oleophobic. However, its effect on the interfacial tension at the oil/water interface is not strong. If fluorosurfactants are used in combination with hydrocarbon surfactants, fluorosurfactants can be selectively adsorbed on the water surface to reduce the surface tension, while hydrocarbon surfactants can be adsorbed on the oil/water interface to reduce the interfacial tension. This will surely improve the wettability of the aqueous solution.

II. Applications of Fluorosurfactants

Given the characteristics of fluorosurfactants, they have strong applicability in certain fields, especially in the industrial field with various uses. The main applications are as follows:

(1) Dispersibility

Fluorosurfactants can be used as dispersants in the dispersion polymerization of various fluororesins. Fluorosurfactants are used as dispersants in the emulsion - dispersion polymerization of fluorine - containing monomers such as tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride. Their high dispersibility can be utilized in surface treatment agents such as electroplating additives and cleaning agents.

(2) Dehydrating and Release Agents

Fluorosurfactants have good water - repellency, which is very helpful for the surface dehydration treatment of some decorative plating types. Fluorosurfactants can also be used as release agents. They not only have good release properties for thermoplastic polymers but also have excellent release properties for thermosetting polymers and silicone - containing rubber elastomers. And there is no pollution on the demolded workpieces, and secondary processing (such as printing, painting, pasting, etc.) can be carried out directly, and multiple demoldings can be achieved with a single use. Release agents prepared from fluorosurfactants have gradually formed a series of products, including solvent - based and water - based types. It can be used not only in the processing industry of organic polymer elastomers but also in the processing industry of rigid bodies (such as the drawing of copper and steel pipes, pin pressing, stamping of die - castings, etc.). Currently, fluorine - containing (high - efficiency) release agents have been highly praised by users in the processing industries of plastics and rubbers.

(3) Antistatic Agents

The antistatic agent prepared from fluorosurfactants, which combines cleaning and dust - proof functions, has been tested by relevant departments: after surface treatment of PVC film base, its surface resistance is reduced from the original 10¹² Ω to 10⁸ Ω. As a result, the phenomenon of easy dust absorption due to static electricity on the film base surface is greatly reduced. Using this type of antistatic agent to clean the surface of the magnetic drum and magnetic head in a video recorder has a much better effect than ordinary cleaning agents or cleaning tapes and can extend the service life of the magnetic drum and magnetic head. After cleaning the film or phonograph record, the volume can be increased by 3 dB during playback. This type of antistatic agent can also be used for surface cleaning and dust - proofing of household appliances, plastic products, TV screens, and other high - end furniture and precision instruments without side effects.

(4) Leveling Agents

Adding a small amount of surfactants to products such as pigments and coatings can prevent solidification, improve dispersibility. Adding them to coatings and inks can reduce their surface tension, improve wettability, prevent the generation of bubbles, and make the color more uniform.

(5) Other Applications

Adding fluorosurfactants to floor wax can improve the luster of the floor, increase its wear resistance and anti - pollution properties. Fluorosurfactants can also be used as auxiliaries for oil recovery, oil - gathering agents on the sea surface, metal preservatives, and metal luster treatment agents, etc.