The emergence of surfactants has transformed people's lives, with applications permeating almost every field, becoming formulations indispensable in modern industry and daily life. Due to the unique properties of cationic surfactants, their applications are increasingly widespread. Several special forms of cationic surfactants have become extraordinary, serving as secret weapons in the development of products with special functions and can be considered as the "hidden weapons" in the development of special new products. Currently, several types of specialized cationic surfactants that are actively researched include:
Cationic surfactants capable of co-solubilizing with anions without generating precipitation, while also exhibiting strong synergistic enhancing effects. Examples include polyoxyethylene alkyl quaternary ammonium salts, polyoxyethylene succinic acid monoesters quaternary ammonium salts, and polyoxyethylene dehydrated sorbitol mono-fatty acid ester quaternary ammonium salts.
Gemini cationic surfactants with low oligomerization or polygeneration. Examples include long-chain alkyl Gemini quaternary ammonium salts, long-chain alkyl trimeric quaternary ammonium salts, double long-chain alkyl quaternary ammonium salts, and polyoxyethylene alkyl Gemini and trimeric quaternary ammonium salts. These surfactants exhibit higher surface activity, lower critical micelle concentration, and excellent compatibility enhancing performance.
Naturally non-toxic and biodegradable cationic surfactants. Examples include alkyl glucoside quaternary ammonium salts, sucrose mono-fatty acid ester quaternary ammonium salts, rosin ester quaternary ammonium salts, cellulose ether quaternary ammonium salts, starch ether quaternary ammonium salts, guar gum ether quaternary ammonium salts, and amino acid ester quaternary ammonium salts. These cationic surfactants have natural sources, extremely low toxicity, and belong to green surfactants. Additionally, due to the weak ether and ester bonds, they easily decompose in the natural environment, contributing to strong environmental protection efficacy. This addresses the contradiction between societal development needs and the deteriorating natural environment.
Polymer cationic surfactants, aside from natural cationic polymers, can be synthesized by adding hydrophobic and hydrophilic groups as needed. Examples include styrene-acrylic acid cationic surfactants and polyacrylamide cationic surfactants, each possessing various special effects.
Cationic surfactants with non-complete carbon atoms, such as silicon-containing cationic surfactants and fluorine-containing cationic surfactants. Due to the unique properties of these special cationic surfactants, they can be used in the design and manufacture of industrial and civil products with special effects. They find applications in fields such as detergents, germicides, personal care products, textile printing and dyeing auxiliaries, papermaking auxiliaries, oilfield auxiliaries, polymer materials, catalytic synthesis, nanomaterials, water treatment, metal processing and protection, construction auxiliaries, and transportation auxiliaries. These applications lead to the development of many new products with superior efficacy, lower costs, and outstanding performance.
Polyoxyethylene-Based Cationic Surfactants: This category of surfactants includes fatty alcohol polyoxyethylene ether monoquaternary ammonium salts, fatty alcohol polyoxyethylene ether quaternary ammonium salts, and dehydrated sorbitol mono-fatty acid ester polyoxyethylene ether quaternary ammonium salts. The molecular structure of these products contains ethylene oxide (EO) groups, reducing the charge density of surfactant ions. This reduction weakens the electrostatic interaction between anions and cations, increases the hydrophilicity of anion-cation complexes, allowing cationic and anionic surfactants to co-solubilize without forming precipitates. Contrary to the common belief that cationic and anionic surfactants cannot be co-solubilized, especially in equimolar mixing, the addition of quaternary ammonium salts with ethoxy groups can address this issue. As long as there are sufficient EO groups, these surfactants can almost co-solubilize and co-formulate with all anionic surfactants. The addition of these special cationic surfactants to anionic surfactant systems results in several noticeable changes in performance:
Reduction in surface tension: Adding a small amount of cationic surfactant significantly lowers the surface tension of the system.
Significant reduction in critical micelle concentration (cmc), with an efficiency increase of up to 10,000 times, leading to strong synergistic effects.
Marked enhancement effect: Addition of cationic surfactants improves cleaning power, extends foam "life," increases viscosity, enhances stability, improves wetting, reduces surface contact angle, significantly boosts emulsification, and reduces the amount of emulsifier required. Gemini cationic surfactants, especially those with good antistatic, antibacterial, and antifungal properties, can be utilized to develop patented products with various new functionalities, such as 2-in-1 shampoo and conditioner or dual-purpose dishwashing detergent. These cationic surfactants can be easily incorporated into anionic systems without the need for "encapsulation" technology, making them convenient in formulation design and product manufacturing. However, due to the relatively complex preparation process and challenging control, there are still relatively few industrialized products in China, while they are widely used in foreign special-effect products, such as "dust-resistant soft laundry powder."
Gemini Cationic Surfactants: Gemini cationic surfactants are a type of surfactant with two hydrophilic (or more) and two hydrophobic (or more) groups within a single molecule. Compared to traditional surfactants, Gemini surfactants have the following properties:
Higher adsorption at the interface between two phases, with adsorption capacities 10 to 10,000 times higher than traditional surfactants. This makes them highly efficient in reducing surface tension, foaming, stabilizing foam, and emulsification.
Lower critical micelle concentration (cmc), only 1/10 to 1/100 of traditional surfactants, indicating lower irritation, superlative solubilization effects, and cost advantages.
More closely packed micelle structures and double the charge heads, leading to stronger synergistic effects when combined with other surfactants. Particularly, when combined with anionic surfactants, especially those with EO groups, the synergistic effects become more pronounced.
Due to the doubled charge, they are less sensitive to electrolytes, exhibiting excellent compatibility.
These cationic surfactants possess stronger bactericidal capabilities than single-chain cationic surfactants.
They exhibit stronger phase-transfer catalysis capabilities (much better than CTAB).
Because of their special properties, such as stable vesicles that can last for several months, Gemini cationic surfactants can be used as excellent wetting agents, foam boosters, foam stabilizers, thickeners, potent bactericides (with killing power 100 times that of benzalkonium chloride), emulsion emulsifiers, and synergistic enhancers.
Ester Quaternary Ammonium Salt Cationic Surfactants: Ester quaternary ammonium salts are considered the second significant transformation in surfactant history after the direct chain ABS replaced branched chain ABS. These surfactants are widely used in fabric softeners, paper softeners, hair care products, and other industrial auxiliary fields due to their outstanding biodegradability and extremely low toxicity to aquatic organisms. They have partially or completely replaced stable yet non-biodegradable alkyl quaternary ammonium salts abroad. These surfactants are particularly stable under acidic conditions and exhibit instability under alkaline conditions. For example, converting polyoxyethylene ether surfactants into ester quaternary ammonium salt surfactants not only combines the advantages of non-ionic and cationic surfactants but also allows co-solubilization and co-formulation with anionic surfactants. This significantly expands the application scope of environmentally friendly surfactants, making them the preferred choice for new product and formula development.
Utilizing the unique properties of special surfactants to research and develop new functional products has become a development hotspot in the domestic industry. Surfactant manufacturing enterprises must continuously produce novel surfactants to provide the "rice" for downstream enterprises. Moreover, the application of new surfactants by end-users will undoubtedly drive the development of novel and specialized surfactants.