1. Water solubility

Because there is a polar bond N→0 in the amine oxide molecule, and the dipole moment is 4.38D, the compound has the characteristics of high polarity and high melting point. It is easily soluble in polar solvents such as water and lower alcohols, but hardly soluble For non-polar solvents such as mineral oil and benzene.

In the aqueous solution, amine oxide exists in a large amount in the form of hydrate (R1R2R3NO·XH2O), but with the change of pH value, the polarity will change. For example, in the alkaline solution with pH>7, it is mainly anionic surfactant. . However, in acidic solutions at pH<3, amine oxides mainly exist in the form of cations [R1R2R3NOH]+. The aqueous solution of amine oxide has weak oxidizing properties, and it is used in cosmetics to make the skin whiter.

2. Surface activity

(1) Surface tension: After adding amine oxide, the surface tension of water will be greatly reduced. For example, the surface tension of pure water is 72.80×10-3N/m. The surface tension at the critical micelle concentration (cmc) of various amine oxides is about 30×10-3N/m. At cmc, the surface tension of amine oxide is much lower than that of quaternary ammonium salt, so the surface activity of amine oxide is better than that of quaternary ammonium salt.

(2) Decontamination: When amine oxide is mixed with AES or AS, it has a synergistic effect on decontamination, but when mixed with LAS, its synergistic effect is not great. The product of washing lipstick uses 12% fatty acid (C12:C18=12:1), 13% non-ionic surfactant, 12% LAS. If a certain amount of amine oxide is added, the cleaning effect will be very good.

(3) Emulsifying power: Emulsifying power is an indicator to measure the quality of emulsifiers. For example, emulsify the amine oxide aqueous solution and petroleum solvent under the same conditions at 70°C, and then observe the volume change after emulsification. The results show that in the amine oxide homologs, the emulsification ability increases with the increase of the carbon number of the long-chain alkyl group. Another feature of amine oxide as an emulsifier is that it can emulsify in a wide range of pH values, especially in acidic media, it can be compatible with quaternary ammonium cations as preservatives and bactericides, not only will not block The anti-corrosion performance of the preservative, and can enhance its anti-corrosion performance, which is beyond the reach of other non-ionic surfactants.

(4) Foaming and foam stabilization: Amine oxide is a highly effective foam stabilizing agent, commonly used in laundry liquids or dishwashing detergents. The product with a dosage of 1% to 5% has mild performance, no irritation to the eyes, and resistance to hard water. It has good performance, and the foam is higher in hard water with pH=9, 300mg/kg. When fatty alcohol sodium sulfate (AS) is mixed with amine oxide, the foam is full and stable, even if there is grease, it will not change. Therefore, it is often used in conjunction with anionic active agents such as LAS, AS, AES, SAS, etc., and has a good anti-irritation effect. The foam produced by amine oxide has a creamy feel and is widely used in shampoos and shower products.

(5) Thickening effect: Amine oxide has a good thickening effect. For example, the mass fraction of amine oxide mixed with AES (1:9) is 15% active substance solution (the following% are all mass fractions), in an acid medium , Even with little salt, the thickening effect is obvious, and it is mild and has good conditioning. Amine oxide 4.5%, AES 8.5%, NaCl 4%, pH=8, viscosity (20°C) up to 7Pa·s, cloud point <-5°C, but for the solubilization and thickening of shampoo, the carbon atom is preferably C14. The thickening effect of amine oxide can also be used in high alkaline bleach (9% C12, 0.5% NaOH, 4% Na2CO3, a small amount of amine oxide), 10% HCl solution added 1.5% dihydroxyethyl tallow base Amine oxide and 1.5% tallow dimethyl ammonium chloride can increase the consistency to 1Pa·S.

When the concentration of amine oxide exceeds a certain range, a very thick middle phase is formed. Even if the temperature is increased, it cannot be changed to an isotropic mobile phase. Therefore, when amine oxide is produced, generally only about 30% aqueous solution can be obtained, which is difficult to obtain For products with higher concentrations, anionic surfactants must be added to obtain higher concentrations of ammonium oxide products.

（4）Compatibility with anionic surfactants

The performance of amine oxide amphoteric surfactants is relatively mild. Anionic surfactants and amine oxides are used in a large number of detergent formulations to reduce the irritation of anionic surfactants and obtain special effects. When the concentration of amine oxide is lower than cmc, mixing with anionic surfactants to form anions and cations will increase the pH of the precipitation, which is caused by the protonation tendency of amine oxide; at cmc, the two form mixed micelles; high At cmc, the formed anion and cation salts are solubilized in the mixed micelles.

When pH≥8, amine oxide shows non-ionic characteristics and can be compounded with anions; when pH≤8, compatibility with anions will produce an immiscible area, resulting in precipitation; when pH≤6, the two are compounded in an appropriate ratio. The amine oxide and anionic surfactant combine to form an anion-cation pair to form a transparent solution. At this time, the anion-cation salt is solubilized in the excess surfactant micelles. If dimethyl amine oxide is used instead of dimethyl amine oxide, the compatibility will be better; if it is replaced by amine oxide containing polyoxyethylene ether segments, the effect will be the best.

(5) Physiological toxicity

Amine oxide is a non-toxic or low-toxic substance. The commercial stock solution has primary irritation to the skin of rabbits, and the eyes are moderately irritating. At 2% concentration, there is no irritation; it has been fed and coated with alkyl dimethyl for two years. Amine oxide, no carcinogenesis caused by amine oxide has been found. The biodegradability of amine oxide is good, 88% can be degraded after 2 weeks and 93% in 4 weeks. Amine oxide is basically non-toxic and has very low irritation to the skin and eyes. According to KLein report: The LD50 of amine oxide is 2000mg/kg～6000mg/kg, which is almost equivalent to the LD50 of table salt of 4000mg/kg. When mixed with other active agents, amine oxide has anti-irritation properties and can be used in anti-dandruff shampoos to reduce the irritation of ZPT. In addition, in acidic shampoos and acidic solutions, amine oxide can interact with the carboxyl groups on the hair and skin angles. It can condition the hair, reduce flutter, easy to wet comb, and improve the roughness of the skin.

(6) Antimicrobial

Alkyl amine oxide has a certain antibacterial activity, but it does not reach the strong bactericidal properties of quaternary ammonium salt. However, formula products containing amine oxide have their own antiseptic properties, which can prevent the growth of mold and maintain high activity in very dilute solutions. . Some compound amine oxides even show higher bactericidal properties, and are used in soaps as bactericidal deodorants, and even iodine-containing bactericides are formulated to increase the solubility and stability of iodine, and play a role in sterilization and synergy. Among them, the effect of dodecyl dimethyl amine oxide on inhibiting the growth of Staphylococcus aureus is equivalent to that of the corresponding cationic surfactant, while the sterilization effect of other amine oxides is relatively poor.

(7) Antistatic

Amine oxide has high hygroscopicity and ionization tendency, and can form a conductive continuous film on the surface of fiber or resin, so it has excellent antistatic properties. Compared with other antistatic agents, its biggest feature is the change with environmental humidity , The antistatic effect has little change, and it shows good antistatic performance even under lower humidity. Amine oxide also has certain thermal stability and good lubricity, can be compatible with common lubricants, emulsifiers and other antistatic agents, and is easy to use.

(8) Antioxidant

Amine oxide not only can stably exist in hypochlorite solution by itself, but also helps other surfactants stabilize hypochlorite, so it is widely used in sterilization and disinfection detergents.