As the name suggests, zwitterionic surfactants are surfactants that have both anionic and cationic hydrophilic groups. When used alone, zwitterionic surfactants have insufficient washing, emulsifying, and wetting abilities, and are rarely used for wetting and emulsifying. However, when formulated with anionic or cationic surfactants, they exhibit strong cleaning and foam-enhancing effects. In addition, their excellent rheological properties, water solubility, calcium soap dispersibility, and good biodegradability can compensate for their disadvantages, making them increasingly valued in cosmetics.
Zwitterionic imidazolines are tertiary amine compounds with 2-alkyl hydroxyethyl imidazoline as a side chain, which is synthesized by the condensation reaction of long-chain fatty acids and ethanolamine, followed by alkylation reaction to generate zwitterionic imidazolines. Due to the different types and amounts of alkylating agents, a series of zwitterionic imidazolines can be generated. However, cyclic imidazoline derivatives are prone to ring-opening hydrolysis, forming acyl zwitterionic acid or its salt compounds. Zwitterionic imidazolines undergo hydrolysis under strong acid or alkali conditions, but they are stable under cosmetic use.
In addition, acyl zwitterionic acid and its salt compounds are mild zwitterionic surfactants, which can be compounded with all types of surfactants, with high tolerance to hard water. Complexing with anionic surfactants can reduce their irritation to the eyes, without affecting their foaming effect. They are commonly used in mild shampoos and bath products, and shampoos containing zwitterionic imidazolines can make hair soft, easy to comb and anti-static, with a pH range of 6.5-7.5.
This type of molecule is an amino acid derivative produced by the reaction of chloroacetic acid or acrylic acid with alkylamine. N-alkyl amino acid propionic acid is insoluble in water, but its sodium salt is soluble in water, and exists in a zwitterionic form in acidic or alkaline media, which is stable under cosmetic use.
N-alkyl amino acids can be compounded with other surfactants, electrolytes, and hard water ions. They are also stable to oxidants, hydrolysis, and acid-base conditions. They are good emulsifiers, wetting agents, and detergents in alkaline conditions. They are good foaming agents in neutral to alkaline conditions, but lose their foaming properties in acidic conditions. Importantly, they have low irritation and can reduce the irritation of other surfactants to the eyes.
Betaine-type amphoteric surfactants were first obtained from betaine, and are industrially prepared by the reaction of alkyl dimethyl tertiary amine with halogenated acetic acid salt. If the alkyl dimethyl tertiary amine is dodecyl dimethyl tertiary amine, the product obtained after the reaction is dodecyl dimethyl betaine, which is easily soluble in water, forming a transparent solution with good foaming and washing abilities, and is stable to hard water.
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