Amphoteric surfactants are unique molecules that contain both anionic hydrophilic groups (such as carboxyl, sulfonic, or phosphate groups) and cationic hydrophilic groups (such as amino or quaternary ammonium groups) within the same molecule. Their defining characteristic is their ability to both donate and accept protons.

Two Main Types: Amino Acid vs. Betaine

Currently, synthetic amphoteric surfactants are mainly divided into two categories based on the structure of their cationic part:

1. Amino Acid Type

Characteristics: The properties change drastically with the pH of the medium.

• Alkaline Medium: Acts as an anionic surfactant (water-soluble).
• Acidic Medium: Acts as a cationic surfactant (water-soluble).
• Isoelectric Point: Charges balance out, hydrophilicity decreases, leading to precipitation.

Application Note: Must be used at a pH away from the isoelectric point to be effective.

2. Betaine Type

Betaine types are among the most advanced amphoteric surfactants. Their main advantage is solubility in acidic, neutral, or alkaline solutions, with no precipitation even at the isoelectric point.

A. Carboxybetaine

Acts as cationic in acidic media (pH < isoelectric point) and amphoteric in neutral/alkaline media. Compatible with all surfactants except with anionics in strictly acidic conditions.

B. Sulfobetaine

The All-Rounder. Besides standard benefits, it tolerates high concentrations of acid, alkali, and salt. Widely used in oilfield applications. Newer hydroxy-sulfopropyl betaines offer enhanced safety, bactericidal, and antistatic properties.

C. Phosphobetaine

Known for excellent wetting, cleaning, and solubilizing properties. It stands out for its low irritation, strong calcium soap dispersion, low surface tension, and superior foaming abilities.

Summary – Clean Chemical

While amphoteric surfactants may be priced higher than traditional ones, their irreplaceable mildness, compatibility, and stability in harsh environments (high salt, acid/alkali) make them the top choice for premium personal care products and industrial auxiliaries.