The water solubility of the long-chain betaine amphoteric surfactant has a temperature-dependent effect. When a 1% aqueous solution is slowly heated, the critical temperature at which the solution suddenly becomes clear from turbidity becomes the Kraff point of the ionic surfactant. The long-chain betaine amphoteric surfactant has not reached the "melting point" of its hydrated solid at room temperature. At this time, the surfactant is in a hydrated solid state, so its water solubility is poor. When the temperature is high enough, the hydrated solid begins to "melt", so the solubility increases significantly. The temperature characteristic of the long-chain betaine amphoteric surfactant is only suitable for use at a temperature higher than the Kraff point to be effective.
Long-chain betaine surfactants, such as erucyl amidopropyl betaine EAB40, cetyl dimethyl betaine BS1618, etc., although they have low solubility in cold water, they dissolve in hot water and are not affected by pH Value.
The longer the hydrophobic chain of the long-chain betaine surfactant, the easier it is to form micelles. As the temperature increases, the hydration of the hydrophilic group of the long-chain betaine surfactant decreases with the increase of temperature, and the ability of the long-chain betaine surfactant to form micelles increases with the increase of temperature.
When customers use long-chain betaine amphoteric surfactants, it is recommended that the aqueous solution is heated to dissolve and used at a temperature higher than the Kraff point.