When anionic surfactants are dissolved in water, they can dissociate negatively charged groups that play a part of the surface activity. It is a product with the longest development history, the largest output and the most varieties among surfactants. Anionic surfactants generally have good penetration, wetting, emulsifying, dispersing, solubilizing, foaming, antistatic and lubricating properties. They have good detergency when used as detergents.
According to the structure of the hydrophilic group, anionic surfactants are mainly divided into four types, carboxylate, sulfonate, sulfate and phosphate. The types of hydrophilic groups of anionic surfactants are limited, while the hydrophobic groups can be composed of various groups, so there are many types.
What Are Performances of Alkyl Sulfates
The general chemical formula of alkyl sulfate is ROS03M, where M can be Na, K, NH4, NH(CH2CH2OH)3, and the number of carbon atoms in R is 8-18. This type of surfactant has good foaming ability and washing performance, is stable in hard water. Meanwhile, iits aqueous solution is neutral or slightly alkaline. So it is mainly used in detergents.
The main representative of alkyl sulfate is sodium lauryl ether sulfate, SLES 70. It is easily soluble in water, has strong foaming power, full, white and fine foam. It also has excellent emulsifying performance and washing ability.
Alkyl sulfate is obtained by sulfating fatty alcohol and neutralizing it with alkali. Industrially, fatty alcohols can be obtained from fats or fatty acid esters through hydrogenation decomposition, or from ethylene through Ziegler reactions. Sulfating agent can use sulfuric acid, chlorosulfonic acid, sulfamic acid, sulfur trioxide etc.
The properties of alkyl sulfate are affected by the chain length and degree of branching of the alkyl group. Experiments have shown that C12-C14 alkyl sulfates have high solubility. C12-C16 alkyl sulfates have a strong ability to reduce surface tension, among which C14-C15 is the strongest. Alkyl sulfates of C12 have the best wettability. C13-C16 alkyl sulfates have excellent washing performance, which is similar to that of α-olefin sulfonates. C14-C15 alkyl sulfates have good foaming properties, which are close to C14-C16 α-olefin sulfonates.
What is the kraff point of ionic surfactant
There is an obvious turning point in the solubility of ionic surfactants with temperature. That is, in a lower temperature range, the temperature rises very slowly. When the temperature rises to a certain value, its solubility increases rapidly as the temperature rises. This temperature is called the Krafft point of the surfactant.
The Krafft point is a characteristic value of ionic surfactants, and it is also the lower limit of the application temperature of surfactants. In other words, only when the temperature is higher than the Krafft point, the surfactant can work better.
For example, the Krafft point of sodium dodecyl sulfate is 8°C, while the Krafft point of sodium dodecyl sulfate is 70°C. When used at room temperature, the former is better as a solubilizer, while the latter has a high Krafft point, which is not ideal.
How Do Anionic Surfactants Work
When the surfactant is dissolved in water, it not only directionally adsorbs on the surface of the solution, but also aligns in the solution to form micelles when the concentration reaches a certain level. There are two possible routes that surfactants can take in order to make themselves stable molecules in solution. One is to leave the hydrophilic group in the water, and the lipophilic group extends to the oil phase or air. The second is to make the lipophilic groups of the surfactant close to each other to reduce the contact area between the lipophilic groups and water. The former is that the surfactant molecules are adsorbed on the interface, and the result is that the interfacial tension is reduced to form an aligned monomolecular film, while the latter forms micelles.
Since the hydrophilic group of the micelles faces outwards and attracts water molecules, the surfactant can be stably dissolved in water. With the increase of surfactant concentration in solution, spherical micelles may transform into rod-shaped micelles and even lamellar micelles. The latter can be used to make liquid crystals, which have anisotropic properties.