What is the Composition of Surfactant

May 20, 2021

Chemically, a surfactant refers to a substance that is amphiphilic (a long strip of solvent that is soluble in the solvent, and the two ends can be separately compatible with each other incompatible solvents), to contain both hydrophilic and lipophilic groups. Groups are the most common;The surfactants on the market are composed of chemical surfactants and their preservation solvents, preservation additives, etc.That is to say, if in a chemical sense, a surfactant refers to a certain kind of substance, it refers to a compound rather than a mixture, so you cannot ask what substance the surfactant is composed of, because surfactant is a concept Rather than specifically refer to a certain substance or a certain mixture.

The type of substance that can be called surfactant is characterized by the different affinities between the two ends of the molecule. Take the most common water and oil surfactants as an example. These surfactants often have an organic carbon chain structure called a hydrophobic group at one end, and a water-soluble group (such as a hydroxyl group) that highlights the polarity at the other end. , Sulfonic acid, carboxylic acid, etc.) are called hydrophilic groups. The most common surfactant in organisms is the phospholipid that composes the cell membrane. The head is a hydrophilic group containing nitrogen and phosphorus, and the tail is a long-chain lipophilic group.

Classification of surfactants There are many types of surfactants, and their performance varies greatly. Its performance depends on the size and structure of the lipophilic group, as well as the type and performance of the hydrophilic group. The influence of hydrophilic groups on the properties of surfactants is far greater than that of lipophilic groups. Therefore, surfactants are generally classified according to the ionization status of hydrophilic groups and the charging properties of their ions. Surfactants are divided into ionic and non-ionic. The former can be ionized in aqueous solution; the latter is not ionized in aqueous solution. Ionic surfactants (including anionic, cationic and zwitterionic surfactants) and non-ionic surface active agents, etc.; some new types of surface active agents.Surfactant molecule is an amphiphilic molecule, which has both lipophilic and hydrophilic amphiphilic properties.The lipophilic group is an atomic group that is easy to dissolve in the oil or be wetted by the oil, and the oil has the property of repelling water for a year. However, the hydrophobic groups are not necessarily all lipophilic groups, and lipophilic groups are only part of the mad water base. Hydrophilic groups are composed of atomic groups that are easily soluble in or wetted by water. The hydrophilic groups of many surfactants are inorganic in nature, but there are also organic substances, such as those of nonionic surfactants.

It is composed of atomic groups that are easily soluble in water or easily wetted by water. Some are inorganic and some are organic, and they all have inorganic properties. There are many polar hydrophilic groups in surfactants commonly used in industry; they mainly include the following categories. (1) Polar hydrophilic groups in anionic surfactantsCarboxylic acid group-COO-; Sulfonate group-SO-3 Sulfate group-OSO-3; Phosphate group-OPO2-3 and so on. (2) Cationic surface activity; the polar hydrophilic group in the agent: primary amino group—NH3·H+; tertiary amino group—(CH3)2N·H+; secondary amino group—CH3NH·H+; quaternary amino group—(CH3)3N+ and so on.(3) Polar hydrophilic groups in amphoteric surfactants: aminocarboxyl-N+H(CH2)2COO-; betaine carboxyl-N+(CH3)2CH2COO- and so on. (4)—Polar hydrophilic groups in non-ionic surfactants—ether groups—O— and hydroxyl—OH in polyethylene glycol type; hydroxyl groups—OH in polyol type. A wide variety of surfactants composed of hydrophilic and lipophilic groups. The small surface of the surfactant is active. The hydrophilicity and water solubility are not only affected by the type of hydrophilic group, but also affected by various conditions. The most important influence on the hydrophilicity of the hydrophilic group is temperature. The water solubility of ionic surfactants increases with increasing temperature. For example, sodium palmitate, which is one of the soaps, is almost insoluble in cold water; the solubility in warm water is also very small, and the solubility increases significantly at about 70°C. The relationship between the water solubility of sodium soap and temperature is shown in Figure . 

It can be seen from the figure that the solubility of sodium soap increases rapidly above the set temperature. This temperature is called the Krafft Point of the corresponding ionic surfactant. Kraff’s characteristic is the temperature at which the solubility of ionic surfactants rises significantly (a narrow temperature range), which is also the temperature at which the concentration of ionic surfactants in water reaches the critical micelle concentration. At this temperature, its solubility is equal to, Critical micelle concentration; sulfonate type and sulfate type anionic surfactants, amine salt type cationic surfactants, plasma type surfactants, most of which can see the Kraff characteristic phenomenon. Contrary to ionic surfactants; the higher the temperature, the more difficult it is to dissolve in water. For example, 10 mol ethylene oxide adduct of nonphenol is dissolved in water and becomes transparent and heated to about 65°C. The solubility of 10 mol ethylene oxide adduct of nonphenol decreases and becomes insoluble in water as the temperature rises. 

As fine "oil droplets" precipitate out, the solution becomes turbid; after a little cooling, the solution becomes clear and transparent again, because 10 mol of nonanol ethylene oxide is added with salty material and soluble water. Nonionic surfactants such as polyethylene glycol type generally have this characteristic, and quickly become insoluble in water above a certain temperature. This temperature is called the cloud point of the surfactant.