An in-depth look at surfactants

An in-depth look at surfactants
A surfactant is a substance that significantly reduces the surface tension of a target solution. It has fixed hydrophilic and lipophilic groups that are oriented on the surface of the solution. The molecular structure of surfactant is amphoteric: hydrophilic group at one end, hydrophobic group at the other end; hydrophilic groups are often polar groups, such as carboxylic acid, sulfonic acid, sulfuric acid, amino or amine groups and their salts, hydroxyl, amide, ether bonds, etc., can be used as polar hydrophilic groups; and hydrophobic groups are often nonpolar hydrocarbon chains, such as more than 8 carbon atoms hydrocarbon chain. Surfactants are divided into ionic surfactants (including cationic surfactants and anionic surfactants), nonionic surfactants, amphoteric surfactants, complex surfactants, and other surfactants.

Introduction
Surfactant is a substance that can make the interfacial state of the solution system change significantly by adding a small amount of it. It has fixed hydrophilic and lipophilic groups, which can be arranged directionally on the surface of the solution. The molecular structure of surfactant has amphiphilic: one end is hydrophilic group, the other end is hydrophobic group; hydrophilic groups are often polar groups, such as carboxylic acid, sulfonic acid, sulfuric acid, amino or amine groups and their salts, hydroxyl, amide, ether bonds, etc. can also be used as polar hydrophilic groups; and hydrophobic groups are often nonpolar hydrocarbon chains, such as more than 8 carbon atoms hydrocarbon chain. Surfactants are divided into ionic surfactants (including cationic surfactants and anionic surfactants), nonionic surfactants, amphoteric surfactants, complex surfactants, and other surfactants.
History of origin
(1) 2500 B.C.E. – 1850 Sheep’s Oil and Grass Ash for Soap Manufacturing
Goat oil – tricarboxylic acid ester referred to as triglyceride, hydrolyzed by alkali → carboxylate + monoglyceride + diglyceride + glycerol
In the middle of the 19th century
On the one hand, soap began to achieve industrialized mass production, on the other hand, there is also the emergence of chemically synthesized surfactants.
②The appearance of Turkish red oil:
Turkey red oil that castor oil and sulfuric acid reaction products, castor oil for ricinoleic acid triglyceride, deeply sulfonated, acid and hard water resistant
(iii) In the early 19th century, detergents were prepared from mineral raw materials.
The development of the petroleum industry → petroleum sulfuric acid (green oil). Sulfonated mixture of wax and tea, dissolved in acid, greenish-black, neutralized with alkali to produce. Petroleum sulfonic soap has good water solubility and is called sodium green (first detergent made from mineral raw materials). During World War I, grease appeared, coal production → coal chemical industry developed → short-chain alkyl, nesulfonate surfactants, such as propyl nesulfonate, butyl nesulfonate+

1920-1930 fatty alcohol sulfation → alkyl sulfates. 1930s, long chain alkyl, phenyl appeared in the United States. After World War I, Germany developed ethylene glycol derivatives, such as polyethylene glycol Derivatives of products, polyethylene glycol and a variety of organic compounds (including alcohols, acids, esters, amines, amides), such as the combination of a variety of excellent performance of nonionic surfactants.
Surfactants and synthetic detergents to form an industry can be traced back to the 1930s, to petrochemical raw materials derived from synthetic surfactants and detergents to break the dominant situation of soap. After more than 60 years of development, in 1995 the world’s total output of detergents reached 43 million tons, of which 9 million tons of soap. According to experts’ prediction, the world’s population will double from 2000 to 2050, and the total amount of detergents will increase from 50 million tons to 120 million tons, a net increase of 1.4 times, which is an encouraging figure.
China’s surfactant and synthetic detergent industry began in the 1950s, and although it started late, it has developed rapidly. in 1995, the total amount of detergents had reached 3.1 million tons, second only to the United States, ranking second in the world. The production of synthetic detergents rose from 400,000 tons in 1980 to 2.3 million tons in 1995, a net increase of 4.7 times, and an average annual growth rate of more than 10% of the rate of growth. According to the forecast of Chinese authorities, the total amount of detergents will reach 3.6 million tons in 2000, of which synthetic detergents will reach 655,000 tons. Among them, the surfactant varieties with an output of more than 10,000 tons include: sodium straight-chain alkylbenzene sulfonate (LAS), sodium aliphatic alcohol polyoxyethylene ether sulfate (AES), ammonium aliphatic alcohol polyoxyethylene ether sulfate (AESA), sodium lauryl sulfate (SDS), lauryl glutamate, nonylphenol polyoxyethylene ether (TX-10), ping pinga O, mono ester of stearic acid glyceryl ester, lignin sulfonate, heavy alkylbenzene sulfonate, Alkyl sulfonates (petroleum sulfonates), Diffuser NNO, Diffuser MF, Alkyl polyethers (PO-EO copolymers), Fatty alcohol ethoxylates (AEO-3), etc.
Definition

Definition
Any substance that can significantly reduce the surface energy of water when dissolved in water is called a surface active agent (SAA) or surface active substance.
Traditionally, surfactants have been considered to be a class of substances that can significantly reduce surface (boundary) tension even at very low concentrations. With the deepening of the research on surfactants, it is generally believed that any substance that can significantly change the surface (boundary) properties or the properties related to or derived from them at a low concentration can be categorized as a surfactant.
Surfactants are natural, such as phospholipids, choline, proteins, etc., but more synthetic, such as sodium octadecyl sulfate C18H37SO4Na, sodium stearate C17H35COONa, etc. . The range of surfactants is very broad (cationic, anionic, nonionic and amphoteric), providing a variety of functions for specific applications, including foaming effect, surface modification, cleansing, emulsions, rheology, environmental and health protection.
Chemical structure
Amphiphilic Molecules
Surfactant molecules are uniquely amphiphilic: hydrophilic polar groups at one end, referred to as hydrophilic groups, also known as oleophobic or oleophobic groups, sometimes figuratively referred to as hydrophilic heads, e.g., -OH, -COOH, -SO3H, -NH2; and lipophilic nonpolar groups, referred to as lipophilic groups, also known as oleophobic or oleophobic groups, e.g., R-(alkyl), Ar-(aryl), at the other end. Two types of molecular fragments or groups with diametrically opposed structures and properties are located at the two ends of the same molecule and are chemically bonded, forming an asymmetric, polar structure, which gives the special molecules both hydrophilic and lipophilic, but not the overall hydrophilic or lipophilic properties. This unique structure of surfactants is often called “amphiphilic structure” (amphiphilic structure), and surfactant molecules are often called “amphiphilic molecules”.
Surfactants
For convenience, the surfactant molecule is often represented by a symbolic rectangle with a circle, as shown in the figure above. The rectangle represents the lipophilic group and the circle represents the hydrophilic group.
H-L-B Value
For a surfactant to exhibit characteristic interfacial activity, there must be a certain balance between hydrophobic and hydrophilic groups. The Hydrophile-Lipophile Balance, or HLB value, indicates the hydrophilic and hydrophobic properties of a surfactant, e.g., paraffin HLB value = 0 (no hydrophilic groups) polyethylene glycol HLB value = 20 (completely hydrophilic). For anionic surfactants, the HLB value can be determined by emulsifying the standard oil, and the HLB value can be used as a reference basis for selecting surfactants.
Turbidity point
For nonionic surfactants, hydrophilicity depends on the number of ether bonds, and the combination of ether and water molecules is an exothermic reaction.
When the temperature rises, the water molecules gradually detach from the ether bond, and the phenomenon of turbidity occurs, just when the temperature of turbidity is called the cloudy point. At this point the surfactant loses its effect. The higher the cloud point, the wider the temperature range of use.
Properties
Surfactants reduce the surface tension of water by adsorption at the gas-liquid interface, and can also reduce the interfacial tension of oil and water by adsorption between liquid interfaces. Many surfactants can also aggregate into aggregates in native solutions.
Vesicles and micelles are such aggregates. The concentration at which surfactants begin to form micelles is called the critical micelle concentration or CMC.When micelles form in water, the tails of the micelles form nuclei capable of wrapping around the oil droplets, while their (ionic/polar) heads are capable of forming an outer shell that remains in contact with the water. Surfactants aggregate in oil and the aggregates refer to antimicelles. In anticlusters, the head is in the nucleus and the tail maintains full contact with the oil. Surfactants are usually classified into four major groups: anionic, cationic, nonionic, and amphoteric (two-electron). The thermodynamics of surfactant systems is important, both theoretically and practically. This is because surfactant systems represent systems that are intermediate between ordered and disordered states of matter. Surfactant solutions may contain ordered phases (micelles) and disordered phases (free surfactant molecules and/or ions). Micelles – The lipophilic tails of surfactant molecules are clustered inside the micelles to avoid contact with polar water molecules; the polar hydrophilic heads of the molecules are exposed on the outside, interacting with polar water molecules and protecting the hydrophobic groups inside the micelles. The compounds that form micelles are generally amphiphilic molecules, so generally the micelles are soluble in polar solvents such as water, but also in the form of antimicellular micelles soluble in non-polar solvents.