The basic properties of surfactants
1. Critical micelle concentration (CMC): The minimum concentration at which surfactant molecules associate to form micelles. When its concentration is higher than the CMC value, the arrangement of surfactants is spherical, rod-like, bundle-like, layered/plate-like and other structures.
2. Hydrophilic-lipophilic balance (HLB): The comprehensive affinity of hydrophilic and lipophilic groups in surfactant molecules to oil or water. According to experience, the HLB value range of surfactant is limited to 0-40, and the HLB value of non-ionic type is 0-20.
Mixed additivity: HLB=(HLBa Wa+HLBb /Wb) / (Wa+Wb)
Theoretical calculation: HLB=∑（HLB value of hydrophilic group）+∑（HLB of lipophilic group）-7
The basic properties of surfactants
3. Solubilization
1) Micellar solubilization: The solubility of water-insoluble and slightly soluble drugs increases significantly in micellar solution
Felodipine-----0.025% Tween-----10 times
(Table) Hydrophilic group---lipophilic group,
(Drug) polar group---nonpolar group
?cmc, "table" amount?, micelle?, solubilizing amount?, maximum solubilizing concentration (MAC)
APPLICATION OF SURFACTANTS
1. Solubilization: C>CMC (HLB13~18)
The solubilizing system is a thermodynamic equilibrium system
The lower the CMC and the larger the association number, the higher the solubilization capacity (MAC)
Influence of temperature on solubilization: temperature affects the formation of micelles, the dissolution of solubilizers, and the solubility of surfactants
Krafft point: The solubility of ionic surfactant increases sharply with the increase of temperature. This temperature is called Krafft point. The higher the Krafft point, the smaller the critical micelle concentration.
Depression point: For polyoxyethylene type nonionic surfactants, when the temperature rises to a certain level, the solubility drops sharply and precipitates, and the solution appears turbid. When the polyoxyethylene chain is the same, the longer the hydrocarbon chain, the lower the cloud point; when the hydrocarbon chain is the same, the longer the polyoxyethylene chain, the higher the cloud point.
2. Emulsification:
HLB: 3-8 W /O type emulsifier: Tween; monovalent soap
HLB: 8-16 O/W type emulsifier: Span; divalent soap
3. Wetting: (HLB: 7-9)
4. Suspension:
5. Shooting and defoaming
6. Disinfection and sterilization
7. Detergent
The structure of surfactant
Traditionally, surfactants are a class of substances that can significantly reduce surface (interfacial) tension even at very low concentrations. With the in-depth study of surfactants, it is generally believed that as long as the surface (interface) properties or the properties derived from them can be significantly changed at lower concentrations, they can be classified into the category of surfactants. .
No matter what kind of surfactant, its molecular structure consists of two parts. One end of the molecule is a non-polar lipophilic hydrophobic group, sometimes called a lipophilic group; the other end of the molecule is a polar hydrophilic hydrophilic group, sometimes also called an oleophobic group or vividly called a hydrophilic head. Two types of molecular fragments or groups with diametrically opposed structures and properties are located at both ends of the same molecule and are connected by chemical bonds, forming an asymmetric and polar structure, thus endowing this type of special molecule with both hydrophilic and And lipophilic, it is not the overall hydrophilic or lipophilic properties. This unique structure of surfactants is usually called "amphiphilic structure" (amphiphilic
structure), surfactant molecules are therefore often referred to as "amphiphilic molecules".
Depending on the required properties and specific applications, sometimes surfactants are required to have different hydrophilic and lipophilic structures and relative densities. The desired balance of hydrophilic and lipophilic can be achieved by changing the types, proportions and positions of hydrophilic or lipophilic groups in the molecular structure. After years of research and production, many types of surfactants have been derived, and each type contains many varieties, which brings difficulties to identifying and selecting a specific variety. Therefore, it is necessary to make a scientific classification of thousands of surfactants, which is conducive to further research and production of new varieties, and provides convenience for screening and application of surfactants.
The historical development of surfactants
The formation of an industry of surfactants and synthetic detergents can be traced back to the 1930s. Synthetic surfactants and detergents derived from petrochemical raw materials broke the situation of soap domination. After more than 60 years of development, in 1995, the total output of detergents in the world reached 43 million tons, including 9 million tons of soap. Experts predict that the world's population will double from 2000 to 2050, and the total amount of detergent will increase from 50 million tons to 120 million tons, with a net increase of 1.4 liters, which is an encouraging figure.
China's surfactant and synthetic detergent industry started in the 1950s. Although it started late, it has developed rapidly. In 1995, the total amount of cleaning products reached 3.1 million tons, ranking second in the world after the United States. Among them, the production of synthetic detergents increased 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%. According to the forecast of authoritative departments in China, 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 varieties of surfactants with an output of more than 10,000 tons include: sodium linear alkyl benzene sulfonate (LAS), sodium fatty alcohol polyoxyethylene ether sulfate (AES), fatty alcohol polyoxyethylene ether ammonium sulfate (AESA), lauryl Sodium alcohol sulfate (K12 or SDS), nonylphenol polyoxyethylene (10) ether (TX-10), peregalo O, diethanolamide (6501) stearic acid monoglyceride, lignosulfonate, heavy alkane Base benzene sulfonate, alkyl sulfonate (petroleum sulfonate), diffusing agent NNO, diffusing agent MF, alkyl polyether (PO-EO copolymer), fatty alcohol polyoxyethylene (3) ether (AEO- 3) etc.
The relationship between the chemical structure and properties of surfactants
1. The relationship between the balance between the affinity and the performance
H·L·B value: Indicates the hydrophilic and hydrophobic properties of surfactants
(Hydrophile-Lipophile Balance)
Surfactant should present a unique boundary