Anionic surfactants
Definition: Surfactants with negatively charged parts that play a role in surface activity after ionization in water
Anionic surfactants are classified according to the structure of their hydrophilic groups:
Sulfonates Sulfate salts Carboxylates Phosphate salts
4、Amphoteric surfactants
Definition: molecular structure with both positive and negative charge groups, in different pH media can show the nature of cationic or anionic surfactants.
C. Imidazoline type
By fatty acids and hydroxyethyl ethylenediamine dehydration condensation reaction, first form amide structure, further dehydration to form imidazoline intermediates, and finally react with the corresponding acid, there are two common types:
Excellent foaming and emulsifying properties, mild nature of low toxicity, low irritation, good foaming, emulsifying properties and good biodegradability, can be used in chemical, textile, printing and dyeing baby shampoos and low irritation shampoos, but also used in cosmetics and detergents, softeners of fibers and antistatic agents.
D, Ammonium oxide
Ammonium oxide commonly used alkyl dimethyl amine oxide, alkyl diethanol oxidized amine and alkanoyl propylamine dimethyl amine oxide 3 kinds:
The chemical properties of amine oxide are similar to those of amphoteric surfactants, showing nonionic properties in neutral and alkaline solutions and weak cationic properties in acidic media.
5、Gemini surfactant
Gemini surfactant, consists of two or more identical or nearly identical amphiphilic molecules that are chemically bonded together by a linking group at or near the head group.
Compared with conventional surfactants, Gemini surfactants have high surface activity, low CMC, and their aqueous solutions have special phase behavior and rheology.
There are generally two types, as shown in Figure 1.4, one in which the linking group is directly attached to two hydrophilic groups, and the other in which the linking group is attached to two hydrophobic groups in very close proximity to the hydrophilic groups.
It has a wide range of applications in solubilization, emulsion polymerization, anti-corrosion, detergents, drug dispersants, cosmetics and many other areas.
6、Bola surfactant
Bola-type amphiphilic compounds are amphiphilic compounds consisting of a hydrophobic part connected to two hydrophilic parts. There are three types of Bola-type compounds that have been studied (Figure 1.5) single-chain type, double-chain type and semi-cyclic type. This special structure also gives Bola compounds solutions with unique properties of surface tension, surface adsorption, agglomerates, critical micelle concentration and vesicles.
Bola surfactants have the following properties:
CMC values are generally higher than those of conventional single-head-based surfactants;
Lower critical dissolution temperature in water and higher solubility at room temperature, which can be used as supramolecular aqueous phase gel reagents;
The number of aggregates in the aqueous phase is small, in the form of aggregated micelles such as spheres, rods and disks;
When the hydrophobic chain reaches a certain length, it can form a monolayer lipid membrane (MLM) at the gas-liquid interface, forming ordered molecular aggregates – monolayer vesicles;
The surface activity can be easily changed by changing the two polar heads or hydrophobic chains.
4. Structural Characterization of Surfactants
Products for various applications contain more or less surfactants with different functions. For various mixed samples, it is necessary to separate and purify them by physical separation, chemical separation, silica gel column chromatography, chromatographic separation, etc., and then use spectroscopy, mass spectrometry, chromatography, energy spectroscopy, thermal analysis and other instruments to characterize and quantify the structure of the components contained.
Separation of mixed samples
Step-by-step washing method
Dissolution and precipitation
Chromatographic separation method (column chromatography, thin layer chromatography, HPLC, etc.)
2、The separation principle of chromatography
When the mixture carried in the mobile phase flows through the stationary phase, it interacts with the stationary phase (force action). Since the components of the mixture differ in nature and structure, the magnitude of the interaction with the stationary phase also differs.
Therefore, under the action of a uniform driving force, the retention time of different components in the stationary phase varies from long to short, so that they flow out of the stationary phase in a different order.
Column chromatography separation
3) Elution
Elution system: gradient elution
Volume of eluent: 400-800 parts
Steps: first point plate (TLC) —- plate climbing at 0.3Rf in the drenching system is suitable for washing down the substance.
Note: When passing through the column, the eluent should be used as it is prepared, and the receiving vessel should be changed frequently to avoid crossover.
