Surfactants in Living Systems
The applications of surfactants in living systems are also being widely explored. Anionic surfactant sodium dodecyl sulfate (SDS) is an auxiliary ingredient in gels for separating proteins; research on the use of surfactants as drug carriers, highly polymerized phenolic surfactants as bio-adhesives, environmentally responsive surfactants for the preparation of smart soft materials, and surface-active proteins for assisting in genetic engineering are perfectly blending the ancient surfactants with the “century of living things”. “In recent years, surfactants have been utilized in the production of flexible materials. In recent years, surfactants have also been used in the fields of flexible electronic devices, fuel cells, high-efficiency proton exchange membranes, energy saving and pollution reduction [27]. In addition, some surfactants also have various functions such as sterilization and antistatic. The diversification of surfactant properties has led to a wide range of applications. In addition to daily chemicals, washing, cosmetics, petroleum additives and other fields, surfactants in pesticide emulsions, mineral flotation, textiles and other industries is also very common, and thus has the reputation of “industrial monosodium glutamate”.
It should be noted that sometimes the demand for surfactant properties is diametrically opposed. As far as emulsion is concerned, some systems need to add surfactants to enhance their stability, at this time, surfactants are called emulsifiers; some systems rely on surfactants to break the emulsion, at this time, surfactants are also known as emulsion breakers; in the foam system, surfactants can be used to enhance the foaming performance (foaming agent) can be applied to the defoaming process (defoamer); some surfactants have good biocompatibility, and are used to enhance the foam performance of the foam system (foamer). Some surfactants have good biocompatibility and are used in food, cosmetics and other fields, while some surfactants have strong bactericidal effect and can be realized to be used in antiseptic system. In short, the needs of people’s daily life and industrial and agricultural production are diversified, and should be analyzed on a case-by-case basis when choosing specific surfactants.
At the same time, in addition to the surfactants can play an important role in the case of a single component, different surfactant molecules can produce synergistic effect, resulting in 1 + 1 > 2 effect. Typical examples are anionic/cationic surfactant complex system [28], hydrocarbon/fluorocarbon surfactant complex system, and anionic/nonionic surfactant complex system [30]. In addition, surfactants can also play a more important role together with biomolecules, natural products, synthetic polymers, clays, etc. For example, alveolar surface-active substances play a physiological role by lowering the alveolar tension with the synergistic effect of lipoproteins.
Cationic surfactants
These surfactants are called cationic soaps because they are cationic in nature. The main part of their molecular structure is a pentavalent nitrogen atom, so they are also called quaternary ammonium compounds. It is characterized by large water solubility, more stable in acidic and alkaline solutions, with good surface activity and bactericidal effect. Commonly used varieties include benzalkonium chloride and benzalkonium bromide.
Amphoteric ionic active agent
This kind of surfactant has both positive and negative charge groups in its molecular structure, which can show the properties of cationic or anionic surfactant in different pH media.
1、Lecithin: It is the main excipient for the preparation of emulsion and lipid particle preparation for injection.
2、Amino acid type and betaine type:
Amino acid type: R-NH+2-CH2CH2COO-
Betaine type: R-N+(CH3)2-COO-
It is an anionic surfactant in alkaline aqueous solution with good foaming and decontamination effect; in acidic solution, it is a cationic surfactant with strong bactericidal ability.
Nonionic surfactant
HLB is 3~4, mainly used as auxiliary emulsifier for W/O type emulsion.
Sucrose ester: HLB (5~13) O/W emulsifier, dispersant
Sorbitan fatty acid ester with water loss (Span): W/O emulsifier
Polyoxyethylene sorbitan fatty acid ester (Tween): O/W emulsifier
Resistant to hot-pressure sterilization and low-temperature freezing, emulsifier for intravenous emulsions.
