Surfactants belong to amphiphilic compounds, which means that their molecules include a long hydrophobic group and a hydrophilic group. The hydrophilic group tends to dissolve in water, but is hindered by the hydrophobic group, which tends to dissolve in oil or leave the aqueous phase. As a result, the entire molecule spontaneously adsorbs to the water/air interface and the oil/water interface, forming an oriented monolayer where the hydrophilic and hydrophobic groups each go to their respective locations, resulting in the lowest free energy. The oriented adsorption of surfactants at interfaces causes a decrease in the surface tension of water, hence surfactants are referred to as having surface activity.
From a molecular structure perspective, non-ionic surfactants are also composed of a hydrophilic portion and a hydrophobic portion. The hydrophobic portion is mainly composed of a hydrocarbon chain derived from natural fats and petrochemical raw materials, while the hydrophilic portion mainly consists of polyoxyethylene groups and polyols (hydroxy groups), as well as amides and amines. The hydrophobic raw materials used to prepare non-ionic surfactants mainly include fatty alcohols (including natural and synthetic alcohols), alkylphenols, fatty acids, fatty amines, and epichlorohydrin; while the hydrophilic raw materials are epoxides, polyols, glucose, etc.
Therefore, according to the hydrophilic group classification method, non-ionic surfactants include polyoxyethylene type, polyol fatty acid ester type, alkyl glucoside type, alkylamide type, polyether type, and amine oxide type, among others. Polyoxyethylene-type non-ionic surfactants can be classified into long-chain fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene alkyl amine, polyoxyethylene alkylamide, and polyether, according to the type of hydrophobic group.
Non-ionic surfactants cannot dissociate into ions in aqueous solutions and exist in a neutral molecular state, making them highly chemically stable and not easily affected by acids, bases, and salts in the aqueous phase. Non-ionic surfactants are mostly in liquid or paste form and their solubility in water decreases with increasing temperature. They exhibit strong resistance to hard water, can strongly adsorb on solid surfaces, are compatible with other surfactants such as anionic, cationic, and amphoteric surfactants, and can dissolve in organic solvents. They are non-toxic, non-irritating, and biodegradable, making them a new generation of "green products."
Non-ionic surfactants have various properties such as dispersion, emulsification, foaming, wetting, and solubilization, as well as multiple functions such as washing, antistatic, colloid stabilization, uniform dyeing, and preservation. Besides being extensively used in consumer products such as synthetic detergents and cosmetics, they can also be used as auxiliaries and are widely applied in textile, papermaking, food, plastics, leather, glass, petroleum, chemical fiber, medicine, pesticide, coatings, dyes, fertilizers, film, photography, metal processing, ore beneficiation, building materials, environmental protection, firefighting, and other fields.
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