(I) Modified silicone oil
"Modified silicone oil refers to a special silicone oil in which part of the methyl groups in the methyl silicone oil molecule are replaced by various organic groups, and the organic groups and dimethyl silicone oil have the performance of mutual influence." In fact, according to different application needs, there are more copolymer products composed of two or more groups on the same silicon-oxygen main chain. There is no clear boundary between "reactive silicone oil" and "non-reactive silicone oil". If the active group of "reactive silicone oil" is blocked, it loses its reactivity. On the contrary, non-active silicone oil, such as polyether silicone oil, has reactive activity if it contains unblocked hydroxyl groups.

(II) Surfactants
1. The concept of surfactants
Any pure liquid under certain conditions has surface tension. At 20°C, the surface tension of water is 72.75mN·m-1. When a solute is dissolved in a solvent, the surface tension of the solution changes due to the addition of the solute. The magnitude of the surface tension of the aqueous solution changes with different solutes. For example, some inorganic salts can slightly increase the surface tension of water, some low-level alcohols can slightly reduce the surface tension of water, and soap and washing powder can significantly reduce the surface tension of water. The property of reducing the surface tension of a liquid is called surface activity. Surfactants refer to substances with strong surface activity that can significantly reduce the surface tension of a liquid. In addition, as a surfactant, it should also have application properties such as solubilization, emulsification, wetting, decontamination, sterilization, defoaming and foaming, which is an important difference from general surfactants.

2. Structural characteristics of surfactants
Surfactant molecules are generally composed of a non-polar hydrocarbon chain and one or more polar groups, and the length of the hydrocarbon chain is generally more than 8 carbon atoms. The polar group can be a dissociated ion or a non-dissociated hydrophilic group. Polar groups can be carboxylic acids and their salts, sulfonic acids and their salts, sulfates and their soluble salts, phosphates, amino or amines and their salts, or hydroxyl groups, amide groups, ether bonds, carboxylate groups, etc. For example, soap is a fatty acid (R-COO-) surfactant, in which the fatty acid carbon chain (R-) is a lipophilic group and the dissociated fatty acid radical (COO-) is a hydrophilic group.

3. Adsorption of surfactants
(1) Positive adsorption of surfactant molecules in solution
When surfactants are dissolved in water, when the concentration of surfactants in water is very low, surfactant molecules are oriented at the water-air interface, with the hydrophilic groups facing the water and the lipophilic groups facing the air. When the solution is dilute, the surfactants are almost completely concentrated on the surface to form a monolayer. The surfactant concentration on the surface layer of the solution is much higher than the concentration in the solution, and the surface tension of the solution is reduced to below the surface tension of pure water. The phenomenon of surfactants gathering on the surface layer of the solution is called positive adsorption. Positive adsorption changes the properties of the solution surface, and the outermost layer presents hydrocarbon chain properties, thereby showing lower surface tension, and then producing better wettability, emulsification, foaming, etc. If the surfactant concentration is lower and the surface tension is reduced more significantly, the surface activity is stronger and the easier it is to form positive adsorption. Therefore, the surface activity of the surfactant is of great significance to its practical application.
(2) Adsorption of surfactants on solid surfaces
When the surfactant solution comes into contact with the solid, the surfactant molecules may be adsorbed on the solid surface, causing the solid surface properties to change. The adsorption curve of polar solid substances on ionic surfactants is S-shaped at low concentrations, forming a monolayer, and the hydrophobic chains of the surfactant molecules extend to the air. When the surfactant solution concentration reaches the critical micelle concentration, the adsorption reaches saturation. At this time, the adsorption is double-layer adsorption. The arrangement direction of the surfactant molecules is opposite to that of the first layer, and the hydrophilic groups point to the air. Increasing the solution temperature will reduce the adsorption amount. For non-polar solids, only monolayer adsorption generally occurs, with the hydrophobic group adsorbed on the solid surface and the hydrophilic group pointing to the air. When the surfactant concentration increases, the adsorption amount does not increase or even tends to decrease. The adsorption of nonionic surfactants on the solid surface is similar to the above, but its adsorption amount increases with increasing temperature, and it can change from monolayer adsorption to multilayer adsorption.
(3) Silicone surfactants
"Reactivity" and "surface activity" are two different concepts. In layman's terms, the so-called "reactivity" refers to the ability of this material to form molecular bonds with other material products. "Surface activity" refers to the "hydrophilic" and "lipophilic" properties of the material.
According to the surface activity characteristics of chemicals, any methyl group in polydimethylsiloxane (PDMS) replaced by a carbon functional group compound, such as polyether, amino, epoxy, carboxyl, quaternary ammonium, phosphate or a copolymer composed of two groups on the same silicon-oxygen main chain, can be regarded as a silicone surfactant.
"Silicone surfactants" are a new type of additive that has been active in the domestic material industry market in the past decade. The reason for the rapid development of silicone surfactant product development, production and application is the rapidly developing market demand, as well as the widespread use of imported products with excellent performance and application formula technology in China. Among them, polyether-grafted polydimethylsiloxane (PDMSOPE), referred to as polyether silicone oil, is a typical one.

2. Characteristics of silicone surfactants
1. Surface activity and easy spreading (low surface tension)
The important characteristics of silicone surfactants are their excellent surface activity and easy spreading. This characteristic comes from the low surface tension and weak intermolecular force of polydimethylsiloxane. The silicon atom is at the center of the tetrahedron in the compound. According to the tetrahedral structure, the two methyl groups are perpendicular to the plane connecting silicon and two adjacent oxygen atoms; due to the large SI-C bond length, the three hydrogens on the two non-polar methyl groups are like an open umbrella, which makes it very hydrophobic.
The three hydrogen atoms on the methyl group occupy a large space due to the rotation of the methyl group, thereby increasing the distance between adjacent siloxane molecules; the intermolecular force is inversely proportional to the sixth power of the intermolecular distance, so the intermolecular force of polydimethylsiloxane is much weaker than that of hydrocarbons. Therefore, its surface tension is smaller than that of hydrocarbons with similar molar mass, making it easy for siloxane to spread on the interface. Another reason why polydimethylsiloxane chains are easy to spread on polar surfaces (such as water, metal, fiber, etc.) is that the oxygen in the silicon oxygen chain can form hydrogen bonds with polar molecules or atomic groups, increasing the molecular force between the silicon oxygen chain and the polar surface, prompting it to spread into a monolayer; thus, the hydrophobic siloxane lies horizontally on the polar surface, presenting a unique "extended chain" configuration. The hydrophobic base of ordinary surfactants stands upright on the polar surface.
The above characteristics of silicone surfactants determine that this type of substance has the characteristics of easy emulsification, excellent permeability, firm bonding with polar substrates, good surface spreading, and thin film formation. If the hydrophilic group is not modified, it still has the characteristics of hydrophobicity.

2. Temperature resistance and hydrolysis resistance
The hydrophilic group in the silicone surfactant cannot be directly connected to the silicon atom of the siloxane chain. The hydrophilic group directly connected to the silicon is easily hydrolyzed to form a silanol group, which can further condense or cross-link, thereby completely destroying the chemical structure of the silicone surfactant. Therefore, the synthesis of silicone surfactants must connect the hydrophobic group and the hydrophilic group through an isolating group. According to the difference in the connecting groups of the hydrophobic group and the hydrophilic group, polyether silicone oil can be divided into two types: silicon-oxygen-carbon chain-hydrophilic group type and silicon-carbon-hydrophilic group type. The former is usually used as a foaming agent in the polystyrene foaming process, also called "hydrophilic silicone oil". Silicon-oxygen-carbon chain-hydrophilic group type polyether silicone oil is usually not suitable for use in the presence of water, because the SI-O-C bond is easily hydrolyzed and condensed, resulting in the destruction of the structure and disappearance of the silicone surfactant, and it is not resistant to high temperatures. Silicon-carbon-hydrophilic silicone surfactants are stable in water and will not hydrolyze. They can be used for a long time below 150°C; in a short time, they can also reach 200°C.

3. Hydrophilicity
The typical type of silicone surfactant is polyether silicone oil. Because polyether groups are suspended or blocked on its molecular chain (side chain or main chain), it has both lipophilic and hydrophilic properties. That is, the oil is not only miscible with alkane oily substances, but also easily dispersed in water. This is a property with great application value.

3. Application of silicone surfactants
In addition to the wetting, dispersing, foaming, defoaming, antistatic, emulsifying, penetrating, soft, lubricating, and solubilizing properties of ordinary surfactants, silicone surfactants also have high surface activity, easy spreading, physiological inertness, weather resistance, and high temperature resistance. These characteristics make it very suitable for plastics, rubbers, etc.