Classification of Wetting Agents and the Wetting Effect of Surfactants

Aug 3, 2021

1. According to the strength of the role, it can be divided into two categories:
(1) Solvents with low surface tension and water miscibility, including ethanol, propylene glycol, glycerin, dimethyl sulfoxide, etc.
(2) Surfactants, such as anionic surfactants, certain polyol type surfactants (Spanish type), polyoxyethylene type surfactants (Tween type)

2. According to the route of administration, it can be divided into three categories:
(1) Wetting agents used in external preparations include surfactants and alcohols that have low surface tension and are miscible with water.
(2) Wetting agents used in oral preparations include ethanol, glycerin, Tween, etc., which have low surface tension and are miscible with water.
(3) Wetting agents for injection administration, including ethanol, propylene glycol, glycerin, polyethylene glycol 200 400, etc., and Tween-80, which have low surface tension and are miscible with water.
3. Divided into two categories according to the nature:Wetting agents include anionic and nonionic surfactants.:Anionic surfactants include alkyl sulfates, sulfonates, fatty acid or fatty acid ester sulfates, carboxylic acid soaps, phosphate esters, and the like.Nonionic surfactants include polyoxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, polyoxyethylene polyoxypropylene block copolymers and the like.

At present, there is also a newest type of silanol non-ionic surfactant on the market, also called wetting agent. Features: low molecular weight, multi-hydrophobic groups with umbrella-shaped symmetric structure, compared with traditional active agents, wetting and penetrating It has excellent performance and high efficiency, and it is a revolutionary new-generation surfactant. Dynamic and static surface tension is extremely low, containing dihydroxy, reactive activator, chemically inert, generally does not participate in the chemical reaction of the system, good acid and alkali resistance, stable chemical properties.

Wetting agents are also a kind of surfactants. Wetting properties are one of the properties of surfactants, but the structure of the surfactants is different, which determines the effect of the surfactant's wetting properties. Surfactants with high wettability generally have the following properties. The carbon chain should not be linear and has a certain branched structure, that is, the isomeric type has better wettability than the linear type, and other properties can be See books about surfactants, all of which are explained above!
When the solid is in contact with the liquid, the original solid/gas, liquid/gas interface disappears and a new solid/liquid interface is formed. This process is called wetting. For example, textile fiber is a porous material with a huge surface. When the solution spreads along the fiber, it will enter the interstices between the fibers and drive out the air, turning the original air/fiber interface into a liquid/fiber interface. , Is a typical wetting process: while the solution enters the fiber at the same time, this process is called penetration. Surfactants that help wetting and penetration are called wetting agents and penetrants.

By dropping different liquids on the same solid surface, two different phenomena can be seen. One is that the liquid droplets spread out quickly on the solid surface to form a new liquid interface. This situation is called wetting. The angle between the gas-liquid interface passing through the liquid and the solid-liquid interface is called the contact angle. The contact angle is less than 90° when wet. Another situation is that the liquid does not spread on the solid surface, but shrinks into a drop on the solid surface, such as the phenomenon formed by adding water droplets to the surface of the paraffin wax. This situation is called non-wetting, as shown in Figures (c) and Figures. As shown in (d), the contact angle at this time is greater than 90°.