Emulsifiers are used to maintain a uniform dispersion of one liquid in another, such as oil in water(O/W) or water in oil (W/O) systems. The basic structure of an emulsifying agent includes a hydrophobic portion, usually a long-chain fatty acid, and a hydrophilic portion that may be either charged or uncharged. The hydrophobic portion of the emulsifier dissolves in the oil phase, and the hydrophilic portion dissolves in the aqueous phase. This hydrophilic and hydrophilic portions could vary in different compositions, named as HLB (Hydrophilic Lipophilic Balance). A high value of HLB states more hydrophilic content in an emulsifier. Emulsifiers referred to as surfactants because of reducing surface tension. Thus, surfactants are used in many areas as wetting agents, oil and soil removers, retarders or leveling agents.
Surfactants are classified as:
- Nonionic surfactants: These are the most commonly used emulsifiers for silicones and reduce the surface tension of water from 72 dyn/cm to 29 dyn/cm. Ethoxylated fatty alcohols, alkylphenols, glycerol, and fatty amine ethoxylates are the most common non-ionic surfactants. Generally for the textile industry, nonionic surfactants are used in the formulations because of the process stability.
The main use for nonionic surfactants is the pre-treatment application on textile or fiber. At the same time, some of the formulations can include anionic and nonionic surfactant combinations.
Nonionic emulsifiers are used to emulsify silicone oils. They can be combined in silicone emulsion formulations depending on their HLB. The use of surfactants with 2 or 3 different HLB values increases emulsion stability. The critical point here is to create the surface-active equilibrium at the average required HLB value to emulsify the silicone oil. The most commonly used surfactant type in silicone emulsions are tridecyl alcohols. Silicone emulsions can also be made with surfactants containing different alcohols. The most important issue in the selection of surfactant materials when making silicone emulsion is the emulsion type. The average HLB value is generally lower for macro emulsions than for micro emulsions. The required hydrophilic-lipophilic balance (HLB) of an oily substance indicates the HLB of the surfactants required to prepare a stable emulsion using this oil. The exact required HLB value of silicone oils needs to be defined by using surfactant blends (such as Span 20, Tween 20, vitamin E TPGS, Pluronic F68, Span 60 and Tween 80).
- Anionic surfactants: They are used in cleaning products like detergents and could reduce the surface tension of water from 72 dyn/cm to 23 dyn/cm. Alkane sulfonate, alkyl aryl sulfonate, ethoxylated alcohol sulfates and, fatty acid salts are the frequently used anionic surfactants.
- Cationic surfactants: Quaternary ammonium compounds are used as biocides and retarding agents for cationic dyes.