Emulsification and Demulsification Technology * Selection of Emulsifiers An important step in the production of emulsions is to select suitable emulsifiers from thousands of different commercial emulsifiers. The commonly used emulsifiers are anionic emulsifiers and nonionics. An emulsifier or a combination of the two.
The choice of emulsifier is influenced by a number of factors, first based on the type of emulsion (oil-in-water or water-in-oil), and the emulsifier must be compatible with both the oil and the components of the aqueous phase. When selecting an emulsifier, the oil-in-water emulsion is usually a monovalent soap, and the high-priced soap is used in a water-in-oil system. The application of sodium soap is usually not used because they are too alkaline, when neutral, Will result in a hard soap, the solubility of the soap is limited, potassium salt or more typical alkyl alkanohydrin soap (such as diethanolammonium or triethanolammonium) is lighter and more soluble, stearic acid triethanolammonium salt is applied A wide variety of zui, as an emulsifier, it is cheap and variety, but it will irritate the human skin, become a gel over time, and may form nitrosamine in the product, which reduces this The ubiquity of emulsifier applications.
The choice of emulsifier must also take into account many other factors, such as mild adaptation to the skin, color odor and wettability, while also taking into account the stability of the emulsifier in each phase, the selected emulsifier in at least one phase. It is soluble, and if it is insoluble in any one phase, the emulsion cannot form. Historically, natural materials such as beeswax or lanolin can only form water-in-oil emulsions, which vary in price and emulsifying power depending on the time and the manufacturer.
In the range of nonionic emulsifiers, ethoxylates differ greatly from those that are not ethoxylated, including sorbitan, fatty ethoxylated amines, ethoxylated fatty acids and their esters. Alkylphenol ethoxylates are less selective for cosmetic applications because of the consideration of the safety of these materials for humans, especially for eye and skin. The way to choose an emulsifier is to use the manufacturer's text to add the new product to the formula test. The other method is to use HLB.
Surfactants are multifunctional, their ability to emulsify, the type and stability of the emulsion produced are not only related to the type and concentration of the surfactant, but also to the compatibility between the components of the system. RosenMYers proposed the principle of selecting surfactants with emulsifiers.
(1) It has a high surface activity in the applied system, resulting in a lower interfacial tension, which means that the surfactant must have a tendency to migrate to the interface without remaining in the liquid phase on both sides of the interface. Thus, it is desirable to have a proper balance of the hydrophilic and lipophilic portions of the surfactant, which will cause some degree of deformation of the structure of the two bulk phases. Excessive solubility in any one of the integral phases is disadvantageous.
(2) At the interface, a relatively strong adsorption film must be formed by its own adsorption or other adsorbed molecules. In terms of molecular structure requirements, there should be a large lateral interaction force between the molecules on the interface, which means that in the O/w emulsion, the lipophilic group on the interface film should have a strong side. To interact,
(3) The surfactant must migrate to the interface at a certain speed, so that the interfacial tension of the system during the emulsification process is reduced to a lower value in time. The rate at which a particular emulsifier or emulsifier system migrates to the interface can be varied, depending on whether the emulsifier is added to the oil or water phase prior to emulsification.
In summary, from the perspective of the hydrophilic-lipophilic balance of the emulsifier, the choice of emulsifier should generally be considered as follows; oil-soluble emulsifiers tend to form w/O emulsion, oil-soluble emulsifier and water-soluble emulsifier The mixture produces an emulsion which is superior in quality and stability to the emulsion produced by a single emulsifier. The greater the polarity of the oil phase, the more emulsifier should be. The more non-polar the emulsified oil, the more emulsifier should be. It is more lipophilic.
The second section of HlB value using HLB detection system to choose emulsifier is a widely used method of Zui, an emulsifier HLB value reflects the hydrophilic-lipophilic balance of the water phase interface.
1. Surfactant Hydrophilic-Lipophilic Balance (HLB) Concept This concept has important implications for the selection of a suitable surfactant that will satisfactorily emulsifie a given ingredient into an emulsion at a certain temperature. This means that the hydrophilic-lipophilic balance (HLB) of surfactants is useful in the study of emulsifiers, solubilities, microemulsions and other applications.
The use of this concept for quantification-based approaches has been proposed: the HLB values ​​proposed by Griffin and Davies, the H/L values ​​proposed by Noore and Bell, the water values ​​proposed by Greenwald et al., the HLB temperatures proposed by Shinoda and the assistants (or PIT). , phase inversion temperature), and the EIP (emulsifier phase inversion point) of the nonionic surfactant proposed by Marszall and the HLB composition of the ionic surfactant proposed by Shinoda et al.
In the first three mentioned schemes, the HLB value proposed by Griffin was named HLB (value) method, and the application of Zui was extensive. However, the HLB value is a molecular-related value. For example, the presence of two solvents does not require consideration of their properties, which is not desirable because the HLB of the adsorbed surfactant is at the oil/water interface depending on the type of oil, The temperature, the oil and the additives of the water phase change.
In contrast to these studies, PIT (HLB temperature) is a characteristic property of emulsifiers and surfactants. The influence of additives in solvents, the influence of emulsifier mixtures or oil mixtures, and the influence of molecular structure reflect PIT and tell us emulsifiers. How does the HLB change in the interface? The true HLB of the emulsifier reflects not only the structure and composition of the surfactant, but also the type and temperature of the oil.
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