Hydrophilic-lipophilic balance HLB

Emulsifiers are classified by the hydrophilic—lipophilic balance (HLB) system. This system indicates whether an emulsifier is more soluble in water or oil, and for which type of emulsion (water-in-oil or oil-in-water) it is best suited. Emulsifiers having alow HLB value are more oil soluble, and are better suited for water-in-oil appHcations such as margarine. Conversely, emulsifiers having a high HLB value are more water soluble, and function more effectively in oil-in-water emulsions such as ice cream (34). The use of this system is somewhat limited because the properties of emulsifiers are modified by the presence of other ingredients and different combinations of emulsifiers are needed to achieve a desired effect. The HLB values of some common emulsifiers are given (35). 

One of the most important characteristics of the emulsifier is its CMC, which is defined as the critical concentration value below which no micelle formation occurs. The critical micelle concentration of an emulsifier is determined by the structure and the number of hydrophilic and hydrophobic groups included in the emulsifier molecule. The hydrophile-lipophile balance (HLB) number is a good criterion for the selection of proper emulsifier. The HLB scale was developed by W. C. Griffin [46,47]. Based on his approach, the HLB number of an emulsifier can be calculated by dividing... 

These characteristics are typically classified as a hydrophile-lipophile balance (HLB value). For example, hydrophilicity may be denoted within a range of 2 to 20, with true solutions being obtained at HLB values >14 and poor dispersibility occurring at HLB values <6. Oil-in-water emulsification requires a high HLB value surfactant, while water-in-oil emulsification needs a low HLB value surfactant. 

Cleaning solution formulations may include one or more deposit removers, plus an appropriate corrosion inhibitor (to protect exposed metal). An antifoam and often a wetting agent [e.g., an alkylarylpoly-ethoxy alcohol with a 12-15 hydrophilic-lipophilic balance (HLB) to improve detergency and solubilization] may also be added. 

The performance of secondary alkanesulfonates in applications as emulsifiers in the widespread emulsion polymerization of vinyl monomers can be assessed by their hydrophilic-lipophilic balance (HLB) numbers. The HLB numbers can... 

Formation of emulsions of the oil-in-water or water-in-oil type depends mainly on the hydrophilic-lipophilic balance (HLB) of the emulsifier. Phosphate esters with their various molecular structures can be adjusted to nearly every HLB value desired. Therefore they are able to meet nearly all of demands in this field. 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Particularly useful is the physical classification of surfactants based on the hydrophile-lipophile balance (HLB) system [67,68] established by Griffin [69,70]. More than 50 years ago he introduced an empirical scale of HLB values for a variety of nonionic surfactants. Griffin s original concept defined HLB as the percentage (by weight) of the hydrophile divided by 5 to yield more manageable values ... 

It is possible to modify the matrix hydrophilicity-lipophilicity balance (HLB) by using different alkyl-modified trialkoxysilanes as co-reagents with tetraethylorthosilicate (TEOS), to greatly alter (reduce) the release rate of heparin, as then water access to the entrapped drug is considerably reduced (Figure 2.10).4... 

Hydrophilic-lipophilic balance (HLB), 24 143, 155-156 in paper recycling, 21 436 Hydrophilic-lipophilic balance temperature, 16 430... 

The two media typically used include Simulated Gastric Fluid (pH 1-pH 3) and Simulated Intestinal Fluid (pH 6-pH 7). The drug substance under investigation is introduced, and its uptake in the diffusion cell ( absorption ) is governed by its hydrophilic-lipophilic balance (HLB). The absorption model proposed by Strieker (26) in the early 1970s therefore effectively took into consideration (in an experimental sense) all aspects considered by the theory of the BCS, which was introduced more than 20 years later. 

On a more practical level, to use CLAs and CGAs in PDSE it is important to understand the influence of key parameters such as solvent type and polarity, and surfactant type (hydrophilic/lipophilic balance, HLB) and concentration, on the formulation and stability of CLAs and CGAs. These are discussed next. 

Lipids with a suitable hydrophilic-lipophilic balance (HLB) are known to spread on the surface of water to form monolayer films. It is obvious that if the lipid-like molecule is highly soluble in water, it will disappear into the bulk phase (as observed for SDS). Thus, the criteria for a monolayer formation are that it exhibits very low solubility in water. The alkyl part of the lipid points away from the water surface. The polar group is attracted to the water molecules and is inside this phase at the surface. This means that the solid crystal, when placed on the surface of water, is in equilibrium with the him spread on the surface. A detailed analysis of this equilibrium has been given in the literature (Gaines, 1966 Adamson and Gast, 1997 Birdi, 2009). The thermodynamics allows one to obtain extensive physical data on this system. It is thus apparent that, by studying only one monolayer of the substance, the effect of temperature can be very evident. 

The key-step of the synthesis of glycolipids, and more generally of amphiphilic carbohydrates, is the covalent coupling of a hydrophilic carbohydrate with a lipophilic compound. A hydrophilic or hydrophobic spacer may be inserted between them in order to control the hydrophilic-lipophilic balance (HLB). This modulation allows to obtain variously organized systems with the same polar head and apolar tail. 

Bourrel M, Chambu C (1983) The Rules for Achieving High Solubilization of Brine and OU by AmphiphUic Molecules. Soc Petrol Eng J 23 327-338 Kunieda H, Shinoda K (1985) Evaluation of the hydrophile-lipophile balance (HLB) of nonionic surfactants I. Multisurfactant systems. J Colloid Interface Sci 107 107-121 Kahlweit M, Strey R, Eirman P (1986) Search for tricritical points in ternary systems Water-oil-nonionic amphiphile. J Phys Chem 90 671... 

Nonionic surfactants are often characterized in terms of their hydrophile—lipophile balance (HLB) number (see Emulsions). For simple alcohol... 

Molecules consisting of a long hydrophobic part and one or two hydrophilic headgroups. Able to form micelles and/or liposomes depending on the hydrophilic-lipophilic balance (HLB). 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubility in water is extremely small. At some intermediate temperature, the hydrophile—lipophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic liquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the following manner. Equal amounts of the oil and the aqueous phases with all the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

Griffin suggested an empirical quantitative hydrophile-lipophile balance (HLB) scale which characterizes the tendency of a surfactant to form water-in-oil or oil-in-water emulsions [544], The HLB is a direct measure of the hydrophilic character of a surfactant the... 

The hydrophilic-lipophilic balance (HLB) classi Lcation system was L rst introduced by GrifL n (1949) to characterize the relative afLnity of a surfactant to the aqueous and oil phase. A HLB value is an empirical numerical value in the range of 1-30. The higher the HLB value, the more hydrophilic the surfactant is and in turn, the lower the HLB value, the more lipophilic the surfactant is. As a result, surfactants with higher HLB values (>8) are favorable for formation of o/w emulsions, while surfactants with lower HLB values (3-6) are more suitable for the formation of w/o emulsions. The HLB values of the surfactants used in parenteral emulsions are listed in Table 10.2. 

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