Hydrophilic-lipophilic balance system

HLB (hydrophile-lipophile balance) system, 70 126 HLB value, 72 54, 55 HMG-CoA, role in cholesterol synthesis, 5 142... 

Hydronium ion, 14 23 Hydroperoxidates, 18 411 Hydroperoxide process, for propylene oxide manufacture, 20 798, 801-806 Hydroperoxides, 14 281, 290-291 18 427-436 alkylation of, 18 445 a-oxygen-substituted, 18 448-460 chemical properties of, 18 430 433 decomposition of, 14 279 18 431-432 liquid-phase epoxidation with, 10 656 physical properties of, 18 427-430 preparation by autoxidation, 18 434 synthesis of, 18 433-435 Hydrophile-lipophile balance system,... 

H. Schott, Comments on Hydrophile-Lipophile Balance Systems, J. Pharm. Sci., 19, 87 (1990). 

The initial step in the fabrication of a multiple emulsion (W/OAV) is to prepare a primary emulsion (W/0). It is generally agreed that the surfactant for the primary emulsion should have an HLB value of 3-6 (in the hydrophilic-lipophilic balance system of surfactant classification). Surfactants that have successfully been utilized include Span 80 (sorbitan oleate Nianxi et al, 1992 Zheng et al, 1993 Omotosho et al, 1990), E644 (polyamine Nianxieia/., 1992),N205 (polyamine Nianxi eta/., 1992), TX-4 (polyoxyethylene aUcylphenol ether Nianxi et al, 1992), MO A3 (polyoxyethylene aliphatic alcohol ether Nianxi et al, 1992), Brij 93 (Nianxi et al, 1992), polyoxamers [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer Law et al, 19861, and egg lecithin. The surfactant or combination of surfactants is then dissolved in the oil... 

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). 

Phase transfer catalysis (PTC) refers to the transfer of ions or organic molecules between two liquid phases (usually water/organic) or a liquid and a solid phase using a catalyst as a transport shuttle. The most common system encountered is water/organic, hence the catalyst must have an appropriate hydrophilic/lipophilic balance to enable it to have compatibility with both phases. The most useful catalysts for these systems are quaternary ammonium salts. Commonly used catalysts for solid-liquid systems are crown ethers and poly glycol ethers. Starks (Figure 4.5) developed the mode of action of PTC in the 1970s. In its most simple... 

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 ... 

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... 

The temperature (or salinity) at which optimal temperature (or optimal salinity), because at that temperature (or salinity) the oil—water interfacial tension is a minimum, which is optimum for oil recovery. For historical reasons, the optimal temperature is also known as the HLB (hydrophilic—lipophilic balance) temperature (42,43) or phase inversion temperature (PIT) (44). For most systems, all three tensions are very low for Tlc < T < Tuc, and the tensions of the middle-phase microemulsion with the other two phases can be in the range 10 5—10 7 N/m. These values are about three orders of magnitude smaller than the interfacial tensions produced by nonmicroemulsion surfactant solutions near the critical micelle concentration. Indeed, it is this huge reduction of interfacial tension which makes micellar-polymer EOR and its SEAR counterpart physically possible. 

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. 

Microemulsions are transparent or translucent, thermodynamically stable emulsion systems (Griffin 1949). Forming a middle phase microemulsion (MPM) requires matching the surfactant system s hydrophobicity with that of the oil. The HLB (hydrophilic-lipophilic balance) number reflects the surfactant s partitioning between water and oil phases higher HLB values indicate water soluble surfactants while lower values indicate oil soluble surfactants (Kunieda et. al. 1980, Abe et. al. 1986). While a balanced surfactant system produces middle phase microemulsions, an underoptimum surfactant system is too water soluble (high HLB) while an over-optimunTSystem is too oil soluble (low HLB). 

Neumann and Miller (360) reported catalytic epoxidations with analogous P-W materials in a triphasic mode. The activity in the solvent-free system is influenced by the length of the hydrocarbon spacer between the silica and the ammonium group. Cyclooctene, for example, is epoxidized with only 10% conversion when a trimethyl propyl ammonium salt is used, whereas a conversion of 45% can be obtained in the presence of an immobilized octyldimethyl benzyl ammonium salt. The enhanced conversion is probably the result of a nearly ideal hydrophilic-lipophilic balance at the active site. 

The solubility of the surfactant of polyethyleneglycol type in different phases can be described by the HLB (hydrophilic-lipophilic-balance) concept [ 27]. This concept attributes to the molecule a HLB number that represents the geometric ratios of the hydrophilic and the hydrophobic moieties. It should, however, be emphasized that the HLB does not represent a fundamental property of the system but is based on experience. For fatty alcohol ethoxylates... 

The hydrophile-lipophile balance (HLB) system is the measure of the surfactant s polarity as well as other physical properties of surfactants and the emulsifying materials. The more lipophilic the surfactant is, the lower the HLB values will be. Table 4.5 empirically classifies and compares surfactants according to their optimum use. Table 4.6 shows the HLB values for a selected group of surfactants. The HLB value of the surfactant or surfactant mixture should be matched with that of the oil or the mixture of oils to ensure a stable emulsion. The required HLB values of a... 

An emulsifier system must cause the concentrate to disperse spontaneously into small, stable droplets when mixed with water. To accomplish this, the surfactant system must have a most favorable solubility relationship a proper balance between oil and water solubility or, in other words, a favorable hydrophile-lipophile balance in solubility. This balance in solubility is frequently referred to as HLB and was first described by Griffin (6). However, the HLB system is based on the structure of a surfactant molecule and, therefore, predicts the behavior of a single molecule. It does not take into account tr 3 fact that many surfactants form micelles in organic solutions. If a micelle is formed, its HLB may have no relationship to the HLB of the monomer unit. Therefore, to select an emulsifier well, we will need a better understanding of the behavior of surfactants in organic solvents. 

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