Lipophilicity-hydrophilicity

Knowledge of the spatial dimensions of a molecule is insufficient to imderstand the details of complex molecular interactions. In fact, molecular properties such as electrostatic potential, hydrophilic/lipophilic properties, and hydrogen bonding ability should be taken into account. These properties can be classified as scalar isosurfaces), vector field, and volumetric properties. 

COLORANTS FORFOOD,DRUGS,COSTffiTICS AND TffiDICALDEVICES] (Vol 6) HLB. See Hydrophile-lipophile balance. 

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). 

Emulsifiers. Removing the remover is just as important as removing the finish. For water rinse removers, a detergent that is compatible with the remover formula must be selected. Many organic solvents used in removers are not water soluble, so emulsifiers are often added (see Emulsions). Anionic types such as alkyl aryl sulfonates or tolyl fatty acid salts are used. In other appHcations, nonionic surfactants are preferred and hydrophilic—lipophilic balance is an important consideration. 

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) nonionic surfactants. 

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. 

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... 

Alkylphenol ethoxylates (APEOs) are a class of surfactants that have been used widely in the drilling fluid industry. The popularity of these surfactants is based on their cost-effectiveness, availability, and range of obtainable hydrophilic-lipophilic balance values [693]. Studies have shown that APEOs exhibit oestrogenic effects and can cause sterility in some male aquatic species. This may have subsequent human consequences, and such problems have led to a banning of their use in some countries and agreements to phase out their use. Alternatives to products containing APEOs are available, and in some cases they show an even better technical performance. 

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]. 

When an aqueous phase (noted w) is brought in contact with a second immiscible phase (noted o), the different species dissolved in one or the two phases spontaneously distribute depending on their hydrophilic-lipophilic balance until the thermodynamic equilibrium is reached. The distribution of the charged species generates an interfacial region, in which the electrical field strength differs from zero, so that an electrical Galvani potential difference, is established across the interface ... 

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 ... 

H Schott. Solubility parameter and hydrophilic lipophilic balance of nonionic surfactants. J Pharm Sci... 

Hydrophilic-lipophilic balance Electric charge < Solubility Molecular size... 

Methods of controlling surface behavior are to 1. create polar and nonpolar regions in the molecule thus producing a hydrophilic-lipophilic balance in the molecule, 2. charge the... 

Ethoxylated fatty alcohols and alkylphenols were used. The products available on the market make up homologous series containing an average of between 3 and 100 ethylene-oxide groups. They thus have a wide HLB (hydrophilic/lipophilic balance) range. Besides, they are among the least expensive surfactants on the market. 

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