Hydrophile-lipophile characteristics

An anionic mlcroemulslon system was based on blends of monoethanolamlne salts of bilinear dodecyl benzene sulfonic acid and branched pentadecyl o-xylene sulfonic acid. The bilinear structure results from the alkylation of benzene with a linear a-olefin. The former acts as a surfactant hydrophile (H) while the latter acts as a surfactant lipophile (L) at room temperature for the oil and water phases used in this study. The hydrophile tends to form water-continuous emulsions while the lipophile forms oil-continuous emulsions. The hydrophile-lipophile characteristics were varied by changing the weight ratio of H/L from 0.5 to 0.8. Decane was used as the oil phase and 2.0 wt. X NaCl In water as the aqueovis phase. The water-oil ratio was fixed at 95/5 and the total surfactant content was fixed at 2 g/dl. 

In an effort to investigate the universality of this t rpe of polymer-microemulsion interaction, an anionic surfactant system was studied. Two sulfonate surfactants were chosen to enable variation of the hydrophile-lipophile characteristics of the surfactant couple and in turn of the mlcroemulslon. The... 

There are a large number of emulsifiers available and making a choice for a new formulation or product is difficult. The use of the hydrophilic-lipophilic balance (HLB) concept originated by Griffin in 1949 can be a useful empirical method of preliminary selection. The HLB number quantifies the balance of hydrophilic-lipophilic characteristics of the surfactant molecule on an arbitrary numerical scale. The least hydrophilic surfactants are assigned the lowest HLB (see Table 14.2). The use of the HLB balance is also well described by Davies and Rideal. ... 

Skin. The skin may become contaminated accidentally or, in some cases, materials may be deHberately appHed. Skin is a principal route of exposure in the industrial environment. Local effects that are produced include acute or chronic inflammation, allergic reactions, and neoplasia. The skin may also act as a significant route for the absorption of systemicaHy toxic materials. Eactors influencing the amount of material absorbed include the site of contamination, integrity of the skin, temperature, formulation of the material, and physicochemical characteristics, including charge, molecular weight, and hydrophilic and lipophilic characteristics. Determinants of percutaneous absorption and toxicity have been reviewed (32—35,42,43,46—49). 

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. 

Oligopeptides in the Monoolein-Water System. Most oligopeptides are amphiphilic molecules, i.e. they have both hydrophilic and lipophilic characteristics,... 

Especially in the case of high-molecular-weight surface-active substances (such as proteins), the period of change may be sufficiently prolonged to allow easy observation. This arises because proteins are surface active. All proteins behave as surface-active substances because of the presence of hydrophilic-lipophilic properties imparted from the different polar, such as glutamine and lysine, and apolar, such as alanine, valine, phenylalanine, isovaline, amino acids. Proteins have been extensively investigated as regards their polar-apolar characteristics as determined from surface activity. 

The property of interest to characterize a surfactant or a mixture of surfactants is its hydrophilic-lipophilic tendency, which has been expressed in many different ways through a variety of concepts such as the hydrophiUc-lipophilic balance (HLB), the phase inversion temperature (PIT), the cohesive energy ratio (CER), the surfactant affinity difference (SAD) or the hydrophilic-lipophilic deviation (HLD) [1], which were found to be more or less satisfactory depending on the case. In the next section, the quantification of the effects of the different compounds involved in the formulation of surfactant-oil-water systems will be discussed in details to extract the concept of characteristic parameter of the surfactant, as a way to quantify its hydrophilic-lipophilic property independently of the nature of the physicochemical environment. 

In certain cases, cholesterol is required for vesicle formation. It is commonly accepted that the hydrophilic lipophilic balance (HLB) is a parameter that could indicate the vesicleforming potential of surfactants. For amphiphils such as sorbitan esters and alkyl ethers, low HLB values could predict vesicle formation [52,55]. However, niosomes were obtained from polysorbate 20 (HLB 16.7), a highly hydrophilic molecule, when cholesterol at an appropriate concentration was added to the amphiphil [44], In this case it could be assumed that a kind of amphiphilic complex with a lower HLB was responsible for the vesicle formation. An excellent review on the structure, characteristics, chemical composition, and mechanism of action of niosomes was published by Uchegbu and Vyas [41]. 

Since the cornea exhibits hydrophilic as well as lipophilic characteristics, it represents an effective barrier for diffusion of both hydrophilic and lipophilic substances [3,13],... 

The physicochemical characteristics of the foam films and the foam are in good agreement. Thus, Xr for foams stabilised by the members of the homologous series of oxyethylated dodecyl alcohol does not change after n > 10, which is in accordance with the Cw(n) dependence. The effect of the hydrophilic-lipophilic balance on the foaming ability of surfactants will be treated in Section 7.9. 

Since most membranes are lipophilic in nature, a lead has to have some lipophilic characteristics in order to diffuse effectively into and across the membrane. However, in order to reach the membrane, the lead has to be dissolved in the surrounding medium, which is aqueous. Thus the lead also needs some hydrophilic properties in order to have sufficient aqueous solubility to be transported to the membrane. An estimate of a lead s ability to have both the lipophilic and hydrophilic characteristics necessary for effective delivery, primarily from the GI tract, can be determined from the chemical structure of the compound and using what is commonly called Lipinski s Rules of Five, which are four rules with cutoff numbers that are 5 or multiples of 5. These rules are... 

A book by Laugh in [76] is a very valuable reference on the aqueous phase behavior of surfactants. It covers this vast area of science from the viewpoints of the role of phase science within physical science, physical chemistry (thermodynamics of immiscibility, phase diagrams, the phase rule, characteristic features of surfactant phase behavior, kinetic and mechanistic aspects of surfactant phase behavior, relative humidity), structures and properties of surfactant phases, molecular correlations (surfactant and nonsurfactant behavior in amphiphilic molecules, hydrophilicity, lipophilicity, proximate and remote substituent effects, influence of third components on aqueous surfactant phase behavior), the relationship of the physical science of surfactants to their utility, and the history of surfactant phase science. 

Among various ways used to describe the ability of surfactants to stabilize direct and inverse emulsions, the semi-empirical characteristic of hydrophile - lipophile balance (HLB) of surfactant molecules is the one that is most commonly used [46,47]. 

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