Hydrophilic-lipophilic behavior

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... 

The plots of log k vs. log P w and the plots of log k (v) vs. log k (z) were studied for seven cephalosporins. A linear relationship was obtained in micellar solution and in microemulsion solution (Tables 3 and 4). The results obtained indicate that the capacity factor determined by EKC could be used both as parameter to characterize the partition behavior of drugs in ME and MC and as hydrophobic parameter instead of log Pow. k appears to be an evident parameter, and it shows a better diversification than P w. In the 1-octanol/water system, we did not found high values of the partition coefficients. In contrast, the ME systems used provide a better characterization of the drugs according to their hydrophilic/lipophilic properties. 

In addition to lowering surface tension, surface-active agents contribute to emulsion stability by oriented adsorption at the interface and by formation of a protective film around the droplets. Apparently, the first molecules of a surfactant introduced into a two-phase system act to form a monolayer additional surfactant molecules tend to associate with each other, forming micelles, which stabilize the system by hydrophilic-lipophilic arrangements. This behavior has been depicted by Stutz et al. ( ) and is shown in Figures 1-5. 

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. 

A frequently used method is known as the HLB (hydrophile-lipophile balance) method. In this method (Griffin, 1949), a number (0-40) indicative of emulsification behavior and related to the balance between the hydrophilic and lipophilic (hydrophobic) portions of the molecule has been assigned to many commercial emulsifying agents. (In some cases, the HLB number is calculated from the structure of the molecule in other cases, it is based on experimental emulsification... 

Kunieda, H. and Shinoda, K. (1982) Phase behavior in systems of non-ionic surfactant-water-oil around the hydrophile-lipophile balance temperature (HLB-temperature). /. Dispersion Sci. Technol, 3, 233-244. 

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. 

Based on the complementarity, double-looped crownophane 40 is expected to transport isophthalic acid (m-PA) most efficiently among other isomers with almost the same hydrophilic-lipophilic balance (HLB) values. Results in Table 10 show that the largest transport efficiency was observed for m-PA and phthalic acid (o-PA), and, as expected, the longest terephthalic acid (p-PA) was not transported so well. Consequently, their transport behavior largely depends on the distance between two crown moieties in the host molecules and that of two carboxylate groups in the guest molecules. 

H Kunieda, K Hanno, S Yamaguchi, K Shinoda. The three-phase behavior of a brine/ionic surfactant/non-ionic surfac-tant/oil system Evaluation of the hydrophile—lipophile balance (HLB) of ionic surfactant. J CoUoid Interface Sci 107 129, 1985. 

Nowadays, partially or fuUy fluorinated surfactants are available with a variety of chemical structure and chain lengths. Therefore hydrophilic-lipophilic properties can be controlled and these new surfactant molecules may provide a rich phase behavior, which could be used to obtain well-organized mesoporous materials. 

Kunieda, H., and Shinoda, K. (1980) Solution behavior and hydrophile-lipophile balance temperature in aerosol OT/isooctane/brine system correlation between microemulsions and ultralow interfacial tensions. J. Colloid Interface Sci., 75, 501-505. 

In total, a corrosive is not exclusively an acid or a base. Other molecular reactive functions can develop, as we have just seen, an aggressive character toward the skin. A corrosive is not a substance only soluble in water as is the case of fatty amines or with some fatty acids, for example. This type of molecules can also present an amphiphilic character. One pole is hydrophilic and the other lipophilic. These properties are useful to classify the behavior and the effectiveness of emulsifiers. This is the concept of hydrophilicity/lipophilicity balance (HLB). The more the value is high (scale from 1 to 40), the more the emulsifier is hydrophilic. These concepts are also used to justify suitable and efficient conditions of washing skin splashes. 

A tenside with a relatively strong lipophilic group and weak hydrophilic group is mainly soluble in oil and preferentially stabilizes a w/o emulsion, and vice versa. This fact led to the development of a standard with which the relative strength or activity of the hydrophilic and lipophilic groups of emulsifiers can be evaluated. It is called the HLB value (hydrophilic-lipophilic balance). It can be determined, e. g., from dielectric constants or from the chromatographic behavior of the surface-active substance. The HLB value of the fatty acid esters of polyhydroxy alcohols can also be calculated as follows (SV =... 

In order to understand the behavior of an amphiphile in terms of partial structure functions in a ternary system, we consider the interaction energy parameter C, characterizing the imbalance of amphiphilicity defined by Gompper and Schick [9, 10], which is the difference between the interaction of amphiphile with water and oil. Hence, one would expect C = 0 at the hydrophile-lipophile balance (HLB) line, amphiphile favors oil to water for C > 0 and the opposite holds for C < 0. C has an interesting role in the phase diagram. For equal volume fractions of water and oil (5(t) = — < > 0) and C = 0, the phase diagram... 

Mixtures of two or more svufactants have been used very often to attain some average property with more or less success. The early hydrophilic-Upophilic balance (HLB) rule of formulation assumes that the surfactant mixture at the interface (i.e., the one that produces the result) depends linearly on the mixture composition in the system. This implicitly assumes that there is some kind of collective behavior among all surfactants (i.e., that all surfactant species partition in the same way in all phases and at the interface). This approximation is known to be valid when similar surfactants are mixed, particularly from the hydrophilic—lipophilic tendency point of view [85,86]. However, if a very hydrophiUc surfactant is mixed with a very lipophilic one, there is not necessarily an intermediate hydrophilicity mixture at the interface. In many cases, the most hydrophilic surfactant will partition mostly in water, whereas the most lipophilic one will fractionate into the oil phase, so that they may leave a leftover surfactant mixture of unpredictable hydrophilicity at the interface [46,49]. For example, it has been shown that sometimes a hydrophilic result is attained by adding a lipophilic surfactant, by the so-called retrograde transition [87,88] phenomenon. 

In fact, the phase behavior and interfacial tension of snch alkyl polyglycoside emulsifier systems closely resemble those of conventional fatty alcohol ethoxylate systems if temperatnre as a key phase behavior parameter is replaced by the mixing ratio of the hydrophilic/lipophilic emnlsihers in the non-ethoxy-lated system [46],... 

The hydrophile of nonionic surfactants is usually a polyoxyethylene chain or consists of polyoxyethylene and polyoxypropylene segments. The length of the hydrophilic chain can be conveniently varied to modify the hydrophile-lipophile balance (HLB) of the surfactant, a property which affects interfacial behavior and the stabilization of emulsions. 

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