Hydrophilic-hydrophobic balance value

The other quantitative criterion is hydrophilic-hydrophobic balance value defined as ... 

Asymmetric Membrane Studies. In light of the results presented in the preceding two sections, plus those found in the literature (21-26,28), the decision was made to commence the asymmetric membrane studies with SPSF-Na(0.A2). The selection of the sodium salt polymer was based on the desire to limit ion exchange in desalination. The selection of D.S. of 0.A2 represents a compromise of hydrophilic/hydrophobic balance and structural stability. The exploration of asymmetric membranes cast from the pol3rmers of other salts and various D.S. values is planned for the future. 

The colloidal stability of polymer dispersion prepared by the emulsion copolymerization of R-(EO)n-MA was observed to increase with increasing EO number in the macromonomer [42, 96]. Thus C12-(EO)9-MA did not produce stable polymer latexes, i.e., the coagulum was observed during polymerization. This monomer, however, was efficient in the emulsion copolymerization with BzMA (see below). The C12-(EO)20-MA, however, appears to have the most suitable hydrophilic-hydrophobic balance to make stable emulsions. The relative reactivity of macromonomer slightly decreases with increasing EO number in macromonomer. The most hydrophilic macromonomer with co-methyl terminal, Cr(EO)39-MA, could not disperse the monomer so that the styrene droplets coexisted during polymerization. The maximum rate of polymerization was observed at low conversions and decreased with increasing conversion. The decrease in the rate may be attributed to the decrease of monomer content in the particles (Table 2). In the Cr(EO)39-MA/St system the macromonomer is soluble in water and styrene is located in the monomer droplets. Under such conditions the polymerization in St monomer droplets may contribute to the increase in r2 values. 

As well as the more common oil in water suspension methods, it is also possible to make stable water in oil suspensions by choosing alternative surfactants with much lower hydrophilic/lipophilic balance values, combined with solvents such as hydrocarbons as the dispersing phase. These can be used to make beaded polymers from water-soluble monomers such as acrylamide. Although little work has been done to date with imprinting in aqueous conditions (using hydrophobic interactions... 

The activity of the catalyst samples for both hydration reactions depends strongly on Nai. For high framework aluminium contents (from 50, corresponding to the parent H-Y, to about 35) the catalyst samples are inactive. This is probably due to the hydrophilic properties of the zeolite s active surface. The catalytic activity increases with the framework dealumination to reach a maximum value at Nm = 22. This increase is likely to be due not only to the increase in the acid strength of the Bronsted sites, but also to the changing in the hydrophilic/hydrophobic balance of the zeolite s active surface. 

I.2.2. Hydrophilic-hydrophobic balance (HHB) of collector molecule It is required that the hydrophobicity of the non-polar group of the collector must overcome the hydrophilicity of the mineral surface and the collector-metal bond. Let (AXr) = (Xg -Xm) represent the hydrophilicity of the bond, and (AXm) = (Xa - Xr) the hydrophilicity of the mineral, where Xa and Xb are the electronegativity of different mineral elements. HHB value of a collector is given by the following equation ... 

As discussed before, the borderline between polysoaps and polyelectrolytes or thickeners is determined by the hydrophilic-hydrophobic balance HLB, as well as by the length and the density of the hydrophobic tails chosen. The longer they are, the lower is the content of hydrophobic tails - the Critical Alkyl Group Content CAC [52, 75] - needed in order to produce polysoap behaviour (cf. Sect. 2.3.2). For poly(2-vinylpyridine) and poly(4-vinylpyridine), about 20% of derivatization with octyl tails and about 10% of derivatization with dodecyl tails are needed as a minimum to obtain the characteristic low viscosities [49, 52, 75, 133, 141, 317] (Fig. 17). Comparable CAC values are obtained for derivatized poly(vinyl-imidazol)s [140] and for poly(allylamine)s [152]. Similarly in anionic copolymers of poly(sodium 2-acrylamido-2-... 

EMSORB Ethoxylated Sorbltan Esters are the hydrophilic counterparts to the hydrophobic EMSORB Sorbltan Fatty Acid Esters. Varying moles of ethylene oxide are added to the Sorbltan Patty Acid Ester to produce these materials. The more ethylene oxide added the more hydrophilic the molecule becomes as seen by its increased Hydrophile-Lipophile balance Value (HLB). 

C for varying periods of time. Clearly the slope of decomposition is reduced as the pH is raised. The stability of hyper-molar urea solution is considerably increased by absorbing the solution into a polysaccharide particle. This particle can then be suspended in a continuous lipid phase with the correct incorporation of surfactants with a hydrophile/lipophile balance value suitable to maintain an aqueous-in lipid, continuous phase. The result of this is a compartmentalized system where the urea is in a more stabilized state and the polysaccharide has been altered in its hydrophobic/lipophilic properties to become what might be termed an ambiphilic matrix. 

The hydrophilic/hydrophobic balance of RTILs is of importance in the evaluation of their impact on the environment and their toxicity. The ionic character of RTILs makes them considerably hydrophilic, unless they carry long alkyl chains that turn them to be hydrophobic. The common measure of this hydrophilic/hydrophobic balance is the logarithm of the 1-octanol/water partition coefficient, logP°w> for dilute solutions of the substance in questimi in the mutually saturated 1-octanol/ water system. The values for RTILs are shown in Table 6.18. The values of logP°w are concentration dependent, and this explains to some extent the discrepancies noted in Table 6.18 between the values reported by different authors ideally the values should pertain to infinite dilution in both phases. 

The resulting products are the most important class of nonionic - surfactants. EO is the major reagent, PO is used to modify the hydrophilic/hydrophobic balance (->HLB value) of the surfactant. 

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... 

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]. 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

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). 

Surfactants have the property of adsorbing strongly on hydrophobic particle surfaces. They consist of a hydrophilic polar head such as -(CH2CH20)n0H, -0S02Na+, -N+(CH3 )2 (CH2 )2 S03 and a hydrophobic tail (i.e., linear or branched hydrocarbon chain). The hydrophobic tail adsorbs on the hydrophobic particle surfaces while the hydrophilic head sticks out toward water. The particles are thus hydrated. Surfactants with a hydrophilic/lipophilic balance (HLB) (see Section 4.2) value close to 7 to 9 are well suited as wetting agents. These surfactants form monolayers on the solid surface. 

Generalizations from the aqueous-solution surface tensions in Table IX are risky, because values are as dependent on the hydrophilic-lipophilic balance (HLB) as on the intrinsic surface activity of the hydrophobe. The data in Table IX are consistent with earlier observations that longer per-fluorinated groups are most effective in producing low surface tensions (in this case CF3(CF2)5-) and that a terminal CF2H- is detrimental. 

Griffin devised the concept of hydrophile-lipophile balance (HLB) and its additivity many years ago for selection of non-ionic emulsifiers and this rather empirical method is still widely used. The enormous literature on the HLB of surfactants has been reviewed by Becher. Each surfactant is allocated an HLB number usually on a scale of 0-20, based on the relative proportions of the hydrophilic and hydrophobic part of a molecule. Water-in-oil emulsions are formed generally from oil-soluble surfactants of low HLB number and oil-in-water emulsions from more hydrophilic surfactants of high HLB number. The method of selection is based on the observation that each type of oil will require an emulsifying agent of a specific HLB number to produce a stable emulsion. Thus, oils are often designated two required HLB numbers, one low and one high, for their emulsification to form water-in-oil and oil-in-water emulsions respectively. A series of emulsifiers and their blends with HLB values close to the required HLB of the oil are then examined to see which one forms the most stable emulsion (c.f. Fig. lA). 

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