Hydrophilic surfactants

The contemporaneous presence of different solubilizates sometimes involves competition for the micellar binding sites [31], For instance, from an analysis of the heats of solution of benzene and water in solutions of reversed micelles of tehaethylene glycol dodecyl ether in decane, a competition between water and benzene for the surfactant hydrophilic groups was shown [32],... 

In the absence of alcohol the salinity/alkane sensitivity will be dominated by the nature of the surfactant hydrophile. A linear response was observed between optimal salinity and alkane chain length for the ICI NP6 surfactant with a recorded coefficient of ds /d EACN = 17.Sgdm "3/1 EACN. This high salt tolerance was expected for nonionics and can reflect an... 

The adsorption of mixed surfactants at the air—water interface (monolayer formation) is mechanistically very similar to mixed micelle formation. The mixed monolayer is oriented so that the surfactant hydrophilic groups are adjacent to each other. The hydrophobic groups are removed from the aqueous environment and are in contact with other hydrophobic groups or air. Therefore, the forces tending to cause monolayers to form are similar to those causing micelles to form and the thermodynamics and interactions between surfactants are similar in the two aggregation processes. 

Variations in the relative polarity or nonpolarity of surfactants (hydrophilic or hydrophobic) signiLcantly inLuence its interfacial behavior. A measure of this parameter is useful to classify surfactants. An HLB number is a direct expression of the hydrophilic and hydrophobic character of surfactants and is a useful means for surfactant classiLcation. HLB numbers for surfactants may be either calculated using the following empirical equation ... 

A micelle that is formed in a non-aqueous medium, thus having the surfactants hydrophilic groups oriented inward away from the surrounding medium. 

In the case of nonionic surfactants, hydrophilic groups orient in the water phase and lipophilic groups orient in the oil or solid phase. 

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. 

From an interfacial energy point of view the main difference between liquid siloxanes and siloxane surfactants in aqueous solution consists in the enhanced orientation of the latter at interfaces. The surfactants hydrophilic moiety is oriented to the water phase, the hydrophobic part to the air (at the liquid/vapour interface) or to the condensed perfluorinated matter (at the solid/liquid interface). 

The conclusions drawn on the basis of the dielectric loss analysis of liquid samples, support the interpretation that a very gradual confluence of the different types of dispersions takes place.Such an interpretation could explain the instauration of polydispersed samples in terms of the coexistence, at equilibrium, first, of micellar aggregates with w/o microemulsion droplets and, successively, of a microemulsion with l-I O-per hydrophilic group monolayer, in equilibrium with a hydrated type of microemulsion (U-water molecule per polar head of the surfactant hydrophilic groups monolayer). The latter interpretation is in accordance with Steinbach and Sucker findings that the two types of structures ( 1-HpO and U-HgO molecule), may coexist at equilibrium (23.). 

Amphiphiles Increase in molecular weight (or branching) of surfactant-hydrophobic part Decrease in polarity of surfactant-hydrophilic part Increase in long-chain alcohol concentration Decrease in short-chain alcohol concentration... 

Giles (Unilever) Cationic surfactant hydrophilically substituted cationic surfactant lipid An anionic surfactant-free formula providing acceptable cleaning and lathering give wet slippy feel to hair... 

EON is the average number of oxyethylene groups in the surfactant hydrophilic group,... 

The transition from non-adsorbing to adsorbing polymers can be achieved simply by changing the surfactant and thus increasing the attraction between polymer and surfactant. Hydrophilic polymers in w/o-droplet microemulsions lead to polymers incorporated in the droplets (Scheme 4.5). Attractive interactions lead to adsorption at the inside of the surfactant film. With increasing chain length confinement effects eventually occur (Scheme 4.6). In this case, the polymer is incorporated in more droplets and the droplets form clusters. Polymers adsorbing on the outside can also lead to droplet clusters. 

In emulsions, amine hydrochloride constitutes the aqueous phase and acrylic ester the organic phase. Cetyltrimethylammonium bromide (CTAB) or span/twin (S/T)-type surfactants are used for emulsion polymerization. Solid dispersants such as talc and colloidal silica are often used to stabilize emulsions which are difficult to stabilize with usual surfactants. Hydrophilic colloidal silica (Aerosil 200) drastically increases the stability of some emulsions provided high amounts (up to 10%) of Aerosil are used. Random copolymers containing 10% hydroxyl groups can be used as polymeric dispersants for preparing w/o emulsions. 

This commentary on the current status of research on heats of immersion begins where our review written in 1958 concludes [6]. The classification of heats of immersion of solids into liquids as a function of precoverage is expanded to include two new types of curves. Several difficulties in heat of immersion research are discussed. Then, current applications of heats of immersion to determine the average polarity of solid surfaces, heterogeneities on solid surfaces, wetting by surfactants, hydrophilicity of solid surfaces, and thermodynamics of the specific interaction of molecules from solution onto solid surfaces are described. 

Applications of the heat of immersion technique to determinations of polarity of surfaces, site heterogeneities, wetting of surfactants, hydrophilicity, and the interaction of specific groups from solution with solids are on the increase. The technique is certain to provide new and valuable information about the solid-liquid interface in the near future. 

Table 2 lists the characteristic parameter EPACNUS selected ionic surfactants. EPACNUS stands for extrapolated preferred alkane carbon number at unit salinity and no alcohol. It is the ACN value fround from equation (8) when In 5 = 0, f A) = 0 and AT= 0, and it is this characteristic of the surfactant. The EPACNUS parameter allows us to compare surfactant hydrophilicity against the ACN scale, which has exactly the same meaning in all correlations, whether for ionic or nonionic systems. The lower the value of EPACNUS, the higher the hydrophilicity of the surfactant. 

Micelles are colloidal aggregates that form above some concentration, the so-called critical micelle concentration (CMC), according to the pattern shown in Fig. I. In a normal micellar aggregate (left), (he surfactant hydrhilic groups are in contact with the aqueous solvent, while the hydrt hobic "tails are located in the micelle core away from the aqueous environment—a favorable situation from an energetic point of view. Inverse micelles (right) are similar in structure but this time the solvent is an oil phase and the surfactant hydrophilic groups arc located inside (3). 

The CER concept, applied to the cosurfactant properties of the monomer, explains the high values of HLBopt observed experimentally. Indeed, incorporating water-soluble monomers into microemulsions improves the chemical match between the aqueous phase and the surfactant hydrophilic entities. As an... 

The templated highly porous titania, bulk and film, were prepared by two methods Mixing and Immersion. Templating materials, surfactants, hydrophilic- and hydrophobic polymers were incorporated into wet gels before drying by these methods (Figure 7.1). 

Figure 10 Vaiiaiion of the emulsion conductivity along two formulation scan.. Saliniit. scan (left) and surfactant hydrophilicity scan (right). (After Ref. (i6).

The enthalpy values associated with the water endotherm allow evaluation of the free water fraction (i.e., melting at 273 K) as well as of the amount of water bound to the surfactant hydrophilic groups. The latter information results Irom the difference between the a priori known water content of the sample, Irom which the expected enthalpy value (A// ) can be estimated, and the amount of water that was foimd to melt at 273 K. The latter is obtained from the measured enthalpy (A// ) value associated with the experimentally recorded DSC peak. Worked examples are given at the end of the next paragraph. 

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