Hydrophobic “tail,” of surfactant

In the case of precipitated silica, great endothermic contribution due to the displacement of interfacial water by the hydrophobic tails of surfactants may obscure the evaluation of the effect of the chain length on the enthalpy of displacement. As raising the temperature reduced this contribution to a great extent (see Fig.5b), the appropriate calorimetric experiments were carried out at 308 K. The results are presented in Fig.lO. 

In addition to the adsorption process, in which the molecules reach the interface depending on their structure and relationship with the solvents, amphiphilic molecules show the tendency to organize and coordinate themselves into ordered sttuctures in water or solvent including the formation of aggregates such as micelles, liquid crystals (LCs), or bilayers. Such self-assembly phenomena can be described when the hydrophobic tails of surfactant molecules form a cluster to produce small aggregates, such as micelles, or large layered structures such as bilayers that are similar to a cell wall. ... 

Finally, we tike to mention that after having analyzed the compositions and the structures of the complexes, we can calculate the size and the aggregation number of the micettes packed inside the complexes. The detail calculation procedure can be found elsewhere. Both the aggregation number and the size of micettes packed in the complexes dqrend on the charge density of poiyelectrolyte chains, the flexibility of poiyelectrolyte backbone chains, and the hydrophobic tail length of surfactants. Nevertheless, foe size and the aggregation number of foe micettes formed inside the... 

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]. 

Oxyethylated surfactants The multiple condensation of ethylene oxide with a hydrophobe that contains accessible hydrogen atoms yields a polyethylene-oxide with an attached hydrophobic tail group. Polyethyleneoxide surfactants constitute the major portion of nonionic surfactants. The ability to control the... 

FIG. 10 The effect on emulsion type of changing the hydrophobic tail length of n-alkyl carboxylate surfactants. The question mark domain corresponds to the emulsion breaking region where emulsion type was found to be uncertain. C9, Cll, C13, and C15 stand for m = 9, 11, 13, and 15 in the above surfactant chemical structure (From Ref. 152.)... 

The contribution of amino acids to the overall hydrophobicity of the protein is limited, compared to the contribution of a hydrophobic tail in classic surfactants, such as ethoxylated fatty acids. Therefore it can be expected that incorporation of long hydrocarbon chains will affect significantly the surface activity of the protein, as will be described in the following sections. 

The formation of an aggregate yields an interface between the hydrophobic core consisting of surfactant tails and bulk water. The free energy of formation of this interface was considered as a product of the surface area in contact with water and the macroscopic interfacial tension of this interface... 

The hydrophobic (tail) part of the surfactant is typically a single alkyl chain in small-molecule surfactants, while polymeric surfactants have hydrophobic regions composed of less soluble polymers. Thus triblock copolymers of the type poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO PO ,EO ) form micelles with poly(propylene oxide) in the hydrophobic core, and the poly(ethylene oxide) strands on the outside of the micelle. These triblock copolymers, particularly the... 

Fluorinated surfactants have unique properties that make them highly suitable for many industrial processes,use in consumer products. and biomedicaF and research applications such as novel material synthesis applications. Several unique characteristics of the fluorine atom contribute to the properties of surfactants with a highly fluorinated hydrophobic tail (or fluorinated surfactants... 

The foregoing is intended to provide some insight into the potential research and application opportunities of PBS in the food sector. The surface activity of food proteins is regarded as the most important property, for it influences the quality and utility of emulsions and foams. Accordingly, enhancement of the surface activity of food proteins is very important and can be achieved by hydrophobic modification. The contribution of amino acids or peptides per se to the overall hydrophobicity of food proteins is limited, compared to the contribution of a hydrophobic tail in classic surfactants, such as ethoxylated fatty acids [78]. Therefore, it can be expected that the incorporation of long hydrocarbon chains will affect significantly the surface activity of proteins. 

Yan and Texter have synthesized amphiphihe ILs (IL-S) that consists of an imidazolium cation polar group and a hydrophobic tail including polymerizable surfactant ILs (Scheme 13,3) [87]. Microemulsions were formulated with IL-S/ methyl methacrylate (MMA)/water in highly diluted systems where oil-in-water type aggregates are formed. 

Figure C2.3.14. Isolated surfactant modes of adsorjDtion at liquid-solid interfaces for a surfactant having a distinct headgroup and hydrophobic portion (dodecyltrimetlrylammonium cation) (a), (b) headgroup specific interaction (c), (d) hydrophobic tail interaction, (e),(f) headgroup and tail interactions.

Amphiphilic molecules (surfactants) are composed of two different parts hydrophobic tail and hydrophilic head [1 ]. Due to their chemical structure they self-assemble into internal surfaces in water solutions or in mixtures of oil and water, where the tails are separated from the water solvent. These surfaces can form closed spherical or cylindrical micelles or bicontinuous phases [3,5]. In the latter case a single surface extends over the volume of the system and divides it into separated and mutually interwoven subvolumes. 

As esters of sulfuric acid, the hydrophilic group of alcohol sulfates and alcohol ether sulfates is the sulfate ion, which is linked to the hydrophobic tail through a C-O-S bond. This bond gives the molecule a relative instability as this linkage is prone to hydrolysis in acidic media. This establishes a basic difference from other key anionic surfactants such as alkyl and alkylbenzene-sulfonates, which have a C-S bond, completely stable in all normal conditions of use. The chemical structure of these sulfate molecules partially limits their conditions of use and their application areas but nevertheless they are found undoubtedly in the widest range of application types among anionic surfactants. 

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