Winsor

A beautiful and elegant example of the intricacies of surface science is the formation of transparent, thermodynamically stable microemulsions. Discovered about 50 years ago by Winsor [76] and characterized by Schulman [77, 78], microemulsions display a variety of useful and interesting properties that have generated much interest in the past decade. Early formulations, still under study today, involve the use of a long-chain alcohol as a cosurfactant to stabilize oil droplets 10-50 nm in diameter. Although transparent to the naked eye, microemulsions are readily characterized by a variety of scattering, microscopic, and spectroscopic techniques, described below. 

Shioi A and Flarada M 1996 Model for the geometry of surfactant assemblies in the oil-rich phase of Winsor I microemulsions J. Chem. Eng. Japan 29 95... 

Manna A et al 1997 Synthesis and oharaoterization of hydrophobio, approtioally-dispersible silver nanopartioles in Winsor Type II mioroemulsions Chem. Mater. 9 3032... 

L. Winsor (Bechtel Associates Professional Corp.) Can carbon lay-down be avoided dependably by catalyst formulation ... 

L. Winsor What are the estimated potential advantages of steammoderated methanation over hot or cold gas recycle processes ... 

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]. 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

Fatty alcohol- (or alkyl-)ethoxylates, CoE, are considered to be better candidates for LLE based on their ability to induce rapid phase separation for Winsor II and III systems. (Winsor III systems consist of excess aqueous and organic phases, and a middle phase containing bicontinuous microemulsions.) However, C,E,-type surfactants alone cannot extract biomolecules, presumably because they have no net negative charge, in contrast to sorbitan esters [24,26,30,31]. But, when combined with an additional anionic surfactant such as AOT or sodium benzene dodecyl sulfonate (SDBS), or affinity surfactant, extraction readily occurs [30,31]. The second surfactant must be present beyond a minimum threshold value so that its interfacial concentration is sufficiently large to be seen by... 

According to the colloid scientist Winsor, surfactants are defined as compounds which possess in the same molecule distinct regions of hydrophilic and lipophilic character. For example, in the oleate ion there is an alkyl chain that is basically hydrophobic (lipophilic tail) and a COO" headgroup that is hydrophilic (lipo-phobic). Being amphiphilic in nature, surfactants have the ability to modify the interface between various phases [66]. Their effects on the interface are the result of their ability to orient themselves in accordance with the polarities of the two opposing phases. The polar part can be expected to be oriented towards the more polar (hydrophilic, aqueous) phase, whereas the nonpolar tails should direct towards the nonpolar (lipophilic, oil) phase. 

C-E Report, 1975, C-E Critical Heat Flux Correlation for C-E Fuel Assemblies with Standard Spacer Grids, Part I, Uniform Axial Power Distribution, CENPD-162, Combustion Engineering Co., Winsor, CT. (5)... 

The heavy-end portions (usually called heavy fractions) of bitumen (e.g. asphaltenes, preasphaltenes) can exist both in a random oriented particle aggregate form or in an ordered micelle form, peptized with resin molecules (16.17). In their natural state, asphaltenes exists in an oil-external (Winsor s terminology) or reversed micelle. The polar groups are oriented toward the center, which can be water, silica (or clay), or metals (V, Ni, Fe, etc.). The driving force of the polar groups... 

Knop, M., Siegers, K., Pereira, G., Zachariae, W., Winsor, B., Nasmyth, K., and Schiebel, E. (1999). Epitope tagging of yeast genes using a PCR-based strategy More tags and improved practical routines. Yeast 15, 963—972. 

Figure 12.12 THM GC/MS curves of a Winsor Newton lemon alkyd paint (a) and of an alkyd sample taken from Fontana s work Concetto spaziale (1961) (b). Peak assignments 1, 1,3 dimethoxy 2 propanol 2, 1,2,3 trimethoxy propane 3, 3 methoxy 1,2 propandiol 4, 4 chloro benzenamine 5, 3 methoxy 2,2 bis(methoxymethyl) 1 propanol 6, 3 chloro N methyl benzenamine 7, 3 methoxy 2 methoxymethyl 1 propanol 8, 4 chloro N methyl benzenamine 9, phthalic anhydride 10, 3 chloro 4 methoxy benzenamine 11, suberic acid dimethyl ester 12, dimethyl phthalate 13, azelaic acid dimethyl ester 14, sebacic acid dimethyl ester 15, palmitic acid methyl ester 16, oleic acid methyl ester 17, stearic acid methyl ester 18, 12 hydroxy stearic acid methyl ester 19, 12 methoxy stearic acid methyl ester 20, styrene 21, 2 (2 methoxyethoxy) ethanol 22, 1,1 oxybis(2 methoxy ethane) 23, benzoic acid methyl ester 24, adipic acid dimethyl ester 25, hexadecenoic acid methyl ester 26, dihydroisopimaric acid methyl ester 27, dehydroabietic acid methyl ester 28, 4 epidehydroabietol...

Peterson CL, Laniel MA (2004) Histones and histone modifications. Curr Biol 14, R546-551 Pfaffle P, Gerlach V, Bunzel L, Jackson V (1990) In vitro evidence that transcription-induced stress causes nucleosome dissolution and regeneration. J Biol Chem 265 16830-16840 Poch O, Winsor B (1997) Who s who among the Saccharomyces cerevisiae actin-related proteins ... 

Fontell, K., X-ray Diffraetion by Liquid Crystals—Amphiphilie Systems. In Liquid Crystals and Plastic Crystals (G. Gray and P. Winsor, eds.), Vol. 2, Ellis Horwood, Chiehester, 1974. Luzzati, V., Mustaeehi, H., Skoulios, A., and Husson, F., La structure des colloides d associa-tion. I. Les phases liquide-eristalline des systemes amphiphile-eau, Acta Cryst., 13 660-677 (1960). 

These systems were referred to by Clausse t a (21) as Type U systems. On the other hand, with cofurfactants with chain length Cg to Cy (Figur 3 e-g), the Winsor IV domain is split into two disjointed areas that are separated by a composition zone over which viscous turbid and birifringent media are encountered. This second class of systems was referred as Type S systems (24). It can also be seen that the Winsor IV domain reaches its maximum extension at reducing in size below and above C. Moreover, at C, one observes a small monophasic region near the W apex (probably o/w microemulsion of the Schulman s type) which vanishes as the alcohol chain length is increased to Cg. 

The first of these to be discussed will be the Cohesive Energy Ratio, R concept (20), Using the concept of cohesive energy between molecules, Winsor recognized four structures. 

These are present in an immiscible two-phase system (0 and W denoting oil and water, respectively) containing a third-surfactant component with partial solubility in both bulk phases. Each surfactant molecule has a hydrophilic (denoted by H) and a lipophilic (denoted by L) section. Conceptually then Winsor views all the possible molecular interactions in such a system in terms of their cohesive energy (denoted by C). For such a system, there are then 10 possible cohesive molecular interactions (i.e., 10 unique combinations of the letters 0, W, H, and L). In the ideal case, the lipophile-oil and the hydrophile-water interaction will be the predominant interactions. The relative magnitude (R) of these two interactions... 

The main advantage to the Winsor system is its heuristic feature of treating all cohesive interactions in a two-phase surfactant system. However, to date only the simple form of Equation 22 has been exploited quantitatively (21, 23) as... 

In Table 3 are the values of surface tension for the aqueous LAS homolog solutions. Values of molar volume used are those for the pure LAS homolog independent of water. The justification for this comes from the Winsor R model (20, 21) and work by Scriven and Davis (30) who showed that accurate CED values can be obtained from a statistical mechanical treatment of an interface using only 2 or 3 atomic or molecular layers of that interface. For a surfactant solution, the surfactant will predominate in the interface, hence the choice of pure LAS for the solution molar volumes. 

Hard- ness (ppm) LAS Homo log Cube Root Molar Volume (mole/ cm3)1/3 Surface Tension at. 024% (dynes/ cm) CED Molar At-for LAS traction Solutions Constant 6w for (Hilde- Sulfonate brands) sulf Winsor R Experi- mental Deter- sw Experi- mental Calcu- lated ... 

P. Winsor, "Solvent Properties of Amphiphilic Compounds," Butterworth Sci. Publ., London, 1954. 

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