Ethoxylated Sorbitan Esters Research Articles

Solubilization Rates of n-Alkanes in Micellar Solutions of Nonionic Surfactants

Accurate prediction of surfactant-enhanced recovery of organic contaminants in soils requires estimates of micellar solubilization rates. This study examines the influence of surfactant properties on the rates of solubilization of octane, decane, and dodecane in micellar solutions of a homologous series of purified dodecyl alcohol ethoxylates and two commercial surfactants, an ethoxylated linear alcohol (Witconol SN-120) and an ethoxylated sorbitan ester (Witconol 2722). A batch mixing technique was employed to investigate these solubilization rates. For all surfactants studied, solubilization rates were found to increase with a decrease in solute chain length. For the purified surfactants, solubilization rates also increased with ethoxylate chain length. Batch concentration data were fit with a linear driving force mass transfer model. Effective mass transfer coefficients determined from these data ranged over more than one order-of-magnitude for the systems examined. Correlations developed for the effective mass transfer coefficients exhibit a dependence on the solute micelle-water partition coefficient, solute molar volume, and surfactant hydrophile-lipophile balance or ethoxylate chain length. Although the measured coefficients are specific for this experimental system, the results demonstrate the importance of employing organic and surfactant properties in the estimation of solubilization rates.

Assembly of Mesoporous Silica Molecular Sieves Based on Nonionic Ethoxylated Sorbitan Esters as Structure Directors

A new family of mesoporous silica molecular sieves with micelle-templated structures (MTS) has been synthesized using nonionic ethoxylated sorbitan esters, namely, Tween-20, -40, -60, or -80, as structure-directing agents. These MTS materials possess a wormhole-like framework typical of MSU-X mesostructures, with intraparticle (framework) pore sizes in the 3.0−4.0 nm range. Unlike previously reported MSU-X silicas, these new derivatives form monodispersed small particles in the 30−60 nm range, depending on the nature of the surfactant, and exhibit substantial interparticle (textural) porosity in the 9−20 nm range. The sorbitan surfactants are nontoxic, biodegradable, and biocompatible when solvent free, making them attractive structure directors for the synthesis of mesoporous materials. The combination of complementary framework and textural pore distributions should be advantageous in the use of the mesostructures as heterogeneous catalysts, particularly for reactions that are normally diffusion limited.

Competitive adsorption in O/W emulsions stabilized by the new Portulaca oleracea hydrocolloid and nonionic emulsifiers

A new water-soluble anionic, low-molecular weight polysaccharide (gum) with surface, interfacial and emulsification properties was extracted from leaves of the legume Portulaca oleracea (termed by us POG). Vegetable oil-in-water emulsions with small droplets (2–5 μm), stable to flocculation and coalescence (for a few months) can be formed in the presence of 0.1–0.8 wt% POG. The gum adsorbs onto the oil–water interface. The nature of this adsorption was tested by evaluating the competitive adsorption of Tweens (ethoxylated sorbitan esters) and the POG in oil-in-water emulsions. It was demonstrated that Tweens form weak associates with the POG at the interface at certain emulsifier/gum binary mixtures, but any excess concentrations of the Tween will cause a gradual displacement of the gum from the interface. The POG and/or the gum–Tween associates (complex) have weak anchoring capabilities at the interface.

Effect of food emulsifiers on polymorphic transitions of cocoa butter

AbstractThe polymorphic behavior of cocoa butter in the presence of several food emulsifiers serving as crystal structure modifiers was investigated. Emphasis was placed on transitions among the relatively stable forms IV, V and VI, which are significant for a confectionery industry.As known from industry work, within the series of sorbitan esters and ethoxylated sorbitan esters, the solid emulsifiers were the most efficient in retarding transition of V form into VI modification. Blends of sorbitan monostearate (Span 60), ethoxylated sorbitan monostearate (Tween 60) and Span 60‐Tween 65 used in the present study were particularly effective. Surprisingly, it was found that some combinations of emulsifiers accelerate the transition of form IV into form V. Transition of form V into form VI occurs via the solid state, and other transitions are known to take place via the liquid phase. Emulsifier was found to increase liquid fraction of the fat prior to its transition. Mechanistic considerations concerning these transitions are suggested.

Transparent macroemulsions for cosmetic applications

Synopsis This study proposes a method for preparation of transparent emulsions for cosmetic applications. The continuous phase in oil-in-water emulsions consisted of both water and several polyols in order to equalize the refractive indices of the two phases. Sorbitol, glycerol and mannitol were the main polyols used in the adequate concentration and isopropyl myristate was the oil phase. Stabilities of a few days in 60 degrees C incubation and a few months on the shelf were obtained. Combinations of triethanolamine oleate together with sorbitan esters and ethoxylated sorbitan esters were found to improve the emulsion stability. The optimal water concentration was checked by spectrophotometer measurements at 660 nm in order to achieve best transparency. In conclusion, it was demonstrated that relatively stable transparent macroemulsions can be prepared by equalizing the refractive indices of the two phases composing the emulsion.

Effect of food emulsifiers on crystal structure and habit of stearic acid

AbstractSeveral food emulsifiers have been found to serve as crystal structure modifiers for stearic acid crystallized from various organic solvents. Stearic acid that usually precipitates under appropriate crystallization conditions as the B‐ form is converted into the C‐ form when 1‐ 5% of sorbitan esters or ethoxylated sorbitan esters of fatty acids are present in the solution. Other emulsifiers such as polyglycerol esters, bdsubstituted monoglycerides and sucrose esters of fatty acids consisting of bulky hydrophilic groups are also effective emulsifiers in preserving the C‐ form of the crystallized stearic acid. The active emulsifiers modify the external crystal habit of stearic acid. Mass spectrograph analysis indicates that sorbitan monostearate (Span 60) is precipitated with the stearic acid.