Sub-zero temperature behavior of water in non-ionic microemulsions

Sub-zero temperature DSC measurements were conducted to evaluate the behavior of water in non-ionic microemulsions. Two surfactant systems were studied. The first, based on ethoxylated fatty alcohol, octaethylene glycol monon-dodecylether [hereafter referred to as C₁₂(EO)₈] and also containing water, pentanol and dodecane at a fixed weight ratio of 1:1. The second system, based on oligomeric ethoxylated siloxanes, water and dodecanol as oil phase. In both systems it was found that in up to 30 wt.% of the total water content, all water molecules solubilize in the amphiphilic phase and are bound to the ethylene oxide (hereafter referred to as EO) head-groups. No free water exists in the surfactant aggregates’ core. Up to three molecules of water are bound to each EO group. In the first system, the behavior changes significantly upon adding more water. The added pentanol allows further swelling and the water penetrates into the amphiphile structures and forms a reservoir of free water. Structures are deformed and grow from elongated channels (up to 15–20 wt.% water), via illdefined (one-dimensional growth) local lamellar structures (up to ca. 60 wt.% water) to spherical normal, O/W micelles (at ≥85 wt.% water). In contrast, the oligomeric systems, due to geometrical restrictions of the amphiphiles and the nature of their curvature that prevents inversion, cannot further solubilize water in the surfactant aggregates’ core, causing phase separation to occur. Part of the results presented in this paper were included in S. E.’s doctoral thesis in Applied Chemistry at The Hebrew University of Jerusalem, Israel.     

Enthalpies of solution in sodium octanoate + water + alcohol mixtures

Enthalpies of solution of sodium octanoate in water, 1-propanol and aqueous mixtures of 1-propanol, 1-butanol, 1-pentanol and 1-hexanol, and of the alcohols in aqueous solutions of sodium octanoate at various concentrations were determined calorimetrically at 35 °C. MostH(soln) values are exothermic and strongly dependent on the solute concentration. The main energetic factor governing the process of dissolution of the surfactant is associated with changes in the water structure caused by the presence of alcohol. That governing the process of the alcohol dissolution in surfactant solutions is due to the effect alcohols have on the CMC of the octanoate. There is no indication of the alcohol being either solubilized in the interior of the aqueous micelle, or becoming part of the micellar film.The solubility at 35 °C of sodium octanoate in water, 1-propanol and their mixtures has also been determined.     

Five-component food-grade microemulsions: structural characterization by SANS

In this paper we present the structural characterization of a five-component food-grade microemulsion containing Tween 80, R(+)-limonene, ethanol, glycerol, and water. Our main approach to investigating the microstructure of dense microemulsions, and how it can be influenced by the various components, was to employ small-angle neutron scattering and the new evaluation technique for dense, interacting systems, the Generalized Indirect Fourier Transformation. We started our investigation with the impact of glycerol and ethanol on Tween 80 micelles in water. We found that glycerol increases the aggregation number and withdraws the hydrating agents from the headgroup region of the surfactant, resulting in a higher packing density of molecules in a micelle at slightly increasing size. The same trend holds when the micelles are oil swollen and/or ethanol is present. Ethanol, on the other hand, redistributes mainly between water and the interface-headgroup region of the surfactant. Part of it replaces surfactant molecules in the micelles, which increases the available interface and results in a higher number of micelles with shrinking size. The same trend holds when the micelles are oil swollen and/or glycerol is present in the aqueous phase. We also investigated samples along the dilution of a mixture of surfactant and oil phase (R(+)-limonene and ethanol), which can be diluted with aqueous phase (mixture of water and glycerol) without the occurrence of phase separation. In some samples of this dilution most probably bicontinuous structures are present. To elucidate this point, we also employed dynamic light scattering, viscosity, and conductivity measurements.     

Water Solubilization in Nonionic Microemulsions Stabilized by Grafted Siliconic Emulsifiers

Microemulsions containing octanol, decanol, or dodecanol as the oil phase and oligomeric, grafted nonionic amphiphiles based on ethoxylated polymethylsiloxanes (Silwets) have been studied. It was demonstrated that significant amounts of water can be solubilized only when the hydrophobic siliconic backbone is very short (trimers). The water solubilization was evaluated using SAXS, DSC, and conductivity measurements. It was found that up to 40 wt% of water can be solubilized in dodecanol and Silwet L-7607 (MW 1000 and 75 wt% ethylene oxide (EO)). Surprisingly, no free water was detected in the aggregate core. All the solubilized water was confined in the vicinity of the interphasal region and froze at -10 degrees C and below. Up to three molecules of water can be associated with each EO headgroup. Based on SAXS measurements, the structural units of the microemulsions were interpreted to be lamellar-like, a form previously found for the related monomeric microemulsions. Copyright 2001 Academic Press.     

Transitions induced by solubilized fat into reverse hexagonal mesophases

Lyotropic liquid crystals of glycerol monooleate (GMO) and water binary mixtures have been extensively studied and their resemblance to human membranes has intrigued many scientists. Biological systems as well as food mixtures are composed of lipids and fat components including triacylglycerols (TAGs, triglycerides) that can affect the nature of the assembly of the mesophase. The present study examines the effect of TAGs of different chain lengths (C(2)-C(18)) at various water/GMO compositions, on phase transitions from lamellar or cubic to reverse hexagonal (L(alpha)-H(II) and Q-H(II)). The ability of the triglycerides to promote the formation of an H(II) mesophase is chain length-dependent. It was found that TAG molecules with very short acyl chains (triacetin) can hydrate the head groups of the lipid and do not affect the critical packing parameter (CPP) of the amphiphile; therefore, they do not affect the self-assembly of the GMO in water, and the mesophase remains lamellar or cubic. However, TAGs with medium chain fatty acids will solvate the tails of the lipid, and will affect the CPP of the GMO, and transform the lamellar or cubic phases into hexagonal mesophase. TAGs with long chain fatty acids are very bulky, not very miscible with the GMO, and therefore, kinetically are very slow to solvate the lipid tails of the amphiphile and are difficult to accommodate into the lipophilic parts of the GMO. Their effect on the transitions from a lamellar or cubic phase to hexagonal is detected only after months of equilibration. In order to enhance the effect of the TAG on the phase transitions in the GMO/triglyceride/water systems, temperature and electrolytes effects were examined. In the presence of short and medium chain triglycerides, increasing temperature caused a transition from lamellar or hexagonal to L(2) phase (highest CPP value). However, in the presence of long chain TAGs, increasing temperature to ca. 40 degrees C caused a formation of H(II) mesophase. In addition, it was found that in tricaprylin/GMO/water systems, the increase in temperature caused a decrease in the lattice parameter. The effect of NaCl on the H(II) mesophase revealed interesting results. At low concentration of tricaprylin (5 wt%), the addition of only 0.1 wt% of NaCl was sufficient to cause the formation of well-defined H(II) mesophase, while further addition of electrolyte increased the hexagonal lattice parameters. At higher TAGs concentrations (10 wt%), addition of electrolyte resulted in the formation of H(II) with modifications of the lattice parameter. All the examined effects were more pronounced with increasing water content.     

Analysis of Nonionic Surfactants by High Performance Liquid Chromatography

Abstract

This review discusses the principles of immobilized metal ion affinity chromatography (IMAC) and its applications to protein separations. IMAC functions by binding the accessible electron-donating pendant groups of a protein - such as histidine, cysteine, and tryptophan - to a metal ion which is held by a chelating group covalently attached on a stationary support. A common chelating group is iminodiacetate. The ions commonly used are of borderline or soft metals, such as Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺. Protein retention in IMAC depends on the number and type of pendant groups which can interact with the metal. The interaction is affected by a variety of independent variables such as pH, temperature, solvent type, salt type, salt concentration, nature of immobilized metal and chelate, ligand density, and protein size. Proteins are usually eluted by a decreasing pH gradient or by an increasing gradient of a competitive agent, such as imidazole, in a buffer. There are still several unresolved issues in IMAC. The exact structures of protein-immobilized metal complexes need to be known so that retention behavior of proteins can be fully understood and sorbent structures can be optimized. Engineering parameters, such as adsorption/desorption rate constants, sorbent capacities, and intraparticle diffusivities, need to be developed for most protein systems. Engineering analysis and quantitative understanding are also needed so that IMAC can be used efficiently for large scale protein separations.     

Protein-Polysaccharide Interactions for Stabilization of Food Emulsions

Proteins, polysaccharides and their blends, as examples of natural biopolymers, are surface active materials. Biopolymers may be considered as amphiphilic macromolecules that play an essential role in stabilizing food formulations (foams, emulsions and dispersions). Under specific conditions (such as protein-to-polysaccharide ratio, pH, ionic strength, temperature, mixing processing), it has been stated that proteins and polysaccharides form hybrids (complexes) with enhanced functional properties in comparison to the proteins and polysaccharides alone. Different protein-polysaccharide pairs are reviewed with particular attention to the emulsification capability of their mixtures. In the case of uncomplexed blends of biopolymers, competitive adsorption onto hydrophobic surfaces is generally reported. Conversely, electrostatic complexation between oppositely charged proteins and polysaccharides allows better anchoring of the new-formed macro-molecular amphiphile onto oil-water interfaces. Moreover, improved thermal stability and increased resistance to external treatment (high pressure) involved in food processing are obtained. This review presents basic and applied knowledge on protein-polysaccharide interactions in aqueous medium and at the oil-water interface in food emulsion systems. Electrostatic interactions and thermodynamic incompatibility in mixed biopolymer solutions are correlated to the functional properties (rheology, surface hydrophobiciry, emulsification power) of these interesting blends. Basic and industrial selected systems of different families of hydrocolloids (as gum Arabic, galactomannans, pectins) and protein (caseins, whey, soya, gelatin) mixtures are reviewed.     

Constraining the variation of fundamental constants using 18 cm OH lines

We describe a new technique to estimate variations in the fundamental constants using 18 cm OH absorption lines, with the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition, it is possible to simultaneously measure changes in alpha, g(p), and y identical with m(e)/m(p). We use the 1665 and 1667 MHz line redshifts in conjunction with those of HI 21 cm and mm-wave molecular absorption in a gravitational lens at z approximately 0.68 to constrain changes in the three parameters over the redshift range 0相似文献   

Sucrose ester microemulsions

Sucrose esters are biodegradable surfactants that can be manufactured in various hydrophilic-lipophilic properties using different fatty acids varying in their lipophilic chain length. These surfactants are used in different industries including pharmaceutical, food processing, detergents, agricultural and others. Few number of works had been done using sucrose esters in microemulsions. In this review we tried to introduce the relevant works that enlighten the behavior of sucrose esters in phase diagrams prepared using different oils and medium chain alcohols.

We hope that this review article can be an aid to those researchers interested in microemulsions based on sucrose esters and their applications.