A. Aserin

A DSC study of water behavior in water-in-oil microemulsions stabilized by sucrose esters and butanol

Abstract Sub-zero temperature differential scanning calorimetry (SZT-DSC) has been applied to a model nonionic water-in-oil microemulsion system based on: sucrose esters/water/1-butanol/ n -alkanes (C 12 –C 16 ). The maximum water solubilization was 40, 56 and 80 wt.% for the systems containing n -dodecane, n -tetradecane and n -hexadecane as the oil phase, respectively. Two types of solubilized water have been detected. The so-called ‘bulk’ (free) water present in the core of the microemulsion and the ‘interfacial’ (bound) water attached at the interface to the surfactant (and/or butanol). The internal distribution of the water within the microemulsions was determined along two dilution lines (with 32 and 43 wt.% of the initial surfactant). It was found that for the n -dodecane system the maximum ‘interfacial’(bound) water is 12 and 14 wt.% along the two dilution lines, respectively. Above this water content a core of ‘bulk’ (free) water is formed. The type of the oil and the butanol interfacial participation strongly affect the water internal distribution. Both the temperature of fusion, T f , of the ‘bulk’ (free) water and of the ‘interfacial’ (bound) water are strongly affected by the butanol and the oil. The nature of the surfactant, its fatty chain length and its HLB also affect the binding capabilities and capacity of water in microemulsion systems. For both n -dodecane and n -hexadecane, 11–13 molecules of water can be bound to the surfactant at the interface.

Sucrose Ester Microemulsions

Abstract 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.

Non-ionic sucrose esters microemulsions for food applications. Part 1. Water solubilization

Abstract Factors affecting water solubilization in four-component nonionic microemulsion systems stabilized by polyol nonionic surfactants (sucrose esters) have been investigated. The effect of changing the chain length of alcohol (used as cosurfactant) and the lipophilic moiety of surfactant have been explored. The maximum water solubilization in the isotropic region (at oil/n-butanol ratio of 1) was 47, 23 and 55 wt.% for sucrose stearate (S-1570), sucrose laurate (L-1695) and sucrose palmitate (P-1570), respectively. Replacing the triglyceride oil (MCT) by dodecane caused a decrease in the water solubilization (40 wt.%) for sucrose stearate with an oil/n-butanol ratio of 1. The empirical BSO (Bansal, Shah, O’Connell) [1] equation which was derived as an empirical condition for maximum water solubilization in microemulsions stabilized by anionic surfactants, in relation to the cosurfactant (alcohol) and oil chain lengths, i.e. NS=NO+NA, where NS, NO, NA are the surfactant chain lengths, oil and alcohol, respectively, was re-examined for this type of surfactants. This study demonstrates that a maximum water solubilization is obtained when the NS=(NO±3)+NA for NS is greater than 14; when NS is less than 14, this equation cannot predict the maximum water solubilization.

A study of the microstructure of four-component sucrose ester microemulsions by SAXS and NMR

Sucrose esters form a class of surfactants with the important properties of being biodegradable, non-toxic and capable of forming temperature-insensitive microemulsions. Such microemulsions would be expected to suit a variety of food-based and pharmaceutical applications; however to date little is known about their structure and stability. In this study, the Winsor IV microemulsion systems composed of sucrose esters (SE)/1-butanol/water and oils such as n-dodecane, n-hexadecane and medium chain triglyceride (MCT), have been investigated using small angle X-ray scattering (SAXS), pulsed gradient spin echo (PGSE) NMR and viscosity measurements. The SAXS results for the sucrose monostearate (S1570) system at SE/MCT/1-butanol=1.5:1.1 clearly indicate that the periodicity d increases with increase in water content and is not sensitive to the nature of the oil. From the amphiphilicity factor, fa, and the correlation length, ξ, one can conclude that the n-dodecane-based microemulsion system is the most ordered. Microstructure investigation by PGSE NMR gives evidence of structural changes as the water content in the system increases. The oil self-diffusion remains unchanged when MCT serves as the oil phase. However, when the oil is paraffinic in nature (n-dodecane and n-hexadecane) the self-diffusion coefficient indicates participation of the oil molecules at the interface. Surfactant self-diffusion is only weakly affected by the water content. The shorter chain oils (n-dodecane and MCT) solubilize a maximum of 40 and 47 wt.% of water and cannot invert, while the long chain paraffinic (n-hexadecane-based system) inverts into an O/W microemulsion. The viscosity of these microemulsions decreases with increasing water content. The absence of a yield stress in any of the samples studied, together with the linearity of the flow curves, is evidence that there are no relaxation processes in these microemulsions which show a non-Newtonian flow behavior.

Polyglycerol esters: Optimization and techno-economic evaluation

Optimization of the two-step reaction for preparation of polygly-cerol esters of fatty acids from the industrial point of view has been studied. Parameters such as nature of the alkaline catalyst, tempera-ture and time of the reaction have been examined. It was found that the polymerization process needs 260–280 C in the presence of inert gas and 2.5 mol % of NaOH as catalyst. The esterification can be accomplished in the absence of additional catalyst and temperatures as low as 230 C. A simulation model of a chemical plant has been used for evaluation of cost of the production of such emulsifiers.

Sub-zero temperature behaviour of non-ionic microemulsions in the presence of propylene glycol by DSC

The five-component system is quite unique since it allows formation of reverse micelles with hydrophilic ethoxylated alcohol in the presence of ethanol and it facilitates dilution by water/propylene glycol (1,2-propanediol, PG) aqueous phase, all the way from a water-in-oil (W/O) microemulsion via a bicontinuous phase to an oil-in-water (O/W) microemulsion.The surfactant/alcohol/PG can strongly bound water in the inner phase so that it freezes below −10°C and acts in part as ‘bound’ water and in part as ‘non-freezable’ water. Upon dilution to >30 mass% aqueous phase (water/PG at constant mass ratio of 1/1) the system becomes bicontinuous and the aqueous layers are composed again from bound water. Even after complete inversion to O/W microemulsions the water in the continuous phase is strongly interacting with the PG/surfactant and remains bound or non-freezable. Water/PG/ethanol have a strong effect on the head groups (freezing below -10°C) and also on the hydrophobic tails (recrystallizing and melting) at lower temperature when dilution exceeds 45 mass% water/PG (1/1).No free water was detected neither in the W/O microemulsions inner droplet domains nor when the microemulsion was either bicontinuous or when it was inversed to O/W. Continuous phase of resulting O/W microemulsion apparently is based on water/PG at a mass ratio of 1/1.

Low viscosity reversed hexagonal mesophases induced by hydrophilic additives.

This study reports on the formation of a low viscosity H(II) mesophase at room temperature upon addition of Transcutol (diethylene glycol mono ethyl ether) or ethanol to the ternary mixture of GMO (glycerol monooleate)/TAG (tricaprylin)/water. The microstructure and bulk properties were characterized in comparison with those of the low viscosity HII mesophase formed in the ternary GMO/TAG/water mixture at elevated temperatures (35-40 degrees C). We characterized the role of Transcutol or ethanol as inducers of disorder and surfactant mobility. The techniques used were rheology, differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS and SAXS, respectively), NMR (self-diffusion and (2)H NMR), and Fourier transform infrared (FTIR) spectroscopies. The incorporation of either Transcutol or ethanol induced the formation of less ordered HII mesophases with smaller domain sizes and lattice parameters at room temperature (up to 30 degrees C), similar to those found for the GMO/TAG/water mixture at more elevated temperatures (35-40 degrees C). On the basis of our measurements, we suggest that Transcutol or ethanol causes dehydration of the GMO headgroups and enhances the mobility of the GMO chains. As a result, these two small molecules, which compete for water with the GMO polar headgroups, may increase the curvature of the cylindrical micelles and also perhaps reduce their length. This results in the formation of fluid H(II) structures at room temperature (up to 30 degrees C). It is possible that these phases are a prelude to the H(II)-L(2) transformation, which takes place above 35 degrees C.

Analysis of sorbitan fatty acid esters by HPLC

Sorbitan esters of several fatty acids have been analyzed by high pressure liquid chromatography (HPLC) using an RP-18 column. No derivatization was necessary. Mono-, di- and trisorbitan esters of palmitic, stearic, oleic, isostearic and sesquioleic acid have been separated using isopropanol/water as the elution mixture.

HPLC analysis of nonionic surfactants. Part IV. Polyoxyethylene fatty alcohols

A high performance liquid chromatographic technique (HPLC) was applied to analyze nonionic surfactants of ethylene oxide (EO) adducts. Pattern analyses of EO adducts (ethers), with 2, 10 and 20 average EO units, were carried out using a Lichrosorb SI-60 (10 μm) column (4.6 mm inner dimension (id)×25 cm) under the following conditions: mobile phase-mixture of isopropanol, methanol and n-hexane (gradient): temperature of 50 C: UV detector at 220 nm. No derivatization of the compounds was needed. An improved baseline, in spite of gradient elution, was achieved by adding negligible amounts of anthracene to the eluents. Brominated ethoxylated alcohols, resulting from the addition of bromine to the hydrophobic chain of the ethoxylated fatty alcohol, did not require any changes in the elution conditions.

Maillard Reaction between Leucine and Glucose in O/W Microemulsion Media in Comparison to Aqueous Solution

The Maillard reaction is controlled by temperature, pH, reactant nature (sugars and amino acids), and water activity. We carried out reactions between glucose and leucine in U‐type nonionic microemulsions to obtain regioselectivity and control reaction rates. Reactants were oriented at the interface and water activity was adjusted using blends of surfactant and propylene glycol (PG). U‐type microemulsions, previously studied by us, served as microreactors for the Maillard reaction. The reactions in the microemulsion media were slower than those carried out in aqueous solution and formed unique aroma compounds. Reaction rates increased when using systems richer in water, as the water activity was enhanced. The surfactant plays a key role in determining water activity and reagent reactivity in all the microemulsions. The presence of PG slows the reaction, mainly when it resides at the interface, facilitating the formation of a bicontinuous structure. Phase transitions within the U‐type microemulsions were determined by viscosity and SD‐NMR and were correlated to the interfacial presence of the reactants and their reactivity.