Oil-in-water microemulsions stabilized by 3-( N , N - dimethylalkylammonio)propanesulfonate surfactants of varying alkyl chain length: Solubilisation of testos-terone propionate (original) (raw)
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Journal of Colloid and Interface Science, 1986
Phase diagrams have been determined showing the extent of the inverse micellar or microemulsion region for systems consisting of water-surfactant-cosurfactant or water-surfactant-hydrocarbon cosurfactant mixture with three surfactants and four cosurfactants. The surfactants are sodium dodecyl sulfate, sodium laurate, and tetradecyltrimethylammonium bromide while the cosurfactants are pentanol, hexanol, pentylamine, and hexylamine. Hexylamine is found to be a very effective cosurfactant giving rise to very good water solubilizing capacity at extremely low surfactant concentrations and very low eosurfactant levels at rather high initial hydrocarbon levels.
Journal of Colloid and Interface Science, 2012
The present study is focused on the evaluation of the interfacial composition, thermodynamic properties, and structural parameters of water-in-oil mixed surfactant microemulsions [(cetylpyridinium chloride, CPC + polyoxyethylene (20) cetyl ether, Brij-58 or polyoxyethylene (20) stearyl ether, Brij-78)/ 1-pentanol/n-heptane, or n-decane] under various physicochemical environments by the Schulman method of cosurfactant titration of the oil/water interface. The estimation of the number of moles of 1-pentanol at the interface ðn i a Þ and bulk oil ðn o a Þ and its distribution between these two domains at the threshold level of stability have been emphasized. The thermodynamics of transfer of 1-pentanol from the continuous oil phase to the interface have been evaluated. n i a ; n i a , standard Gibbs free energy ðDG 0 t Þ, standard enthalpy ðDH 0 t Þ, and standard entropy ðDG 0 t Þ of transfer process have been found to be dependent on the molar ratio of water to surfactant (x), type of nonionic surfactant and its content (X Brij-58 or Brij-78 ), oil and temperature. A correlation between ðDH 0 t Þ and ðDS 0 t Þ is examined at different experimental temperatures. Bulk surfactant composition dependent temperature insensitive microemulsions have been reported. Associated structural parameters, such as droplet dimensions and aggregation number of surfactant and cosurfactant at the droplet interface have been evaluated using a mathematical model after suitable modifications for mixed surfactant systems. In light of these parameters, the prospect of using these microemulsion systems for the synthesis of nanoparticles and the modulation of enzyme activity has been discussed. Correlations of the results in terms of the evaluated physicochemical parameters have been attempted.
Surfactants for microemulsions
Current Opinion in Colloid & Interface Science, 1997
Research effort in past years has focused on the •development of microemulsions with specific properties, namely, high solubilizing power and temperature insensitivity. Phase behavior studies have provided the foundations for this development. On the basis of mass balance analysis and the geometry of three-phase tie triangles, the composition of the surfactant films separating micro-water and oil domains in bicontinuous type microemulsions has been determined. This information allows a beller comparison of the solubilizing power .of surfactants. In addition, decisive progress has been made in the development of surfactant systems for the preparation of biocompatible microemulsions.
Journal of Pharmaceutical Sciences, 1998
The level of solubilization of the drug testosterone propionate into 2% w/w oil-in-water (o/w) microemulsions, stabilized by the nonionic surfactant polyoxyethylene 10-oleyl ether (Brij 96) and containing a range of oils, has been determined. Although testosterone propionate was readily soluble in the ethyl esters ethyl oleate, ethyl caprylate, and ethyl butyrate, and the triglycerides soybean oil, Miglyol 812, and tributryin, and the alkene 1-heptene, only microemulsions containing the ethyl esters and the triglyceride oils exhibited a significant increase in solubilization over the corresponding micellar solution (i.e., surfactant solution in the absence of oil). Furthermore, the increase in drug solubility observed in the microemulsion systems was not related to the solubility of the drug in the bulk oil. That is, while the smaller molecular volume oils, such as ethyl butyrate, exhibited a greater capacity for the drug, microemulsions containing these oils were only marginally better at solubilizing the drug than the corresponding micellar solution. In contrast, microemulsions containing the larger molecular volume oil, Miglyol 812, gave levels of drug solubilization almost three times those containing ethyl butyrate, yet the bulk capacity for drug in this oil was less than half that of ethyl butyrate. Light scattering and phase inversion temperature studies suggested that the structure of the microemulsion was sensitive to the oil being used, in that, at the low oil concentrations used in this study, the smaller molecular volume oils generally penetrated the interfacial surfactant monolayer in much the same way as a cosurfactant, causing an alteration, presumably a dilution, of the relatively concentrated polyoxyethylene region close to the hydrophobic core, thereby destroying one of the main loci of drug solubilization and counteracting any advantages encountered due to the high solubility of the drug in the bulk oil.
Analysis of polyethoxylated surfactants in microemulsion-oil–water systems
Analytica Chimica Acta, 2003
Oligomer distribution of polyethoxylated alcohol and polyethoxylated nonylphenol surfactants is studied by normal and reverse-phase high performance liquid chromatography (HPLC). A RP8 column is able to efficiently separate these surfactants according to their alkyl chain (lipophilic) group, while silica and amino columns separate them according to their polyether chain length (hydrophilic group). Polyethoxylated alcohol and polyethoxylated nonylphenol oligomers selectively partition between the microemulsion-oil-water phases of a Winsor III system. Partitioning of these oligomers was analyzed by HPLC with RI detection. The logarithm of the partition coefficient between the water and oil linearly increases with the number of ethylene oxide groups per molecule of oligomer. For a same ethoxylation degree, the partition coefficient of a polyethoxylated tridecanol is found to be higher than the one of the corresponding nonylphenol specie. On the other hand, a polyethoxylated nonylphenol exhibits a higher solubilization than the matching polyethoxylated alcohol.
Solubilisation of soybean oil in microemulsions using various surfactants
Food Hydrocolloids, 2006
Microemulsions are transparent, isotropic solutions of oil, water and surfactant (and possibly cosurfactant) which are thermodynamically stable, and have been much studied in terms of pharmaceutical and cosmetic applications. However, the application of microemulsions in foods has been limited both due to toxic or irritant nature of ionic surfactants and the difficulty of solubilising large triglycerides. Three surfactants, food-grade ethoxylated mono-and diglycerides (EMD) and phospholipids, and non-food-grade polyoxyethylene oleyl ether (POE) were examined for their ability to form microemulsions using soybean oil, and their areas of formation expressed on phase diagrams. Microemulsions prepared with EMD and phospholipids required the presence of a short-chain alcohol for formation. Both oil/water (o/w) and water/oil (w/o) microemulsions could be formed using EMD, and the microemulsion area of the phase diagram increased on addition of sucrose and increase in temperature. Depending on sucrose and ethanol concentrations, microemulsions formed with EMD were found to retain their integrity at temperatures below which they formed. Microemulsions could be formed using phospholipids, but only at high surfactant concentration and in the presence of a short-chain alcohol. O/w microemulsions containing 10% oil (w/w) were prepared with POE at surfactant concentrations of O20% (w/w). Dynamic light scattering of microemulsion samples diluted with water indicated particle radii of 6.5 nm. Freeze-fracture SEM showed the structures to be of a droplet type, however, this was more evident at higher surfactant/oil concentrations. The results indicated that it is possible to formulate microemulsions at low EMD and POE surfactant concentration. These microemulsions systems may potentially be used for encapsulation of oil-soluble bioactives, e.g. a-tocopherol, in food systems.
Model microemulsions containing vegetable oils part 1: Nonionic surfactant systems
Journal of the American Oil Chemists Society, 1989
aKarishamns AB, Division R&D, S-374 82 Karlshamn, Sweden and blnstitute for Surface Chemistry, S-114 86 Stockholm, Sweden Nonionic microemulsions containing triglycerides and fatty acid esters as lipophilic components have been studied. The phase inversion temperature (PIT) of the systems was determined by a conductometric method. Partial phase diagrams were constructed in the phase inversion temperature range. Water solubilization capacity of the nonionic surfactant systems studied was dependent on surfactant and oil types in analogy to ordinary hydrocarbon systems. The PIT:s increased with increased molecular weight for both esters and triglycerides.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000
Sub-zero temperature differential scanning calorimetry (SZT-DSC) has been applied to a model nonionic water-inoil 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.