Stig E. Friberg

Microemulsions — phase equilibria characterization, structures, applications and chemical reactions

Abstract The progress in understanding microemulsion structure on a molecular level as well as from extensive experimental studies of phase diagrams is reviewed. In this respect the studies involve both ionic and nonionic surfactants. Structures discussed involve the hard sphere model, the bicontinuous model, sponge phases and the flexible surface model. The progress in spectroscopic techniques (like NMR and TDS) together with scattering techniques, when applied to microemulsion systems, is also briefly discussed. Technical applications of microemulsions involve general applications as cleaning systems, fuels and in the field of crude oil exploitation. The last topic summarizes the use of the systems in EOR, acidizing and transport. The major emphasis of the review is in the utilization of microemulsions as systems in chemical reactions. These reactions involve preparation of inorganic particles, polymerization of organic monomers together with preparation of both organic and inorganic complexes and clusters. Enzyme catalyzed reactions involving the enzymes lipase, trypsin, α-chymotrypsin and alcohol dehydrogenase in different microemulsions are also summarized.

Solubilization of an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, in a surfactant-water system

Abstract The amphiphilic association structures were determined in the system; water, Laureth 4 (approximately C12(EO) 4), and the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate ([bmim[PF6]), using visual observation and small angle x-ray diffraction. The system showed a lamellar liquid crystal solubilizing the ionic liquid ([bmim[PF6]) to a maximum of 15%, an isotropic surfactant solution dissolving the ionic liquid to a maximum of 39%, an isotropic ionic liquid solution with less than 0.5% of water and surfactant and finally, an aqueous solution with only traces of surfactant and ionic liquid. The small angle x-ray diffraction results showed the ionic liquid to be solubilized into the lamellar liquid crystal without changing the dimensions of the amphiphile layer or the interlayer spacing dependence on the water content.

Phase changes during evaporation from a vegetable oil emulsion stabilized by a polyoxyethylene {20} sorbitanoleate, Tween® 80

The phase diagrams of the systems of water and polyoxyethylene {20} sorbitanoleate (Polysorbate-80) with soybean oil were determined and the phase changes during evaporation of water were followed microscopically. The phase changes observed during evaporation agreed with those predicted by the equilibrium phase diagram.

Equilibrium Topology and Partial Inversion of Janus Drops: A Numerical Analysis

The equilibrium topology of an aqueous Janus emulsion of two oils, O1 and O2, with water, W, [(O1+O2)/W], is numerically evaluated with the following realistic interfacial tensions (γ): γO2/W =5 mNu2009m(-1) , γO1/O2 =1 mNu2009m(-1) , and γO1/W varies within the range 4-5 mNu2009m(-1) , which is the limiting range for stable Janus drop topology. The relative significance of the two independently pivotal factors for the topology is evaluated, that is, the local equilibrium at the line of contact between the three liquids and the volume fraction of the two dispersed liquids within the drop. The results reveal a dominant effect of the local equilibrium on the fraction of the O2 drop surface that is covered by O1. In contrast, for a constant volume of O2, the impact of the interfacial tension balance on the limit of the coverage is modest for an infinite volume of O1. Interestingly, when the O1 volume exceeds this value, an emulsion inversion occurs, and the O1 portion of the (O1+O2)/W topology becomes a continuous phase, generating a (W+O2)/O1 Janus configuration.

Multivariate analysis of the size dependence of monodisperse silica particles prepared according to the sol-gel technique

Abstract The dependence of the size of the silica particles produced by a sol-gel process on constituent concentrations, reaction temperature and time was studied using reduced factorial design 2 6-2 . Much information is obtained with a few experiments. The data obtained are interpreted using multiple regression analysis. To account for the experimental results two models based on particle diameter and the other on total particle area are suggested. The full model with cross terms based on particle diameter explains 97.5% of the variation in particle size, while the model including the experimental variables explains only 18.4%. The full model based on total particle area explains 98.4% of the variance, while the model including only the main variables (tetraethyl orthosilicate and water concentration) explains 90%. The models are non-linear, suggesting that at least one of the variables is non-linear. The effects of changed levels of variables are explained on the basis of changed reaction rates.

The Coupling Action of a Hydrotrope and Structure Transition from Lamellar Liquid Crystal

Abstract The influence of SDS (a hydrotrope) on the region of stability of a microemulsion of water, sodium dodecyl sulfate (SDS), pentanol (C3OH) and p-xylene was determined. The addition of the hydrotrope united the O/W and W/O regions of the phase diagram enlarging the bicontinuous region by reducing the lamellar liquid crystal one. Hence, the phase behavior and the low angle x-ray measurements show that the stratum corneum coupling action of a hydrotrope is in

Selective emulsion inversion in an equilibrium Janus drop. 1. Unlimited space

The potential for a catastrophic inversion of one phase in a Janus emulsion drop was investigated by local equilibrium calculations of a single Janus drop of two mutually insoluble oils, O1 and O2, in an infinite aqueous continuous phase, (O1+O2)/W. The relative volume of the oil with less interfacial tension towards water, O2, was increased, while the radius of the O1 part of the drop was held constant at unity. The limiting fraction of O1 covered by O2 was calculated for infinite O2 volume for a selected interfacial tension combination. After the O2 volume reached infinity, the volume of the continuous aqueous phase was reduced to finite values, leading to a selective inversion of the emulsion from (O1+O2)/W to (W+O1)/O2. Thenceforward, further removal of the water led to an additional reduction of the size and radius of the water cap.

Vapour pressure of some fragrance ingredients in emulsion and microemulsion formulations

The vapour pressure of two fragrance raw materials, phenethyl alcohol and phenethyl acetate, in a microemulsion system is discussed against their participation in the different phases of the system. The results are used to evaluate the change of the fragrance vapour pressure during water evaporation from a typical emulsion system. Resume. Etude de la tension de vapeur de deux matieres premieres de parfum, le phenethylalcool et le phenethylacetate, dans un systeme de microemulsion, en rapport avec leur participation aux differentes phases du systeme. Les resultats sont utilises pour evaluer la modification de la tension de vapeur de parfum lors de levaporation deau dun systeme classique demulsion.

Topical Application of Retinyl Palmitate-Loaded Nanotechnology-Based Drug Delivery Systems for the Treatment of Skin Aging

The objective of this study was to perform a structural characterization and evaluate the in vitro safety profile and in vitro antioxidant activity of liquid crystalline systems (LCS) with and without retinyl palmitate (RP). LCS containing polyether functional siloxane (PFS) as a surfactant, silicon glycol copolymer (SGC) as oil phase, and water in the ratios 30u2009:u200925u2009:u200945 and 40u2009:u200950u2009:u200910 with (OLSv = RP-loaded opaque liquid system and TLSv = RP-loaded transparent liquid system, respectively) and without (OLS and TLS, respectively) RP were studied. Samples were characterized using polarized light microscopy (PLM) and rheology analysis. In vitro safety profile was evaluated using red cell hemolysis and in vitro cytotoxicity assays. In vitro antioxidant activity was performed by the DPPH method. PLM analysis showed the presence of lamellar LCS just to TLS. Regardless of the presence of RP, the rheological studies showed the pseudoplastic behavior of the formulations. The results showed that the incorporation of RP in LCS improved the safety profile of the drug. In vitro antioxidant activity suggests that LCS presented a higher capacity to maintain the antioxidant activity of RP. PFS-based systems may be a promising platform for RP topical application for the treatment of skin aging.

Vapour pressure of a fragrance ingredient during evaporation in a simple emulsion

The phase diagram water, phenethyl alcohol and laureth 4 was determined and the variation of the vapour pressure of the alcohol was determined during evaporation using gas chromatographic head‐space analysis. The phase changes during evaporation were estimated from the phase diagram and compared to the appearance of the emulsion using optical microscopy. The transfer of the fragrance ingredient between different phases during the process was estimated and its measured vapour pressures compared to those calculated from values of earlier determination in different phases in the system. The agreement was good. On a elabore le diagramme de phase eau, alcool phenethylique et laureth 4 et on a determine la variation de la tension de vapeur de lalcool durant levaporation en utilisant lanalyse par chromatographie gazeuse a injection directe en tete de colonne. Les changements de phase durant levaporation sont estimes a partir du diagramme de phase et compares a laspect de lemulsion par microscopie optique. On a estime le transfert de lingredient parfume entre les differentes phases durant le processus et ses tensions de vapeur mesurees ont ete comparees a celles calculees a partir de valeurs determinees anterieurement dans differentes phases du systeme. La concordance est satisfaisante.