M.C. Alfaro

Adsorption at the biocompatible α-pinene–water interface and emulsifying properties of two eco-friendly surfactants

In this contribution, we provide an accurate characterization at the α-pinene/water interface of two commercial polyoxytheylene glycerol ester surfactants which differ in the number of ethylene oxide (EO) groups, comprising a systematic analysis of interfacial pressure isotherms, dynamic curves, interfacial rheology and emulsifying properties. Polyoxyethylene glycerol esters derived from cocoa oil are non-ionic surfactants obtained from a renewable source which fulfill the environmental and toxicological requirements to be used as eco-friendly emulsifying agents. α-Pinene is a renewable biosolvent completely insoluble in water, which could find numerous applications. Interfacial rheology and equilibrium interfacial pressure data fitted a rigorous reorientation model that assumes that the surfactant molecules, when adsorbed at the interface, can acquire two orientations. The surfactant with the highest number of EO groups (Levenol C201) turned out to be more surface active at the α-pinene/water interface. In addition, the surfactant with the lowest number of EO groups (Levenol H&B) is solubilized into the adjacent oil phase. Slightly concentrated α-pinene emulsions were obtained using both surfactants. Nevertheless, more stable α-pinene emulsions with smaller droplet sizes and lower polidispersity were obtained when Levenol C201 was used as emulsifier instead of Levenol H&B. The systematic characterization presented in this work provides important new findings on the interfacial and emulsifying properties of polyoxytheylene glycerol ester surfactants, which can be applied in the rational development of new biocompatible products.

Development and rheological properties of ecological emulsions formulated with a biosolvent and two microbial polysaccharides

The influence of gum concentration and rhamsan/welan gum ratio on rheological properties, droplet size distribution and physical stability of eco-friendly O/W emulsions stabilized by an ecological surfactant were studied in the present work. The emulsions were prepared with 30wt% α-pinene, a terpenic solvent and an ecological alternative for current volatile organic compounds. Rheological properties of emulsions showed an important dependence on the two studied variables. Flow curves were fitted to the Cross model and no synergistic effect between rhamsan and welan gums was demonstrated. Emulsions with submicron mean diameters were obtained regardless of the gum concentration or the rhamsan/welan ratio used. Multiple light scattering illustrated that creaming was practically eliminated by the incorporation of polysaccharides. The use of rhamsan and welan gums as stabilizers lead to apparent enhancements in emulsion rheology and physical stability.

Rheological behavior of aqueous dispersions containing blends of rhamsan and welan polysaccharides with an eco-friendly surfactant.

Small amplitude oscillatory shear and steady shear flow properties of rhamsan gum and welan gum dispersions containing an eco-friendly surfactant (a polyoxyethylene glycerol ester) formulated to mimic the continuous phase of O/W emulsions were studied using the surface response methodology. A second order polynomial equation fitted the influence of surfactant concentration, rhamsan/welan mass ratio and total concentration of polysaccharides. Systems containing blends of rhamsan and welan did not show synergism but thermodynamic incompatibility and made it possible to adjust the linear viscoelastic and low shear rate flow properties to achieve values in between those of systems containing either rhamsan or welan as the only polysaccharide. All the systems studied exhibited weak gel rheological properties as the mechanical spectra displayed the plateau or rubber-like relaxation zone, the linear viscoelastic range was rather narrow and flow curves presented shear thinning behavior, which fitted the power-law equation. While mechanical spectra of the systems studied demonstrated that they did not control the linear viscoelastic properties of the corresponding emulsions, the blend of rhamsan and welan gums was able to control the steady shear flow properties.

Caracterización reológica de una suspoemulsión comercial para uso agroquímico

Se estudian las propiedades reologicas de una suspoemulsion comercial para uso agroquimico. Se comparan los resultados obtenidos mediante curvas de flujo y ensayos en cizalla oscilatoria de baja amplitud para cinco temperaturas distintas en el intervalo de 5 a 25oC. Las curvas de flujo, ponen de manifiesto que la suspoemulsion se caracteriza por presentar un comportamiento pseudoplastico, menos acusado a medida que aumenta la temperatura, que se ajusta al modelo de Sisko. Barridos de esfuerzo realizados a 0,1Hz permiten determinar el reducido rango viscoelastico lineal de la suspoemulsion, que depende de la temperatura. Los espectros mecanicos, entre 3Hzy 0,01 Hz, revelan que el sistema manifiesta propiedades viscoelasticas con un comportamiento tipico de gel debil. La aparicion de un minimo en el valor de G” respecto a la frecuencia ha permitido estimar el modulo plateau, el cual desciende con el aumento de temperatura segun una ecuacion tipo Arrhenius. Aun asi, la suspoemulsion presenta un caracter elastico que favorece su estabilidad fisica con el tiempo de almacenamiento. Se ha demostrado ademas que el sistema no sigue la regla de Cox-Merz.

Physical stability of N,N-dimethyldecanamide/α-pinene-in-water emulsions as influenced by surfactant concentration

In recent years, interest in submicron emulsions has increased due to their high stability and potential applications in the encapsulation and release of active ingredients in many industrial fields, such as the food industry, pharmaceuticals or agrochemicals. Furthermore, the social demand for eco-friendly solutions to replace hazardous solvents in many dispersion formulations has steadily risen. In this study, the influence of surfactant concentration on the formation and physical stability of submicron oil-in-water emulsions using a high-pressure dual-channel homogenizer (microfluidizer) has been investigated. The formulation involved the use of a blend of two green solvents (N,N-dimethyldecanamide and α-pinene) as dispersed phase and a nonionic polyoxyethylene glycerol ester derived from coconut oil as emulsifier (Levenol® C-201), which enjoys a European eco-label. Therefore, these emulsions may find applications as matrices for agrochemicals. Physical stability and rheological properties of the emulsions studied showed an important dependence on the eco-friendly surfactant concentration. The lowest surfactant concentration (1wt%) yielded the onset of a creaming process after a short aging time and was not enough to avoid recoalescence during emulsification. On the other hand, the higher surfactant concentrations (4-5wt%) resulted in depletion flocculation, which in turn triggered emulsion destabilization by coalescence. The optimum physical stability was exhibited by emulsions containing intermediate surfactant concentrations (2-3wt%) since coalescence was hardly significant and the onset of a weak creaming destabilization process was substantially delayed.

Rheology of Spray-Dried Egg Yolk-Xanthan Gum Aqueous Dispersions

Protein-polysaccharide systems have not only scientific interest in the effort to understand the behaviour of complex multicomponents systems, but they also have many technological implications, above all in the development of new food products. They are particularly useful for the formulation of low-fat stuffs and for the enhancement of the funcionality of “natural” food ingredients. In fact, they are the most important structure forming macromolecular ingredients in foods.

Relaxation and Retardation Spectra of Lamellar Liquid Crystals in a Toluene/Nonionic Surfactant/Water System

Hydrophilic and lipophilic chemicals may be solubilized into either micelles or lyotropic liquid crystals (LC) forming monophasic ternary or more complex systems, which have interesting practical applications in detergency, emulsion technology, cosmetics, biology, monodispersed fine particles, as media for chemical reactions, etc. Lamellar liquid crystals (Lα), consist of surfactant bilayers, which may solubilize apolar chemicals among the hydrocarbon chains, separated by an aqueous medium that can incorporate hydrophilic substances. The whole microstructure is formed by the combination of clusters of flexible bilayers, each of them characterized by a director which defines the main orientation of the so-called monodomain. In other words, the Lα micro structure is formed by connected monodomains with random orientation so that from a macroscopic point of view the polidomain texture looks disoriented and with structural defects. Additionally, some vesicles may also be present.