Alicia Maestro

Nano-emulsions prepared by the phase inversion composition method: Preparation variables and scale up

The aim of this work is to study, through experimental design, the effect of vessel geometry and scale-up in the properties of nano-emulsions prepared through the phase inversion composition method (PIC). Results show that a proper mixing is crucial for small droplet-sized nano-emulsions, especially when remaining free oil is found together with the key liquid crystal phase formed during the emulsification process. In these cases, mixing must be near the perfect mixed model. Proper geometries must be selected to promote a good mixture. Small addition rates V(ad) and high mixing rates omega promote the necessary mixing level. However, results indicate that, if free oil remains together with liquid crystal formed during emulsification, a too high omega could promote coalescence of oil droplets. When a cubic liquid crystal phase Pm3n is formed instead during emulsification, without free oil, coalescence is not promoted, probably due to the extremely high viscosity. For the system where Pm3n is formed during emulsification, scale-up cannot be done, as it would be expected, maintaining adimensional variables--Reynolds, Re, and adimensional time. A perfect correspondence between scales is observed when the total addition time and the lineal mixing rate are maintained between scales instead. Re, i.e. the ratio between inertial and viscous forces, does not seem adequate to describe the system, as inertial forces are worthless due to the extremely high viscosity.

Study of nano-emulsion formation by dilution of microemulsions

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.

Preparation of Span 80/oil/water highly concentrated emulsions: Influence of composition and formation variables and scale-up

The influence of composition and preparation variables on the properties of W/O highly concentrated emulsions obtained in the system Span 80/oil/water was studied. Emulsions prepared with decane, dodecane and hexadecane were analysed. Stability of emulsions was found to depend on the oil as follows: stability of hexadecane emulsions > dodecane > decane. It was attributed to the lower solubility of water in the oil with longer chain. Experimental design tools were used to study the influence of composition and preparation variables and scale-up on the droplet size and polydispersity of emulsions formed. The most important factor was found to be the surfactant-oil ratio, SO, as more surfactant could stabilize more interface, but other preparation variables, like mixing rate, omega, were also found to influence the droplet size and polydispersity. The proper scale-up variables were found not to correspond to the dimensionless variables commonly used in scale-up studies, but total addition time, t(t), and angular mixing velocity, omega, seemed to be the proper ones.

Thickening mechanism of associative polymers

Steady state viscosity and viscoelasticity of HMHEC solutions were studied. Viscosity increases with concentration due to a reinforcement of the micellar network. High shear rate viscosities are independent of temperature. Two relaxation processes were observed, the long one related to the lifetime of the hydrophobic junction and the short related to rapid Rouse-like relaxations of the free chains. When SDS is added, mixed micelles form that reinforce the network up to an optimum [SDS]/[HMHEC] ratio. Above this ratio, the micelles in excess isolate the polymer chains, the long relaxation process disappears and Rouse-like relaxations occur, corresponding to rapid movements of free chains.

Ion exchange columns for the synthesis of ordered mesoporous materials

Structured mesoporous materials were successfully synthetized using an ion exchange column as protons source. Operating conditions were set in order to obtain mesostructured materials using short operation times. This method opens the door to the industrial synthesis of this kind of materials. The ordered mesoporous materials were obtained using sodium silicate solution as a precursor and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO19PO39EO19 denoted as P84) was used as structure-directing agent. The influence of the composition variables (surfactant and precursor concentrations) was studied. The materials were characterized by TEM, SAXS and nitrogen adsorption–desorption isotherms to determine their specific surface area. A response surface was obtained, showing that in the studied range the ratio sodium silicate:water was the most significant parameter in order to obtain the materials with a well-structured pore arrangement. The use of sodium silicate solution as silica source instead of TEOS or TMOS, and the possibility of obtaining a material through an ion exchange column are important from the application point of view because of the relatively cheap raw materials and equipments. Presented results indicate that for every precursor:water:surfactant system an optimum experimental operating conditions must be selected once the reactants flow rate has been set.