Jordi Esquena

A Liquid‐Crystalline Single‐Molecule Magnet with Variable Magnetic Properties

This work was supported by the Marie Curie EST FuMaSSEC, EU NoE MAGMANet (515767-2), EMOCIONA (CTQ2006-06333/BQU), Grup de Recerca de Catalunya (2009 SGR-516) and Molecular Nanoscience (CSD2007-00010) and Molchip (MAT2009-13977-C03) projects.

Shaping Supramolecular Nanofibers with Nanoparticles Forming Complementary Hydrogen Bonds

Functionalized gold nanoparticles with complementary H-bonding groups can control the secondary structure of xerogel fibers formed by a molecular conductor thanks to their incorporation into the nanowires, which show metal-like conductivity once doped without the need for annealing. The picture shows a photograph of the xerogel, TEM images of Au particles in the gel and a single fiber, and an AFM image revealing the texture of the gel.

Studies of the relation between phase behavior and emulsification methods with nanoemulsion formation

The main aim of this work was to study the relationship between the type of phases present during the emulsification process, the order of addition of components and the droplet size of the resulting emulsions. In this study, a pseudoternary water/poly(oxyethylene) nonionic surfactant/decane system was chosen as a model system to form oil-in-water emulsions at 25 °C. The phase behavior of the model system was determined at constant temperature in order to know the equilibrium phases and also those involved in the emulsification process. The low-energy emulsification methods studied were A. Addition of oil to an aqueous surfactant dispersion. B. Addition of water to a surfactant solution in oil. C. Mixing preequilibrated samples of the components.

Highly concentrated (gel) emulsions, versatile reaction media

Abstract Highly concentrated (gel) emulsions are characterised by dispersed phase volume fractions exceeding 0.74, the critical value for the most compact packing of monodispersed undistorted spheres. Their structure consists of polyhedral droplets separated by thin films of continuous phase, a structure resembling gas–liquid foams. Their rheological properties vary from elastic to viscoelastic having a gel appearance. One of the most promising applications is their use as reaction media. The recent advances in the preparation of low-density polymeric materials (solid foams, aerogels) are reviewed and new applications are described. These include the preparation of dual meso/macroporous inorganic oxide materials and the use of gel emulsions as alternative to conventional solvent media in chemical and enzyme-catalysed reactions.

Formation and stability of nano-emulsions in mixed nonionic surfactant systems

The formation of nano-emulsions has been studied in water/ mixed nonionic surfactant/oil systems using two emulsification methods. In one method, the composition was kept constant and the temperature was changed (phase-inversion temperature, PIT, method), while in the other method, water was added dropwise to a solution of the mixed surfactants in oil at constant temperature (method B). The droplet size and stability were determined as a function of surfactant mixing ratio, W1, at 25 °C. The droplet size of nano-emulsions obtained by the PIT method is practically independent of W1 and falls in the range 60-80 nm. In contrast, the droplet size of nano-emulsions prepared by method B, is highly dependent on W1 and varies between 60 and 300 nm. At W1 values where the PIT or the hydrophile—lipophile balance temperature (Thlb) of the system is close to 25 °C, the droplet sizes of the nano-emulsions are similar for both emulsification methods. There are three equilibrium phases of the latter compositions: an aqueous micellar solution or oil-in-water microemulsion (W m), a lamellar liquid-crystalline phase and an oil phase (O) in addition, these nano-emulsions showed higher kinetic stability than those with lower W 1 values (higher T hlb) and consisting of two liquid phases (W m + O).

Macroporous polymers obtained in highly concentrated emulsions stabilized solely with magnetic nanoparticles.

Magnetic macroporous polymers have been successfully prepared using Pickering high internal phase ratio emulsions (HIPEs) as templates. To stabilize the HIPEs, two types of oleic acid-modified iron oxide nanoparticles (NPs) were used as emulsifiers. The results revealed that partially hydrophobic NPs could stabilize W/O HIPEs with an internal phase above 90%. Depending upon the oleic acid content, the nanoparticles showed either an arrangement at the oil-water interface or a partial dispersion into the oil phase. Such different abilities to migrate to the interface had significant effects on the maximum internal phase fraction achievable and the droplet size distribution of the emulsions. Highly macroporous composite polymers were obtained by polymerization in the external phase of these emulsions. The density, porosity, pore morphology and magnetic properties were characterized as a function of the oleic acid content, concentration of NPs, and internal phase volume of the initial HIPEs. SEM imaging indicated that a close-cell structure was obtained. Furthermore, the composite materials showed superparamagnetic behavior and a relatively high magnetic moment.

A study on the influence of emulsion droplet size on the skin penetration of tetracaine

Objectives/Aims: The influence of emulsion droplet size on the skin penetration of a model drug, tetracaine, was studied. For this purpose, in vitro dermal and transdermal delivery of tetracaine from 6 emulsions (3 macro-emulsions with droplet sizes >1 µm and 3 nano-emulsions with droplet sizes <100 nm) were tested. Methods: Two approaches were used: in the first one, the composition of the emulsions was kept constant, while in the second one, the surfactant concentration in the aqueous phase was kept constant by varying the overall surfactant concentration. Results: The results from emulsions differing only in droplet size did not provide statistically significant evidence for the anticipated increase in transdermal or dermal delivery (after 24 h) when reducing emulsion droplet size. The same results were obtained when the surfactant concentration in the aqueous phase was kept constant, indicating that there is no influence of emulsion droplet size on the skin penetration of tetracaine within the droplet size range studied. Conclusion: This is in contrast to what has been reported in various publications that claim penetration to increase with reducing droplet size. It should be noted that the results reported so far are based on emulsions that apart from droplet size also differed in composition and/or system components.

Water-in-water (W/W) emulsions

The author greatly acknowledges the financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2014-52687-C3-1-P project) and Marie Sklodowska Curie Initial Training Networks (FP7-PEOPLE-2013-ITN, BIBAFOODS project). The author also acknowledges support from Generalitat de Catalunya (2014SGR1655 and TECCIT15-1-0009) and Centro de Investigacion Biomedica en Red de Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN).

Preparation of monodisperse silica particles in emulsion media

Abstract The main aim of this work was to prepare monodisperse silica particles with specific properties suitable for chromatographic adsorbents. Silica particles were obtained in W/O emulsions by reaction of tetraethyl orthosilicate, using either NH 3 or HCl as catalysts. Emulsions were prepared by physicochemical, low energy emulsification methods. Monodisperse particles were obtained by using an appropriate emulsification method and by controlling emulsion stability during reaction. Silica particles, with mean sizes from 2 μm to 1000 μm, were prepared using HCl as a catalyst while NH 3 produced particles with mean sizes from 0.5 μm to 10 μm. The size was controlled by the mixing ratio between two different type of surfactants. Silica particles were characterised by optical and electron microscopy, nitrogen sorption, FTIR, small angle X-ray scattering and thin layer chromatography. The results showed that monodisperse spherical particles with a high specific surface, appropriate for chromatographic purposes, can be prepared in emulsion media using HCl as a catalyst.

Preparation of mesoporous/macroporous materials in highly concentrated emulsions based on cubic phases by a single-step method

A novel and simple single-step method for the preparation of meso/macroporous silica materials is described, which consists in templating in highly concentrated emulsions with a cubic liquid crystal in the continuous phase. Tetraethyl orthosilicate (TEOS) was solubilized in the aqueous continuous phase of highly concentrated emulsions stabilized by C(12)(EO)(8) and a PEO-PPO-PEO block copolymer nonionic surfactant, with a cubic liquid crystalline phase of the Fd3m type. The resulting silica materials were characterized by small-angle X-ray scattering, nitrogen sorption and transmission electron microscopy. The results showed that a dual pore size distribution was obtained, consisting of mesopores in the nanometer range and macropores between 1 and 5 μm. These dual meso/macroporous silicas with bimodal pore size distribution can possess specific surface areas higher than 400 m(2)/g.