Jaime Ruiz-Garcia

Foam and cluster structure formation by latex particles at the air/water interface

We report the formation of two-dimensional foam and cluster structures by spherical polystyrene particles trapped at the air/water interface. The colloidal foam is a transient structure that evolves to the formation of clusters, but clusters can also be formed after deposition of the sample. We also observed the formation of small aggregates, whose formation along with the cluster stabilization can be explained in terms of a balance between electrostatic repulsive and van der Waals attractive interactions.

Chemotherapy pro-drug activation by biocatalytic virus-like nanoparticles containing cytochrome P450.

This work shows, for the first time, the encapsulation of a highly relevant protein in the biomedical field into virus-like particles (VLPs). A bacterial CYP variant was effectively encapsulated in VLPs constituted of coat protein from cowpea chlorotic mottle virus (CCMV). The catalytic VLPs are able to transform the chemotherapeutic pro-drug, tamoxifen, and the emerging pro-drug resveratrol. The chemical nature of the products was identified, confirming similar active products than those obtained with human CYP. The enzymatic VLPs remain stable after the catalytic reaction. The potential use of these biocatalytic nanoparticles as targeted CYP carriers for the activation of chemotherapy drugs is discussed.

Computer simulations of confined colloidal systems at the air/water interface

We present Monte Carlo simulations in the NV T ensemble for spherical particles of diameter σ interacting via a hard-core potential with a squareshoulder (SS) repulsive barrier, a square-well (SW) attraction, and a second SS repulsion. This discrete potential is used to mimic the pair interaction in confined colloidal systems at the air/water interface. The SW attraction represents a secondary minimum for large interparticle distances, and the SS repulsion is a shallow secondary maximum after the secondary minimum. The effect of the SS range λr σ is studied for the cases λr = 0, 6, and 7. The simulation results for the last two cases indicate the important role of the presence of the secondary maximum in the interaction potential, since they are able to reproduce the main features observed in colloidal particles trapped at the air/water interface, such as clustering, chain formation, foams, and the presence of voids.

Living poly‐α‐methylstyrene near the polymerization line. II. Phase diagram in methylcyclohexane

We present the experimental determination of the liquid–liquid coexistence curve of living poly‐α‐methylstyrene (initiated by n‐butyllithium) in methylcyclohexane. We measured the coexistence curve by measuring the phase separation temperatures of a set of samples of different mole fractions of the initial monomer, x*m. All the samples had the same ratio, r(=0.008), of the mole fraction of the initiator to the mole fraction of the monomer. We also measured the polymerization line by measuring the temperatures at which increases in viscosity signaled the onset of polymerization. The measured upper critical solution point for this system is at a temperature of 274±1 K and at x*m = 0.18 ± 0.02. At this x*m, the polymerization temperature Tp is 285 K, well above the critical temperature. Tp decreases as x*m decreases, so that the polymerization line meets the coexistence curve at about x*m = 0.12. We compare the predictions of a lattice model which is equivalent to the mean field limit of the dilute n→0 magne...

Localized oscillations and Fraunhofer diffraction in crystalline phases of a monolayer

Localized oscillations present in the crystalline phases of the heneicosanoic acid Langmuir monolayer were studied in detail. They appear like blinking interference rings, when observed with Brewster angle microscopy. Monolayers with localized oscillations were transferred on mica to be characterized by atomic force microscopy. We found granules produced by the expulsion of matter from the monolayer. However, these granules are too short to produce Newton’s rings; the common belief of the origin of the interference rings in the field of Langmuir monolayers. The analysis of the light intensity distribution and the sizes of the rings are consistent with Airy patterns produced by Fraunhofer diffraction due to the reflected light from the multilayer granules. The origin of the blinking of these patterns is still unclear.

Crystallite structure formation at the collapse pressure of fatty acid Langmuir films

We report isotherm and atomic force microscopy studies of collapsed Langmuir monolayers of fatty acids. The Langmuir monolayers were overcompressed in the range 7–40 °C and transferred onto mica after the sharp pressure drop when the collapse pressure was reached. Collapsed material was observed by AFM, which revealed that the multilayers are indeed three-dimensional crystallites. We found that the shape of the crystallites depends on the collapse temperature, the phase from which the collapse occurs and/or the chain length. However, at higher temperatures the collapsed films no longer show a well defined crystallite formation, but rather a more heterogeneous melt-like pattern. We associated the crystallite formation with known bulk crystal phases of the fatty acids.

Brewster angle microscopy of fullerene monolayers

The aim of this paper is to present a direct observation by means of Brewster angle microscopy of Langmuir films made of C60 along the process of their compression. We found coexistence of a gas and a condensed phase at low area densities. Our results agree with the formation of multilayers even at low area densities. We made compressions of the films at several speeds, with rapid compressions we found that the condensed phase formed foam-like structures and circular domains of different sizes at very small area densities.

Soft purification of N-doped and undoped multi-wall carbon nanotubes

A soft method for purifying multi-wall carbon nanotubes (N-doped and undoped) is presented. The technique includes a hydrothermal/ultrasonic treatment of the material in conjunction with other subsequent treatments, including the extraction of polyaromatic compounds, dissolution of metal particles, bundle exfoliation, and uniform dispersion. This method avoids harsh oxidation protocols that burn (via thermal treatments) or functionalize (by introducing chemical groups) the nanotubes. We show a careful analysis of each purification step and demonstrate that the technique is extremely efficient when characterizing the materials using scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), scanning tuneling electron microscopy (STEM), x-ray powder diffraction (XRD), diffuse reflectance Fourier transform infrared (DRFTIR) spectroscopy and thermogravimetric analysis (TGA).

Plant-based porcine reproductive and respiratory syndrome virus VLPs induce an immune response in mice.

Porcine reproductive and respiratory syndrome virus (PRRSV) significantly affects the swine industry worldwide. An efficient, protective vaccine is still lacking. Here, we report for the first time the generation and purification of PRRSV virus like particles (VLPs) by expressing GP5, M and N genes in Nicotiana silvestris plants. The particles were clearly visible by transmission electron microscopy (TEM) with a size of 60-70 nm. Hydrodynamic diameter of the particles was obtained and it was confirmed that the VLPs had the appropriate size for PRRS virions and that the VLPs were highly pure. By measuring the Z potential we described the electrophoretic mobility behavior of VLPs and the best conditions for stability of the VLPs were determined. The particles were immunogenic in mice. A western blot of purified particles allowed detection of three coexpressed genes. These VLPs may serve as a platform to develop efficient PRRSV vaccines.

Evolution of a colloidal soap-froth structure

We report the evolution of a quasi-two-dimensional cellular structure. This soap-froth-like structure is formed by 2.24μm colloidal particles trapped at the air/water interface. The froth evolves mainly through one of the modes of the T2 mechanism, the inverse mitosis process, and in minor proportion through the T1 or side switching mechanism. In addition, particle rearrangements can also be observed during the evolution. Eventually, the colloidal soap-froth evolves towards the formation of colloidal clusters, which detach from the edges of the colloidal froth. The cell side distribution is similar to distributions from other froth-forming systems and follows the Aboav–Weaire law. Other statistical comparisons are also made with other froth-forming systems and, in general, we found similar behaviour.