Jaime Martín

Tailored polymer-based nanofibers and nanotubes by means of different infiltration methods into alumina nanopores.

Template synthesis is one of the most effective methods for the preparation of one-dimensional polymer-based nanostructures (1DPNs). Both hollow nanotubes and solid nanorods or nanofibers with tailored dimensions can be obtained by simply templating a porous material with suitable pore size. The mechanism of polymer infiltration into the pores is also very important in order to obtain the desired one-dimensional nanostructures and to control their final morphology. In this study, several infiltration methods were explored with the aim to obtain different 1DPNs. It was shown that, with these infiltration methods, it is possible to obtain nanofibers and nanotubes of any diameter and length composed of polymers with a wide chemical nature (poly(methyl methacrylate), poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidene fluoride), etc.), or even composed of nanoparticulate composites. Finally, the selection of infiltration method for desired nanostructure is discussed.

Raman intensities of ethane and deuterated derivatives

Experimental gas phase Raman scattering differential cross sections and depolarization ratios of ethane and its deuterated derivatives are reported. A consistent interpretation of these data is accomplished in the frame of the bond polarizability model. The bond polarizability derivatives ∂αCH/∂rCH here obtained are, within the estimated uncertainties, the same as for other hydrocarbon molecules not only for the mean polarizability but for the anisotropy as well. On the other hand, the C–C bond properties are proved to be essentially the same in ethane and in diamond. In ethane isotopic species with synclinal and antiperiplanar conformers the experimental intensities are not always in the ratio 2:1. A satisfactory explanation of this apparent anomaly is achieved on the basis of the calculated Raman tensors of homologous normal modes which are quite different in some cases.

Confinement effects on the crystallization of poly(ethylene oxide) nanotubes.

In this work, we show the effects of nanoconfinement on the crystallization of poly(ethylene oxide) (PEO) nanotubes embedded in anodized aluminum oxide (AAO) templates. The morphological characteristics of the hollow 1D PEO nanostructures were evaluated by scanning electron microscopy (SEM). The crystallization of the PEO nanostructures and bulk was studied with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The crystallization of PEO nanotubes studied by DSC is strongly influenced by the confinement showing a strong reduction in the crystallization temperature of the polymer. X-ray diffraction (XRD) experiments confirmed the isothermal crystallization results obtained by DSC, and studies carried out at low temperatures showed the absence of crystallites oriented with the extended chains perpendicular to the pore wall within the PEO nanotubes, which has been shown to be the typical crystal orientation for one-dimensional polymer nanostructures. In contrast, only planes oriented 33, 45, and 90° with respect to the plane (120) are arranged parallel to the pores main axis, indicating preferential crystal growth in the direction of the radial component. Calculations based on classical nucleation theory suggest that heterogeneous nucleation prevails in the bulk PEO whereas for the PEO nanotubes a surface nucleation mechanism is more consistent with the obtained results.

Study of the curing process of a vinyl ester resin by means of TSR and DMTA

Abstract The curing reaction of a vinyl ester resin (VER), using methyl ethyl ketone peroxide (MEKP) as initiator and cobalt hexanoate (HxCo) as promoter has been studied by thermal scanning rheometry (TSR) and dynamic-mechanical thermal analysis (DMTA) under isothermal conditions. The gel time, which is defined by several criteria, has been utilized to determine the apparent activation energy (Ea) of the process. Furthermore, an empirical model has been used to predict the change of complex viscosity (η∗) with time, and assuming a first order kinetics, a new value for Ea is obtained independent of HxCo concentration. Finally, the vitrification time has been obtained from DMTA experiments.

High-aspect-ratio and highly ordered 15-nm porous alumina templates

Ordered anodic aluminum oxide (AAO) templates with pores <15 nm in diameter and an aspect ratio (length-to-diameter ratio) above 3 × 10(3) have been fabricated using a nonlithographic approach; specifically, by anodizing aluminum in an ethylene-glycol-containing sulfuric acid electrolyte. The pores are the smallest in diameter reported for a self-ordered AAO without pore aspect-ratio limitations and good ordering, which opens up the possibility of obtaining nanowire arrays in the quantum confinement regime that is of interest for efficient thermoelectric generators. The effect of the ethylene glycol addition on both the pore diameter and the ordering is evaluated and discussed. Moreover, 15-nm-diameter Bi(2)Te(3) and poly(3-hexyl thiophene) (P3HT) nanowires have been prepared using these AAO templates. As known, Bi(2)Te(3) is currently the most efficient thermoelectric bulk material for room-temperature operations and, according with theory, its Seebeck coefficient should be increased when it is confined to nanowires with diameters close to 10 nm. On the other hand, P3HT is one of the main candidates for integrating organic photovoltaic and thermoelectric devices, and its properties are also proposed to increase when it is confined to nanoscale structures, mainly due to molecular orientation effects.

Ordered three-dimensional interconnected nanoarchitectures in anodic porous alumina

Three-dimensional nanostructures combine properties of nanoscale materials with the advantages of being macro-sized pieces when the time comes to manipulate, measure their properties, or make a device. However, the amount of compounds with the ability to self-organize in ordered three-dimensional nanostructures is limited. Therefore, template-based fabrication strategies become the key approach towards three-dimensional nanostructures. Here we report the simple fabrication of a template based on anodic aluminum oxide, having a well-defined, ordered, tunable, homogeneous 3D nanotubular network in the sub 100 nm range. The three-dimensional templates are then employed to achieve three-dimensional, ordered nanowire-networks in Bi2Te3 and polystyrene. Lastly, we demonstrate the photonic crystal behavior of both the template and the polystyrene three-dimensional nanostructure. Our approach may establish the foundations for future high-throughput, cheap, photonic materials and devices made of simple commodity plastics, metals, and semiconductors.

Neutron scattering study of the dynamics of a polymer melt under nanoscopic confinement

Poly(ethylene oxide) confined in an anodic aluminum oxide solid matrix has been studied by different neutron scattering techniques in the momentum transfer (Q) range 0.2<or=Q=/Q/<or=1.9 A(-1). The cylindrical pores of the matrix present a diameter (40 nm) much smaller than their length (150 microm) and are parallel and hexagonally ordered. In particular, we investigated the neutron intensity scattered for two orientations of the sample with respect to the incident beam, for which the Q direction was either parallel or perpendicular to the pores for a scattering angle of 90 degrees . Diffuse neutron scattering at room temperature has shown that the aluminum oxide has amorphous structure and the polymer in the nanoporous matrix is partially crystallized. Concerning the dynamical behavior, for Q<1 A(-1), the spectra show Rouse-like motions indistinguishable from those in the bulk within the uncertainties. In the high-Q limit we observe a slowing down of the dynamics with respect to the bulk behavior that evidences an effect of confinement. This effect is more pronounced for molecular displacements perpendicular to the pore axis than for parallel displacements. Our results clearly rule out the strong corset effect proposed for this polymer from nuclear magnetic resonance (NMR) studies and can be rationalized by assuming that the interactions with the pore walls affect one to two adjacent monomer monolayers.

Cellular interactions of biodegradable nanorod arrays prepared by nondestructive extraction from nanoporous alumina

Biodegradable extracellular matrices (ECMs) consisting of mechanically stable arrays of aligned poly(lactide) nanorods (nanorod diameter ≈ 200 nm; lattice constant ≈ 500 nm) with areas up to 9 cm2 were prepared by nondestructive extraction from recyclable self-ordered nanoporous alumina hard templates. Fibroblasts formed dense tissue layers on the heparin/gelatin activated nanorod arrays, showed excellent adhesion and exhibited a highly elongated morphology such as in natural tissue. The synthetic approach reported here combining advantages of top-down lithography (well-defined topography) and self-assembly (low costs, high throughput, feature size in the 100 nm range) may yield ECMs for biomedical applications. Remarkably, on microrod arrays with four times larger feature sizes the fibroblasts were significantly less elongated and their proliferation was strongly reduced.

Patterns of constitutive and IFN-γ inducible expression of HLA class II molecules in human melanoma cell lines

Major histocompatibility complex (MHC) class II proteins (HLA-DR, HLA-DP and HLA-DQ) play a fundamental role in the regulation of the immune response. The level of expression of human leukocyte antigen (HLA) class II antigens is regulated by interferon-γ (IFN-γ) and depends on the status of class II trans-activator protein (CIITA), a co-activator of the MHC class II gene promoter. In this study, we measured levels of constitutive and IFN-γ-induced expression of MHC class II molecules, analysed the expression of CIITA and investigated the association between MHC class II transactivator polymorphism and expression of different MHC class II molecules in a large panel of melanoma cell lines obtained from the European Searchable Tumour Cell Line Database. Many cell lines showed no constitutive expression of HLA-DP, HLA-DQ and HLA-DR and no IFN-γ-induced increase in HLA class II surface expression. However, in some cases, IFN-γ treatment led to enhanced surface expression of HLA-DP and HLA-DR. HLA-DQ was less frequently expressed under basal conditions and was less frequently induced by IFN-γ. In these melanoma cell lines, constitutive surface expression of HLA-DR and HLA-DP was higher than that of HLA-DQ. In addition, high constitutive level of cell surface expression of HLA-DR was correlated with lower inducibility of this expression by IFN-γ. Finally, substitution A→G in the 5′ flanking region of CIITA promoter type III was associated with higher expression of constitutive HLA-DR (p<0.005). This study yielded a panel of melanoma cell lines with different patterns of constitutive and IFN-γ-induced expression of HLA class II that can be used in future studies of the mechanisms of regulation of HLA class II expression.

One-dimensional magnetopolymeric nanostructures with tailored sizes

Ultra-high aspect ratio nanofibers composed of poly(vinyl alcohol) and CoFe(2)O(4) nanoparticles (PVA/CoFe(2)O(4)) and moderate aspect ratio nanofibers composed of poly(vinyl chloride) and Fe(3)O(4) nanoparticles (PVC/Fe(3)O(4)) have been prepared. Magnetopolymeric one-dimensional (1D) nanostructures with any diameter and length can be prepared by template synthesis using anodic aluminum oxide (AAO) followed by the replication methods presented in this work. These replication methods are very effective, and allow the nanomoulding of any polymer-nanoparticle 1D composite. A first magnetic characterization of the nanostructured composites reveals a modest magnetic anisotropy. The development of magnetopolymeric nanofibers with adjusted length and diameter opens new opportunities in a wide range of applications.