Amelia Linares

Confinement-Induced One-Dimensional Ferroelectric Polymer Arrays

This work demonstrates the use of wetting nanoporous alumina template with polymer solution to produce arrays of isolated poly(vinylidene fluoride) (PVDF) ferroelectric gamma-type nanorods supported within a nonpolar alpha-structure film. The method is based upon a crystal phase transition which occurs due to PVDF confinement within alumina nanoporous. The system was studied using scanning X-ray microdiffraction (micro-XRD) that allows the solid-solid phase transition from the alpha-nonpolar crystal form (bulk) to the gamma polar ferroelectric form (nanorod array) to be spatially resolved, as well as providing crystallinity and orientation information. The results reveal that the interaction between polymer chains and the porous membranes walls imposes a flat-on lamella growth along the nanorrods long axis, while improving crystal orientation.

Understanding crystallization features of P(VDF-TrFE) copolymers under confinement to optimize ferroelectricity in nanostructures

The successful development of ferroelectric polymer devices depends on the effective fabrication of polar ferroelectric crystalline nanostructures. We demonstrate, by scanning X-ray microdiffraction using synchrotron light, the heterogeneous character of high aspect ratio one-dimensional nanoarrays of poly(vinylidene fluoride-co-trifluoroethylene) copolymers supported by a residual polymer film. They were prepared by melt and solution template wetting, using porous anodic aluminum oxide as a template. The spatial evolution of different polymorphs from the mixture of paraelectric and ferroelectric crystal forms (residual film) to the pure ferroelectric form (nanoarray) is evidenced for the samples prepared by solution wetting. However, for samples prepared by melt wetting the ferroelectric phase is exclusively obtained in both the residual film and nanoarray. The crystal nuclei formed in the polymer film connected to the nanoarray play a key role in determining the formation of a crystallinity distribution gradient, where the crystallinity decreases along the first 5-10 microns in the nanorods reaching a steady value afterwards. The minimum decrease in crystallinity is revealed for samples prepared by melt wetting. The results reported in this work endeavour to enhance the understanding of crystallization under confinement for ferroelectric copolymers and reveal the parameters for improving the ferroelectric character of polymer nanostructures.

Crystallization under One-Dimensional Confinement in Alumina Nanopores of Poly(trimethylene terephthalate) and Its Composites with Single Wall Carbon Nanotubes

We report the preparation of semicrystalline polymer nanorods of PTT and of its nanocomposites with SWCNTs by infiltration of the molten polymer into disordered anodic alumina membranes. An accurate study of the crystalline orientation of these systems has been accomplished by means of X-ray microdiffraction. While polymer residual film exhibits isotropic character, edge-on lamellae are formed upon approaching the polymer/membrane interface. This effect might be due to the elongational flow that takes place in the molten state as polymer chains infiltrate the AAO membrane. At the interface, edge-on and flat-on crystalline lamellae coexist as a consequence of the strong interaction between the polymer and the AAO surface. Inside the nanopores, the confined environment induces a kinetic selection of polymer crystals which only allows the growth of crystalline lamellae with its a-axis parallel to that of the pore. In the case of PTT/SWCNT nanocomposites, this effect, in conjunction with the strong interaction between polymer and AAO surface, seems to prevail over the templating effect of the carbon nanotubes and a similar orientation to that of the neat PTT case is observed.

The effect of interfacial adhesion and morphology on the mechanical properties of polypropylene composites containing different acid surface treated sepiolites

The study of the microstructure of polymeric composites and its relationship to mechanical properties, are of great importance. In the present study vv8 have carried out a study of the microstructure of polymeric composites of polypropylene and different sepiolites treated with organic acids, in order to determine the mesophase produced around We filler particles and its relationship with the mechanical properties of the composites. This study was made using scanning electron microscopy, differential Scanning calorimetry and mechanical tests.

Characterization of polymer systems based on sulfonated poly(2,6-dimethyl-1,4-phenylene oxide)

The sulfonation reaction of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been carried out, incorporating the resulting product into pure PPO to study, in forthcoming research, the electrical and mechanical features of the composites with regard to their performance in fuel cells. Pure sulfonated polymers and their blends have been characterized from a microstructural and electrical point of view, by means of X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and complex impedance spectroscopy. Membranes have been manufactured with excellent ionic conductivity at room temperature. © 2000 Society of Chemical Industry

Applications of a statistical model to the analysis of the kinetic parameters in isothermal and non-isothermal crystallization of polymer blends based on PVDF

In this work the classical Scheffe model is applied to the study of isothermal and non-isothermal crystallization of blends based on the systems PVDF, PMMA and PVA. In the light of the results obtained the validity of the model proposed is assessed. The authors endeavour to contribute to the discussion on the compatibility of these materials, which latter aspect is of utmost relevance when interpreting the properties presented by these polymer blends.

Electrical and morphological studies of polymeric composites based on carbon black

Conventional polymers, polypropylene and polystyrene, containing carbon black as conductor additive, were prepared. Impedance complex-plane analysis is used in order to characterize the composites obtained. Microstructure studies indicate that carbon black affects the size but not the geometrical morphology. The electrical conductivity of polypropylene composites is higher than polystyrene, and is correlated to the microstructural and wettability properties of these polymer matrices.

On the electrical conductivity of PVDF composites with different carbon-based nanoadditives

Composites based on poly(vinylidene fluoride) (PVDF) and different carbon additives, such as carbon nanofibers (CNF), graphite (G), expanded graphite (EG), and single-walled carbon nanotubes (SWCNT) have been prepared by nonsolvent precipitation, from solution, and subsequent melt processing. From a structural point of view, the α-crystal phase is the predominant crystal form in all the nanocomposites. However, those containing CNF, G, and EG at high nanoadditive content present also β-crystal phase. Even though the intrinsic thermal properties of PVDF are hardly affected, the nanoadditives act as nucleating agents for the crystallization. In regard to the electrical properties, all nanocomposites exhibit a percolating behavior. Moreover, the fact that the nanocomposites present both high dc conductivity and high dielectric constant, in a certain nanoadditive concentration range below the percolation threshold, suggests that a tunneling conduction mechanism for charge transport is present. With regard to the ac electrical properties, depending on the morphology of the different additives, the charge transport above percolation threshold can be explained taking into account the anomalous diffusion effect for high nanoadditive content or an intercluster polarization mechanism when the nanoadditive concentration decreases.

Heterogeneous sulfonation of blend systems based on hydrogenated poly(butadiene-styrene) block copolymer. Electrical and structural characterization

Abstract Conducting membranes of hydrogenated poly(butadiene–styrene) block copolymer (HPBS) were obtained by heterogeneous sulfonation and then their electrical properties were studied. In addition, the effects of PP content on the morphology of these blends, as well as their conducting properties, were considered. The degree of sulfonation was determined by means of photoelectron spectroscopy (XPS) and the structural characterization was carried out using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). The results show that sulfonated HPBS has difficulties to be made into membranes besides reduced conductivity while the polymer blends with PP have high conductivity values and good dimensional stability. In this work, we find that increasing the PP content in the blend improves mechanical aspects, but on the other hand, conductivity decreases as the PP does not participate in the sulfonation process. The sample of composition 70% HPBS/30% PP sulfonated for 12 h with HClSO3 0.1 M (AMP-13S) was seen to be adequate as fuel cell membrane, especially due to the high conductivity properties and excellent dimensional stability.

Dynamic mechanical properties of binary and ternary blends based on PVDF

SummaryA universally accepted criterion when assessing blend compatibility is the existence of a single glass transition temperature, which changes as a function of blend composition. Differential scanning calorimetry and dynamic mechanical strain spectra are powerful tools in the study of polymer relaxation in the glass transition zone. In this research both techniques are employed to determine the glass transition temperatures of a series of polymer blends based on polyvinylidene fluoride. In the light of the data obtained further thought is given to the discrepancies between the results obtained with one and the other method, as well as to the compatibility of the experimental blends.