Benzimidazolium Surfactants for Modification of Clays for Use with Styrenic Polymers

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays

Polymer - Xerogel Composites for Controlled Release Wound Dressings

Many polymers and composites have been used to prepare active wound dressings. These materials have typically exhibited potentially toxic burst release of the drugs within the first few hours followed by a much slower, potentially ineffective drug release rate thereafter. Many of these materials also degraded to produce inflammatory and cytotoxic products. To overcome these limitations, composite active wound dressings were prepared here from two fully biodegradable and tissue compatible components, silicon oxide sol–gel (xerogel) microparticles that were embedded in tyrosine-poly(ethylene glycol)-derived poly(ether carbonate) copolymer matrices. Sustained, controlled release of drugs from these composites was demonstrated in vitro using bupivacaine and mepivacaine, two water-soluble local anesthetics commonly used in clinical applications. By systematically varying independent compositional parameters of the composites, including the hydrophilic:hydrophobic balance of the tyrosine-derived monomers and poly(ethylene glycol) in the copolymers and the porosity, weight ratio and drug content of the xerogels, drug release kinetics approaching zero-order were obtained. Composites with xerogel mass fractions up to 75% and drug payloads as high as 13% by weight in the final material were fabricated without compromising the physical integrity or the controlled release kinetics. The copolymer–xerogel composites thus provided a unique solution for the sustained delivery of therapeutic agents from tissue compatible wound dressings

Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection

International audienceModern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technolog

High-throughput Method for Estimating the Time to Sustained Ignition of Polystyrene-Clay Nanocomposites Based on Thermogravimetric Analysis

Polymer-modified clay nanocomposites were prepared by melt blending and the time to ignition was measured by cone calorimetry at various heat fluxes. Based on these experimental results, a critical mass flux and critical percentage mass loss (pmlcrit) for piloted ignition were identified and validated for both virgin polystyrene and its composites, across a wide range of heating fluxes. Based on the assumption that the polymer degradation kinetics in the heating segment of the cone calorimetry (up to the moment of ignition) and thermogravimetry experiments are similar, and using the pmlcrit, we hypothesized that the onset degradation temperature of the TGA samples (defined here as the temperature at pmlcrit) could be used to estimate the time to sustained ignition in cone calorimetry experiments. The onset degradation temperature and the time to sustained ignition showed a good correlation, regardless of the heating flux used in cone calorimetry experiments

Thermal Degradation of Ethylene-Vinyl Acetate Copolymer Nanocomposites

The degradation pathway of ethylene–vinyl acetate copolymers and their nanocomposites is investigated using TGA/FT-IR, TGA, GC–MS, cone calorimetry and UV techniques to determine if the presence of the clay has an effect on the degradation pathway. The first step of the degradation, the loss of acetic acid by chain stripping, has been shown to be accelerated by the presence of clay. In this work we show that clay does affect the degradation pathway and that the presence of hydroxyl groups on the edges of the clay could be the cause of the accelerated initial step. The products of the second step of the degradation are changed in quantity and some new products are produced, showing that the clay also has an effect on this step of the degradation pathway. A scheme is suggested to account for the role of the clay in the degradation

The Relationship Between Thermal Degradation Behavior of Polymer and the Fire Retardancy of Polymer/Clay Nanocomposites

The change in the degradation pathway of a polymer by incorporation of clay has a significant effect on the fire retardancy of polymer/clay nanocomposites. Since the clay layers act as a barrier to mass transport and lead to superheated conditions in the condensed phase, extensive random scission of the products formed by radical recombination is an additional degradation pathway of polymers in the presence of clay. The polymers that show good fire retardancy upon nanocomposite formation exhibit significant intermolecular reactions, such as inter-chain aminolysis/acidolysis, radical recombination and hydrogen abstraction. In the case of the polymers that degrade through a radical pathway, the relative stability of the radical is the most important factor for the prediction of the effect that nanocomposite formation has on the reduction in the peak heat release rate. The more stable is the radical produced by the polymer, the better is the fire retardancy, as measured by the reduction in the peak heat release rate, of the polymer/clay nanocomposite

A Review of Recent Work in the Fire Retardancy of Nanocomposites

Recent work from this laboratory on various aspects of the fire retardancy of polymer-clay nanocomposites is reviewed. The principal areas of interest are: the amount of clay that is required, the mechanisms by which nanocomposite formation enhances fire retardancy, the role of the surfactant and synergy between conventional fire retardants and nanocomposite formation. This is used to set a pathway for the future of nanocomposites in fire retardancy

Thermal energy harvesting

et al.This chapter presents some recent advances in the field of thermal energy harvesting, starting with thermoelectric energy harvesting, with a focus on the prospects of materials nanostructuration. Research toward alternative solutions will also be presented. Thermoelectric (TE) conversion is the most straightforward method to convert thermal energy into electrical energy, able to power such systems as autonomous sensor networks. Raman thermometry offers particular advantages for a fast and contactless determination of the thermal conductivity. The highly porous Si material is nanostructured and has the properties of confined systems, including a very low thermal conductivity. The chapter explores an alternative route for thermal energy harvesting (TEH) with composites using the mechanical coupling between a thermal shape memory alloy (SMA) and a piezoelectric material.Peer Reviewe

Impact of the in situ rise in hydrogen partial pressure on graphene shape evolution during CVD growth of graphene

Exposing graphene to a hydrogen post-etching process yields dendritic graphene shapes. Here, we demonstrate that similar dendritic structures can be achieved at long growth times without adding hydrogen externally. These shapes are not a result of a surface diffusion controlled growth but of the competing backward reaction (etching), which dominates the growth dynamics at long times due to an in situ rise in the hydrogen partial pressure. We have performed a systematic study on the growth of graphene as a function of time to identify the onset and gradual evolution of graphene shapes caused by etching and then demonstrated that the etching can be stopped by reducing the flow of hydrogen from the feed. In addition, we have found that the etching rate due to the in situ rise in hydrogen is strongly dependent on the confinement (geometrical confinement) of copper foil. Highly etched graphene with dendritic shapes was observed in unconfined copper foil regions while no etching was found in graphene grown in a confined reaction region. This highlights the effect of the dynamic reactant distribution in activating the in situ etching process during growth, which needs to be counteracted or controlled for large scale growth.This research was partially supported by the Spanish Ministry of Economy and Competitiveness, MINECO (under Contracts No. MAT2013-46785-P, No. MAT2016-75952-R, No. MAT2015-68307- P and Severo Ochoa No. SEV-2013-0295), by the European Research Council under Grant Agreement No. 306652 SPINBOUND, by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 696656, and by the CERCA Programme and the Secretariat for Universities and Research, Knowledge Department of the Generalitat de Catalunya 2014 SGR 56. ZMG acknowledges support from MINECO FPI fellowship under Contract No. BES-2014-069925.Peer reviewe

Electrical detection of spin precession in freely suspended graphene spin valves on cross-linked poly(methyl methacrylate)

Spin injection and detection is achieved in freely suspended graphene using cobalt electrodes and a nonlocal spin-valve geometry. The devices are fabricated with a single electron-beam-resist poly(methyl methacrylate) process that minimizes both the fabrication steps and the number of (aggressive) chemicals used, greatly reducing contamination and increasing the yield of high-quality, mechanically stable devices. As-grown devices can present mobilities exceeding 104 cm2 V-1 s-1 at room temperature and, because the contacts deposited on graphene are only exposed to acetone and isopropanol, the method is compatible with almost any contacting material. Spin accumulation and spin precession are studied in these nonlocal spin valves. Fitting of Hanle spin precession data in bilayer and multilayer graphene yields a spin relaxation time of ~125-250 ps and a spin diffusion length of 1.7-1.9 ¿m at room temperature. Electrical detection of spin precession in freely suspended graphene spin valves. The devices are fabricated with a single electron-beam-resist poly(methyl methacrylate) process that minimizes both the fabrication steps and the number of (aggressive) chemicals used, reducing contamination and increasing the yield of the high-quality devices. The method is compatible with almost any contacting material. As-grown devices can present mobilities exceeding 104 cm2 V-1 s-1 at room temperature. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This research was partially supported by the Spanish Ministry of Science and Innovation, MICINN (MAT2010-18065 and FIS2009-10150). J.V.d.V acknowledges support from FWO-Vl.Peer Reviewe