J.J. del Val

Bio: J.J. del Val is an academic researcher from University of the Basque Country. The author has contributed to research in topics: Coercivity & Amorphous solid. The author has an hindex of 14, co-authored 88 publications receiving 858 citations. Previous affiliations of J.J. del Val include Spanish National Research Council.

Study of the α and β relaxations on a commercial poly(vinyl chloride) by thermally stimulated creep and depolarization current techniques

Abstract: Thermally stimulated creep and depolarization current measurements have been carried out in a temperature range between −180 and 120 °C, on a pure commercial poly(vinyl chloride). Mechanical and dielectric relaxation times involved in α and β relaxations are obtained by fractional stresses/polarizations procedure. The distribution of the Arrhenius‐like kinetic parameters, deduced from the relaxation times, is interpreted in terms of compensation laws. From the obtained results, a same molecular origin can be assumed for the mechanical and dielectric behavior in both α and β relaxations. Moreover, the compensation law analysis leads to two different relaxations modes, likely associated to two kinds of thermally activated molecular motions, in β relaxation. In the α region, the values of found kinetic parameters point out a high degree of cooperativeness of the involved molecular motions. Depolarization curve in this region shows a high temperature peak, not found in the mechanical one, whose evolution with the poling field allows us to assign it to a nondipolar process associated to the movement of free charge carriers.

CoFe2O4–polypyrrole (PPy) nanocomposites: new multifunctional materials

Abstract: Spinel ferrites (iron cobalt oxide) were prepared by the microemulsion method at different temperatures and sodium dodecyl sulphate (SDS) surfactant concentrations. Subsequently, a quantity of the different samples were coated with an intrinsically conducting polymer (ICP) shell of polypyrrole. The polymer shell was synthesized by a chemical route after the ferrites particle production. By combining in a single material the electrical conductivity of ICPs and the magnetic properties of nanopowder ferrites, new multifunctional materials have been developed. Different CoFe2O4 grain size particles were obtained ranging from 3 to 30 nm, as determined by x-ray diffraction (XRD). Particles with grain size below a critical size exhibit a superparamagnetic behaviour. These superparamagnetic particles, without and with a conducting polymer shell, were analysed by transmission electron microscopy (TEM) to find the grains' morphology and the growth evolution of the polypyrrole shell in the ferrites grains. The electrical conductivity of the nanocomposite was measured by the four points probe method, showing values of 120 ± 4 S cm−1 at ambient temperature. The behaviour of the magnetization and the coercivity with temperature, from nearly 0 K to the ambient, were measured in a vibrating sample magnetometer (VSM).

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide

Abstract: Significant concerns have been raised over pollution of antibiotics including tetracyclines in aquatic environments in recent years. Graphene oxide (GO) is a potential effective absorbent for tetracycline antibiotics and can be used to remove them from aqueous solution. Tetracycline strongly deposited on the GO surface via π-π interaction and cation-π bonding. The adsorption isotherm fits Langmuir and Temkin models well, and the theoretical maximum of adsorption capacity calculated by Langmuir model is 313 mg g(-1), which is approximately in a close agreement with the measured data. The kinetics of adsorption fits pseudo-second-order model perfectly, and it has a better rate constant of sorption (k), 0.065 g mg(-1) h(-1), than other adsorbents. The adsorption capacities of tetracycline on GO decreased with the increase in pH or Na(+) concentration. The adsorption isotherms of oxytetracycline and doxycycline on GO were discussed and compared.

Graphene filled polymer nanocomposites

Abstract: Graphene has attracted the attention of a growing number of scientists from several disciplines due to its remarkable physical properties and chemical functionalisation capabilities. This review presents an overview of graphene/polymer nanocomposites discussing preparation, properties and potential applications. The challenges and outlook of these emerging polymer nanocomposites are also discussed.

Strategies for chemical modification of graphene and applications of chemically modified graphene

Abstract: Graphene's unique thermal, electric and mechanical properties originate from its structure, including being single-atom thick, two-dimensional and extensively conjugated. These structural elements endow graphene with advantageous thermal, electric and mechanical properties. However, the application of graphene is challenged by issues of production, storage and processing. Therefore, the stabilization and modification of graphene have attracted extensive interest. In this review we summarize the strategies for chemical modification of graphene, the influence of modification and the applications in various areas. Generally speaking, chemical modification can be achieved via either covalent or non-covalent interactions. Covalent modifications often destroy some of the graphene conjugation system, resulting in compromising some of its properties. Therefore, in this review we focus mainly on the non-covalent modification methodologies, e.g. π–π stacking interactions and van der Waals force, because the non-covalent modifications are believed to preserve the natural structure and properties. We also discuss the challenges associated with the production, processing and performance enhancement. Future perspectives for production of graphene in large size with fewer defects and under milder conditions are discussed along with the manipulation of graphene's electric, mechanical and other properties.