No abstract

No abstract

No abstract

The dielectric characteristics of various modified montmorillonites suspensions in polydimethylsiloxane were investigated. Such materials are promising candidates as electrorheological fluids. The effect of small water content and temperature change in the dielectric spectra of suspensions was studied. The electrical conductivity of suspensions rises with filler concentration. Conductivity also increases with frequency for all samples by 5-6 orders of magnitude. The frequency dependence of permittivity changes significantly with temperature and strongly depends on the type of modifier. The positions of relaxation transitions peaks observed in dielectric loss curves substantially depend on the type of filler and water content. Dielectric loss peaks shift to higher frequencies with temperature. Relaxation mechanism is related to filler and described by capacitor model. Based on X-ray data a model of relaxation transitions is proposed. Also, the activation energy of dielectric relaxation is estimated. The activation energy is independent of filler concentration but is determined by the structural features of fillers in polymer medium. The prospects of dielectric spectroscopy for analyzing the layered nanosilicates structure in polymer solution are demonstrated. V C 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46614.

An experimental study of molecular hydrogen adsorption on single gold nanoparticles of various sizes deposited on the surface of highly oriented pyrolytic graphite (HOPG) was carried out by means of scanning tunneling microscopy and spectroscopy. The effect of size on the HOPG/Au system was established. Hydrogen was dissociatively chemisorbed on the surface of gold nanoparticles with an average size of 5–6 nanometers. An increase in the size of nanoparticles to 10 nm or more led to hydrogen chemisorption being inhibited and unable to be detected.

No abstract

The adsorption of CO on the surface of Cu-based nanoparticles was studied in the presence of an external electric field by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Nanoparticles were synthesized on the surface of a graphite support by the impregnation–precipitation method. The chemical composition of the surface of the nanoparticles was determined as a mixture of Cu2O, Cu4O3 and CuO oxides. CO was adsorbed from the gas phase onto the surface of the nanoparticles. During the adsorption process, the potential differences ΔV = +1 or −1 V were applied to the vacuum gap between the sample and the grounded tip. Thus, the system of the STM tip and sample surface formed an asymmetric capacitor, inside which an inhomogeneous electric field existed. The CO adsorption process is accompanied by the partial reduction of nanoparticles. Due to the orientation of the CO molecule in the electric field, the reduction was weak in the case of a positive potential difference, while in the case of a negative potential difference, the reduction rate increased significantly. The ability to control the adsorption process of CO by means of an external electric field was demonstrated. The size of the nanoparticle was shown to be the key factor affecting the adsorption process, and particularly, the strength of the local electric field close to the nanoparticle surface.

In this study, wide-angle X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy were employed to address the crystalline structure and morphology of poly(p-xylylene)−PbS nanocomposite thin films prepared by vapor deposition polymerization as well as their evolution upon thermal annealing. It was found that as-synthesized samples with different PbS contents demonstrate similar diffraction patterns that cannot be fully ascribed to a decrease in crystallite size, indicating distorted crystal structure of PbS nanoparticles compared to the bulk PbS. X-ray absorption spectroscopy reveals wide distribution of Pb−S bond lengths with a minimum value of 2.67 Å, which can be attributed to the presence of molecular (PbS) n clusters in the studied films. It was shown that thermal annealing can be used to control the size of PbS nanoparticles and, as a consequence, optical properties of the composite films. The UV−vis absorption spectra demonstrate pronounced red shift of the absorption edge correlated with the growth of PbS nanoparticles upon annealing. Comprehensive analysis of several theoretical models describing the effect of nanoparticles size on optical band gap of the composite material has been performed and compared with the experimental data.