https://iopscience.iop.org/article/10.1088/2053-1591/ab68a0/pdf

Optical properties of transparent PMMA-PS/ZnO NPs polymeric nanocomposite films: UV-Shielding applications

A series of high dielectric composite films based on low-cost and eco-friendly titanium dioxide (TiO2) and cellulose nanofibril (CNF) was prepared under a facile condition. The relative dielectric constants (er) and dielectric loss (
 $$ \tan\updelta $$
 ) were studied as the function of frequency and filler content. The er of CNF/TiO2 composite film was 19.51 (at 1 kHz) with a relatively low dielectric loss. Compared with pure CNF films (er = 6.92 at 1 kHz), the er of the composite film was improved about three times with the dielectric loss increased slightly. The effects of TiO2 addition and hot-press treatment on microstructure, thermal stability, and dynamic mechanical properties of the composite films were also analyzed. It was found that the addition of TiO2 particles reduces the cellulose–cellulose bonding so generates more pores in the films, which has significant impacts on both dielectric and physical strength properties.

Facile preparation of high dielectric flexible films based on titanium dioxide and cellulose nanofibrils

The processes of molecular relaxation in the binary nitrate–perchlorate solid systems LiNO3–LiClO4, NaNO3–NaClO4, and KNO3–KClO4 have been investigated using Raman spectroscopy. It has been found that the relaxation time of the ν1(A) vibration of the NO3- anion in the binary solid system is shorter than that in the pure metal nitrates. It has been shown that an increase in the relaxation rate is caused by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is associated with the excitation of a vibration of another anion (ClO4-), as well as with the “creation” of a lattice phonon. It has been established that the condition for the realization of the relaxation mechanism is that the difference between the frequencies of the aforementioned vibrations should correspond to the range of sufficiently high densities of states of the phonon spectrum.

Inelastic intermolecular exchange of vibrational quanta and relaxation of vibrationally excited states in binary solid systems

This paper reports on a comparative study of phase transitions in nanocomposites made up of KNO3 embedded in 10-μm-thick MCM-41 films with unidirectional pores 4.0 nm in size on an aluminum substrate and of nanocomposites prepared in the form of potassium-nitrate-filled pressed MCM-41 powders with 3.7-nm pores. The temperature dependences of linear permittivity and the amplitude of third harmonic generation have been measured under heating and cooling. The structural transition from phase II to phase I shifts under heating relative to that occurring in bulk KNO3 toward lower temperatures for potassium nitrate in the film and toward higher temperatures for the pressed MCM-41-based nanocomposite. A significant difference has been observed also within the region of existence of ferroelectric phase III. The data obtained suggest that the shifts of phase transition temperatures observed in the conditions of nanoconfinement are influenced markedly not only by pore size and geometry but also by other factors.

Phase transitions in KNO 3 embedded in MCM-41 films with regular nanopores

Nanostructured composite materials containing both magnetic (Fe3O4) and ferroelectric (γ-KNO3) phases have been synthesized based on ferromagnetic iron-containing porous silicate glass. The nanocomposite structure has been investigated using the methods of transmission electron microscopy and X-ray diffraction analysis. The composites electrical resistivity in the temperature range 298–490 K has been studied as well.

New vitreous nanocomposites containing phases of Fe3O4 and γ-KNO3

The temperature dependences of the linear dielectric permittivity, the third harmonic amplitude, and the heat capacity of nanoporous silica matrices MCM-41 with cellular channels (3.7 and 2.6 nm in diameter) filled with KNO3 have been investigated in comparison with those obtained for bulk potassium nitrate. Measurements have been performed during heating and cooling in the range from room temperature to 463 K. Anomalies corresponding to structural phase transitions have been observed. A significant broadening of the temperature region of the existence of the ferroelectric phase III of potassium nitrate upon cooling has been revealed. This broadening increases with a decrease in the size of pores. It has been shown that, in the nanocomposites with potassium nitrate, the ferroelectric phase can also be formed during heating. The efficiency of observation of the third harmonic generation for studying nanocomposites with the ferroelectric phase has been demonstrated.

Dielectric and calorimetric investigations of KNO 3 in pores of nanoporous silica matrices MCM-41

We present the results of studies of the dielectric properties of nanocomposites based on Al2O3 oxide films with a pore size of 330 and 60 nm with particles of an organic ferroelectric diisopropylammonium bromide (C6H16BrN, DIPAB) introduced into the pores, aimed at determining the size dependences of phase transition parameters. A shift in the phase transition to low temperatures and diffusion of the transition are found, which become more significant for smaller pores. A broadening of the temperature hysteresis of the dielectric constant of nanocomposites during the phase transition was also observed. The decrease in the phase transition temperature in nanocomposites with DIPAB nanoparticles is consistent with theoretical models of the size effects on the structural phase transition.

Size Effect in Nanocomposites Based on Molecular Ferroelectric Diisopropylammonium Bromide

Temperature dependences of the linear permittivity e' and the third harmonic amplitude γ3ω of composites prepared by introducing ferroelectrics SC(NH2)2 into matrices of porous aluminum oxide Al2O3 with pore sizes 60 and 100 nm are determined. It is found that temperature T
 c
 of the ferroelectric phase transition and the temperature T
 i
 of the phase transition from incommensurable phase to the paraphrase increase significantly. The transition shifts increase as pore diameters decrease.

Phase transitions of SC(NH 2 ) 2 ferroelectrics in Al 2 O 3 -based nanoporous matrices

Variations with temperature of the linear dielectric permittivity and amplitude of the third harmonic were studied for nanoporous MCM-41 matrices with 4.0-nm channel pores filled with the (NH4)2SO4 ferroelectric, in comparison with bulk ammonium sulfate. The measurements were performed upon heating and cooling in the temperature range from 100 K to room temperature. A noticeable shift to low temperatures (by approximately 25 K) for the ferroelectric phase transition in the MCM-41/(NH4)2SO4 nanocomposite as compared to bulk (NH4)2SO4 was revealed. The temperature hysteresis observed at the phase transition in the nanocomposite was approximately 2 K which is close to that in bulk ammonium sulfate. The significant decrease of the transition temperature in nanostructured ammonium sulfate agrees with the theoretical predictions based on the Landau and Ising models of the size effect on the ferroelectric phase transition in isolated small particles.

Dielectric properties of the nanoporous MCM-41 matrix filled with the (NH4)2SO4 ferroelectric

Linear and non-linear dielectric properties of composites based on KIO3 and nanocrystalline cellulose Acetobacter Xylinum were investigated. An increase in temperatures of the structural transition...

A. Yu. Milinskii

Papers

Dielectric and calorimetric investigations of KNO 3 in pores of nanoporous silica matrices MCM-41

Size Effect in Nanocomposites Based on Molecular Ferroelectric Diisopropylammonium Bromide

Phase transitions of SC(NH 2 ) 2 ferroelectrics in Al 2 O 3 -based nanoporous matrices

Dielectric properties of the nanoporous MCM-41 matrix filled with the (NH4)2SO4 ferroelectric

Dielectric properties of nanocomposites based on potassium iodate with porous nanocrystalline cellulose