Annotation of the results obtained in 2021
As part of the third stage of the work, the dielectric properties of three-phase composites of optimal compositions, selected based on the results of studies at previous stages and on the basis of high scientific and practical interest in epoxy resin (ER), were studied. The dielectric properties of three-phase composites were studied in comparison with a pure polymer matrix. An increase in the permittivity in three-phase composites is achieved, first of all, due to the addition of a ceramic filler, whose function in the system under study is performed by hollandites of various compositions. Polarization processes in such materials are due to the mobility of K+ ions in the quasi-one-dimensional channels of the tunnel structure, which is accompanied by the redistribution of electrons in the structural lattice due to the variable valence of titanium and transition metal (Ni, Fe, Cu) in the composition of hollandite. The typical morphology of particles of hollandite-like materials is columnar, which hinders charge transfer and requires the use of conductive particles, which are carbon of various modifications. For all polymer matrices, the permittivity is determined by the qualitative and quantitative composition of the fillers and is predominantly independent of frequency, except for composites with a high concentration of heterostructural nanoceramics and a carbon additive, which are characterized by an increase in ε with decreasing frequency. The frequency dependences of the dielectric loss tangent for three-phase composites of all studied compositions have a similar behavior with maxima and minima at certain frequencies associated with relaxation processes in the materials. For the PMMA matrix, an increase in the permittivity from 5 for a pure matrix to 40 units for three-phase composites was achieved at a loss tangent below 0.1. In the case of PVDF, an increase in the dielectric constant from 5 for PVDF to 25 for three-phase composites based on it was obtained, while the dielectric loss tangent also mainly does not increase above 0.1. Polymer matrix three-phase composites based on epoxy resin of optimal composition are characterized by an increase in ε from 5 for pure epoxy resin to 25 at tanδ ~ 0.1. In the production of three-phase polymer matrix composites with the simultaneous use of ceramic and conductive fillers, a synergistic effect is found, which in this study was evaluated by comparing the change in ε and tan δ for the polymer matrix after adding fillers singly and together. An impedance study of three-phase composites shows that the analysis of impedance data using a classical RC network is not effective, therefore, as in many literature sources, a constant phase element (CPE) is used instead of a capacitive element (C). This analytical approach can be used to characterize polymer matrix composites with various ceramic fillers. For PVDF-KFTO 30%+CNT 0.5-1.5% samples, the impedance is interpreted as a circuit with three elements: R, C and CPE. In this case, R can be attributed to the volume resistance at direct current, C is the geometric capacitance, and the CPE element describes the charge transfer along the conductive carbon regions. In this case, the exponent n takes values about 0.5, which can be interpreted as a diffusion impedance and, apparently, is associated with local barriers in the conductive network of carbon regions, including the tunneling effect. The described behavior is characteristic of polymer-matrix composites with fillers in the form of heterostructural nanoceramics of composition Kx(Ti,Me)yOz (Me = Fe, Ni, Cu) and various modifications of carbon. The formation of single-layer and multilayer functional coatings of selected compositions of composites when applied to ITO glass, ITO-coated polymer films and steel plates was carried out by the "spin-coating" and "doctor blade" methods. Depending on the coating formation method used, the polymer matrix and the quantitative ratio of components, as well as the conditions for applying materials to the substrate, coatings differ in uniformity and thickness. Depending on the rotation of the substrate in the "spin-coating" method and the gap between the knife and the plane of the substrate in the case of the "doctor blade" method, the thickness of the coatings varied from 10 to 100 µm. To study the dielectric properties of three-phase composites of selected compositions during bending at various angles, the "doctor blade" method was used to obtain functional coatings on a PET film with an electrically conductive ITO coating. It has been established that all studied dielectric properties (permittivity, dielectric loss tangent, conductivity) of three-phase composites of optimal compositions differ by no more than 2.5% at bending up to 90°. The dielectric strength of optimal combinations of polymer matrix/heterostructural nanoceramic (Kx(Ti,Me)yOz)/nanocarbon modification was measured by fixing the breakdown voltage, with the sample placed between two steel electrodes, between which the voltage increased uniformly at a rate of 500 V/s. The electrical strength was calculated as the ratio of the breakdown voltage to the sample thickness. For the PMMA matrix, the expected dielectric strength was 300 kV/mm; for PVDF – 20-25 kV/mm; for epoxy resin – 16 kV/mm; for fluoroplast – 50-80 kV/mm. At the same time, composites filled with 30 vol.% hollandite have an electrical strength an order of magnitude lower than a pure polymer matrix. An increase in the proportion of the carbon component of the three-phase composite contributes to a further decrease in electrical strength. The results of the research are analyzed in three stages, and a comparison is made with the requirements for materials used in the manufacture of electronics elements. Recommendations have been prepared on scaling the methods and technology for the synthesis of composites. Taking into account the intensive development of 5G technologies, as well as the growth trends in the production of flexible electronics, the developed approaches for the manufacture of three-phase composites can be used in the design of elements of the electronic component base. In this case, for the manufacture of thin films, it is recommended to use the calendering method and fluoroplastic dispersions as a polymer matrix. The use of epoxy resin and PMMA matrices is recommended for the manufacture of elements of complex geometric shapes. The use of a PVDF matrix using anti-solvent deposition technology makes it possible to control the content of α-, β-, γ-phases, which increases manufacturability in the industrial production of elements of the electronic component of the base and other electrical products. 2 articles in journals: Polymers (Q1) and Russian Journal of Applied Chemistry (RSCI) were published.

 

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Annotation of the results obtained in 2019
During the first year of the research, heterostructured ceramic materials of various compositions Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Cu, Mn) were synthesized using a unique solution technology by modifying potassium polytitanate with transition metal compounds in aqueous solutions of the corresponding sulfates under experimentally selected conditions (concentration and pH of the modifying solution), which, upon subsequent heat treatment, crystallize single-phase ceramics with a hollandite structure. The frequency dependences of the conductivity of all samples are characterized by an increase in conductivity with increasing frequency, which is associated with the presence of a hopping charge transfer mechanism. For Kx(Ti, Me)yOz (Me = Cu) sample the conductivity is in the range from 3E-04 to 1E-06 S / cm, for the Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Mn) from 1E-05 to 1E-08 S / cm. The dielectric loss tangent for heterostructured nanoceramics of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Cu, Mn) in the frequency range of 1 MHz - 300 Hz has a maximum peak corresponding to the relaxation process of heterophase polarization and lies in the range of 1E03 - 5Е05 Hz. In this case, the dielectric loss tangent has values ​​from 0.01 to 3 at the maximum. The permittivity of the studied heterostructured nanoceramics of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Cu, Mn) increases with decreasing frequency. The frequency behavior of the studied ceramics is explained by the contribution of polarization inside the grain (in the literature - the electron-pinned defect-dipole, EPDD model) at frequencies of MHz, at frequencies 1E05-1E03 the contribution of the grain boundary capacitance (in the literature - the internal barrier layer capacitance, IBLC model) and at frequencies below 1E03 the contribution of the electrode polarization. The permittivity values ​​for the heterostructured nanoceramics of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Cu, Mn) in the frequency range 1 MHz - 300 Hz are 75-250 for 1 MHz and 1E03-2E04 for 300 Hz. The values ​​of the permittivity of heterostructured nanoceramics of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Co, Cr, Cu, Mn) in the frequency range 8 GHz - 11 GHz have values ​​from 4.5 for Me = Ni to 8.4 for Me = Cu. The dielectric loss tangent in the frequency range of 8 GHz - 11 GHz is in the range of 0.05-0.2. The most promising polymer matrices in terms of dielectric properties and technological characteristics were selected and various methods for creating polymer-matrix composites with a ceramic filler content that varied over a wide range were worked out. Composites with 20-50 vol% nanoceramic filler are characterized by a significant increase in ε 'at f <10Е04 Hz. The dispersion of the permittivity on the ε'-f curves for composites with a high hollandite content is related to polarization processes in ceramic ferroelectric, such as the electron density shift in accordance with the Ti4+ + e ↔ Ti3+ and Ме3+ +e ↔ Мe2+ schemes, accompanied by local motion of K+ ions in channels of a hollandite-like structure. Percolation thresholds were calculated for the frequencies 300 Hz, 10 kHz, 1 MHz, and 11 GHz for the PMMA-Kx(Ti, Me)yOz (Me = Co, Cr) and FT-Kx(Ti, Me) yOz (Me = Co, Fe) systems. Based on impedance studies at various frequencies and temperatures, systems of greatest interest for further studies have been identified. At a relatively low filler content (≤20 vol.%), an increase in the concentration of heterostructured nanoceramics contributes to an increase in the temperature coefficient of the permittivity, probably due to the increased contact surface area of ​​polymer-heterostructured nanoceramics and polarization at the phase boundary. Under these conditions, the filler particles are isolated by a polymer matrix, and the resulting composites have low porosity. However, composites containing 20 vol.% of the filler are characterized by a sharply reduced value of εεr, this phenomenon is associated with the percolation effect. An increase in heterostructured nanoceramics to 30 vol.% contributes to the production of composites in which some filler particles have direct contact. This structural transformation reduces the contribution of the phase polarization of polymer-heterostructured nanoceramics; as a result, after reaching the percolation threshold, an increase in temperature leads to an increase in the mobility of charge carriers in agglomerated filler particles, which leads to a decrease in the permittivity with an increase in the number of heterostructured nanoceramics. A subsequent increase in the ceramic filler supports an increase in the permittivity, as well as an increase in τεr. Temperature coefficients range from -120 ppm / ° C PMMA-Kx (Ti, Me) yOz (Me = Cr) 20 vol.% (11 GHz) to 600 FT-Kx (Ti, Me) yOz (Me = Co) 20 rpm .% (300 GHz). Thus, the studied composites can be considered as promising dielectric materials due to the high permittivity, as well as relatively low and acceptable dielectric losses. It is important that the manufacture of such materials does not include complex technological operations associated with the modification of the surface of the filler particles. According to the research, an article by Gorshkov N.V., Goffman V.G., Vikulova M.A., Burmistrov I.N., Sleptsov V.V., Gorokhovsky A.V. Polytetrafluorethylene-based high-k composites with low dielectric loss filled with priderite (K1.46Ti7.2Fe0.8O16) Journal of Applied Polymer Science (Q1) was published.

 

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Annotation of the results obtained in 2020
During the second year of work on the project, special attention was paid to determining the optimal system of three-phase composites for further investigation of the dependence of functional properties on variable factors. As the main mechanical property of interest for synthesized composites based on polymer matrices PMMA and fluoroplastic, the stress of forced elasticity was investigated at a deformation value of 1%. The test results showed an increase in the forced elasticity stress upon the addition of a filler in the form of a heterostructured nanoceramic of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Cu) relative to a pure polymer matrix up to 14% for PMMA and up to 25% for fluoroplastic. In this case, the type of modifying metal in the composition of the heterostructure nanoceramics does not affect the mechanical properties of the composites. The choice of PMMA as a polymer matrix obtained by the solution method and fluoroplastic as a polymer matrix obtained by the dispersed method is due to both the individual dielectric characteristics of the material and the nature of the interaction with heterostructure nanoceramics of the composition Kx(Ti, Me)yOz (Me = Fe, Ni, Cu) when obtaining composites (without chemical and structural transformations). The most common nanocarbon modifications used in the formation of composite materials with ceramics of various compositions are carbon black, carbon nanotubes, and oxygraphene. Additionally, a large number of scientific studies are devoted to the production of core-shell coatings by processing powders of simple and complex oxides in a dopamine solution. The possibility of comparison with the literature data and the establishment of the peculiarities of the influence of these carbon sources on the properties of the heterostructural nanoceramics considered in the framework of the project determined their choice for modifying the surface of hollandites. Of the known approaches to the preparation of ceramic / carbon composite materials, the powder method in two variations (high-energy grinding and dispersion in suspensions), as well as treatment in a solution of an organic carbon source (using dopamine) with an obligatory final stage in the form of annealing in an inert atmosphere (argon). The use of surfactants of various chemical nature: cationic (cetyltrimethylammonium bromide) and anionic (lauryl sulfate) to prevent or reduce the process of stratification of carbon with hollandite did not give significant improvements, which made it possible to make a decision - not to complicate the technology of manufacturing three-phase composites and to use previously developed techniques for two-phase composites. The production of a carbon coating, as well as the formation of heterostructured nanoceramic / carbon material composites, is confirmed by a change in the FTIR transmission spectra relative to the spectrum of the initial ceramic sample. First of all, attention is drawn to the shift of the reflection responsible for the vibration of the Ti-O-Ti bond (~ 520 cm-1) to the region of lower wavenumbers (~ 490 cm-1), which indicates the formation of a Ti-O-C bond. The FTIR transmission spectra of three-phase composites show several characteristic absorption bands related to the vibrations of the functional groups of the filler and matrix. It should be noted that the addition of a carbon material to the composition of the heterostructured nanoceramic does not lead to the appearance of reflections that significantly change the character of the spectra. In this case, it is necessary to note a consistent increase in the intensity of the absorption bands responsible for the vibrations of the bonds of the filler with an increase in its content in the composite, which indicates the absence of chemical and structural transformations during the creation of composites, and, therefore, confirms the optimal methods of compounding. Differential thermal analysis, regardless of FTIR spectroscopy, confirmed the formation of a carbon coating by the presence of an endothermic peak at ~ 530 ° C, which corresponds to the loss of carbon mass. Thermograms of three-phase composites are characterized by the decomposition peak of the corresponding polymers at the temperatures indicated in the literature. With the introduction of a filler and with an increase in its content in the polymer matrix, decomposition shifts to the region of higher temperatures, indicating a positive effect of the filler on the thermal stability of the studied polymers. The permittivity of composites changes slightly with frequency and practically does not decrease with increasing frequency. The electrical conductivity increases linearly with increasing frequency. The tangent of the dielectric loss angle remains constant regardless of the amount of filler in the system at a frequency of 1 kHz. A smooth increase in tanδ is observed with an increase in the volume fraction of the filler for a frequency of 1 MHz. The tanδ curve, depending on the percentage of hollandite-like ceramics, has a plateau, starting from 40 vol.% Filler for a frequency of 0.1 Hz. In contrast to two-phase composites, the dielectric properties of three-phase composites were studied at concentrations up to 30 vol%. Composites with 2.5-30 vol.% of nanoceramic filler are characterized by a lower dispersion ε 'at f <10Е02 Hz. The dispersion of the permittivity on the ε'-f curves for composites with a high content of hollandites with a carbon coating is associated with polarization processes in the ceramic ferroelectric, such as the shift of the electron density in accordance with the scheme Ti4 + + e ↔ Ti3 + and Me3 + + e ↔ Me2 +, accompanied by local motion K + ions in channels with a hollandite-like structure. It is worth noting the observed shift of the mid-frequency polarization process to a higher frequency relative to two-phase samples. Percolation thresholds for the PMMA-Kx (Ti, Me) yOz (Me = Ni, Fe, Cu) @ carbon and FT-Kx (Ti, Me) yOz (Me = Ni, Fe, Cu) @ carbon, which are in the range of 7-9 vol.%. The optimal combination of three-phase composites can be considered hollandites doped with Fe, Ni, Cu, with carbon coatings up to 2.5 wt% with a volume content of PMMA and fluoroplastic matrices up to 15 vol.%. At the same time, it should be noted that an increase in the share of carbon over 2.5% has little effect on the polarization processes of hollandite, and therefore the synergistic effect of the carbon additive decreases. The volume fraction of the filler in three-phase systems with a significant excess of the percolation threshold loses its applied interest for use in electronic components. 4 articles have been published in journals: Ceramics International (Q1), Journal of Applied Polymer Science, Russian Journal of Applied Chemistry and Russian Journal of Inorganic Chemistry.

 

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