Investigating optimal region for thermal and electrical properties of epoxy nanocomposites under high frequencies and temperatures

This research investigates the optimal region to achieve balanced thermal and electrical insulation properties of epoxy (EP) under high frequency (HF) and high temperature (HT) via integration of surface-modified hexagonal boron nitride (h-BN) nanoparticles. The effects of nanoparticle content and high temperature on various electrical (DC, AC, and high frequency) and thermal properties of EP are investigated. It is found that the nano h-BN addition enhances thermal performance and weakens electrical insulation properties. On the other side, under HF and HT stress, the presence of h-BN nanoparticles significantly improves the electrical performance of BN/EP nanocomposites. The EP has superior insulation properties at low temperature and low frequency, whereas the BN/EP nanocomposites exhibit better insulation performance than EP under HF and HT. The factors such as homogeneous nanoparticle dispersion in EP, enhanced thermal conductivity, nanoparticle surface modification, weight percent of nanoparticles, the mismatch between the relative permittivity of EP and nano h-BN, and the presence of voids in nanocomposites play the crucial role. The optimal nanoparticle content and homogenous dispersion can produce suitable EP composites for the high frequency and high temperature environment, particularly solid-state transformer applications.

The Effect of Aluminum Oxide Nanoparticles on the Activity of Amylases of the Enzyme Preparation of Microbial Origin

На основании анализа литературных данных показано, что изучение влияния наночастиц, в том числе оксида алюминия, на активность целевых ферментов микробных ферментных препаратов, применяемых в пивоваренном производстве, целесообразно. Приведены данные о влиянии наночастиц Al2O3 на процесс гидролиза крахмала в модельных средах под действием амилаз ферментного препарата «АПСубтилин П». Показано, что присутствие наночастиц в реакционной среде приводит к снижению амилолитической активности и, как следствие, снижению концентрации редуцирующих веществ в гидролизате на 12-15% (при содержании наночастиц 0,1 мг/см3) и на 34% (при содержании наночастиц 1,0 мг/см3) по сравнению с контролем. Установлено, что увеличение продолжительности ферментативного гидролиза с 60 до 120 мин приводит к ослаблению ингибирующего воздействия наночастиц Al2O3 на амилолитическую активность ферментного препарата. При этом присутствие наноразмерных объектов указанного типа не оказало негативного воздействия на результаты лабораторного затирания, проводимого по настойному способу с тремя паузами: основные показатели первого сусла опытных вариантов не уступали аналогичным характеристикам контрольного образца. На основании приведенных данных сделано заключение о нежелательности присутствия наночастиц Al2O3 в реакционных средах амилаз микробного происхождения в концентрациях, превышающих 0,1 мг/см3. The expediency of studying the effect of nanoparticles, in particular, aluminum oxide, on the activity of target enzymes of enzyme preparations used in brewing is substantiated based on the analysis of the literature data. Data on the effect of Al2O3 nanoparticles on the process of starch hydrolysis in model media under the action of amylases of the enzyme preparation «APSubtilin P» are presented. It has been shown that the presence of nanoparticles in the reaction medium leads to a decrease in amylolytic activity and, as a consequence, a decrease in the concentration of reducing substances in the hydrolyzate by 12-15% (at nanoparticle content of 0.1 mg/cm3) and by 34% (at nanoparticle content of 1, 0 mg/cm3) compared to the control. It was found that the increase in the duration of enzymatic hydrolysis from 60 to 120 min leads to a weakening of the inhibitory effect of Al2O3 nanoparticles on the amylolytic activity of the enzyme preparation. At the same time, the presence of nanoscale objects of this type did not have a negative impact on the results of laboratory mashing, carried out according to the infusion method with three pauses: the main indicators of the first wort of the experimental variants were not inferior to those of the control sample. Based on the data presented, it was concluded that the presence of Al2O3 nanoparticles in the reaction media of amylases of microbial origin in concentrations exceeding 0.1 mg/cm3 is undesirable.

Effect of Fumed Silica Nanoparticles on Ultraviolet Aging Resistance of Bitumen

In this study, bitumen modified by fumed silica nanoparticles was characterized through dynamic shear rheometer tests, scanning electron microscopy, and Fourier transform infrared spectroscopy. The fumed silica nanoparticles were used in three different ratios, i.e., 0.1, 0.2 and 0.3 wt.-% of bitumen. Specifically, the modified bitumen characteristics were studied after laboratory aging by analyzing the chemical composition and rheological properties. From the determination of oxidation degree and carbonyl index it was found that the resistance of the modified bitumen to ultraviolet aging was improved with the increasing nanoparticle content. In bitumen modified by fumed silica nanoparticles, the nanoparticles were well dispersed. Moreover, the results illustrated that the bitumen properties were improved, and the improvement effect of 0.1 wt.-% fumed silica nanoparticles was more distinct than the higher concentrations.

Modulus, Strength and Cytotoxicity of PMMA-Silica Nanocomposites

Key advantages of Poly(methyl methacrylate)—PMMA for denture application are related to aesthetics and biocompatibility, while its main deficiency is related to mechanical properties. To address this issue, SiO2 nanoparticle reinforcement was proposed, containing 0 to 5% nanosilica, to form nanocomposite materials. Flexural strengths and elastic moduli were determined and correlated to nominal nanoparticle content and zeta potential of the liquid phase nanoparticle solutions. Another issue is the biocompatibility, which was determined in terms of cytotoxicity, using L929 and MRC5 cell lines. The addition of nanoparticle was proved to be beneficial for increasing flexural strength and modulus, causing a significant increase in both strength and moduli. On the other hand, the formation of agglomerates was noted, particularly at higher nanoparticle loadings, affecting mechanical properties. The addition of nanosilica had an adverse effect on the cytotoxicity, increasing it above the level present in unmodified specimens. Cytotoxic potential was on the acceptable level for specimens with up to 2% nanosilica. Consequently, nanosilica proved to be an effective and biocompatible means of increasing the resistance of dental materials.

The influence of titanium dioxide (TiO2) nanoparticles on the structure, optical and dielectric properties of polyvinyl chloride (PVC)

The tendency to improve the properties of insulating materials by incorporating inorganic nanoparticles has become necessary in order to design new insulation systems. In this study, PVC/TiO2-based nanocomposites with different loadings (3, 5 and 10 wt.%) of TiO2 nanoparticles were prepared by the solution mixing method. The morphology of the prepared nanocomposites was studied by Atomic Force Microscope (AFM). Experimentally, it was found that as the concentration increases, the size of the surface structural elements and particle size increases. Photoluminescence (PL) analysis of samples shows improvement compared to the pristine polymer. Furthermore, PL intensity for nanocomposites increases depending on the concentration and saturation occurs at a certain amount of titanium dioxide nanoparticles. The increase in luminescence intensity till a certain nanoparticle content is due to the growth of the luminescent surface area. Further saturation is explained by the increase in particle size with no increase or a slight reduction in surface area. Dielectric properties of nanocomposites were studied. It was found that dielectric permittivity of the materials increases as the nanoparticle volume content increases and it reaches at its highest value for the nanocomposites with 3% nanoparticle content. The optical properties of the polymer and nanocomposite films were studied in the region 200 nm to 600 nm. It was found that the PVC/TiO2 nanocomposites showed enhancement in the absorbance intensities which was more significant for the nanocomposites with higher nanoparticle content compared to the pristine polymer. Furthermore, absorption spectra were used to calculate the optical bandgap of the prepared nanocomposite films and redshift observed in the calculated values of bandgap for nanocomposites. Consequently, it was proved that by incorporating TiO2 nanoparticles into the polymer matrix, the spectral region of the samples can be expanded resulting in broadened application of such systems in various fields of science and technology.