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Highly thermostable low-k polymer films with potential applications as dielectric materials in microelectronic industry were synthesized starting from 9,9-bis [4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride and various diamines. A polyetherimide/silica nanocomposite film was obtained using methyltriethoxysilane as precursor of inorganic phase. The chemical structure was confirmed by FTIR and [sup.1] NMR spectroscopy. Water vapor's sorption capacity, thermal stability, glass transition temperature, thermal diffusivity, specific heat, thermal conductivity, and dielectric characteristics of the films were determined. All the films exhibited excellent thermal stability, with an initial decomposition temperature in the range of 500-530[degrees]C. They showed low dielectric constant of 1.98-2.86 and low dielectric loss of 0.0037-0.011, at a frequency of 1 Hz and room temperature. The subglass [gamma]- and [beta]-relaxations, primary [alpha]-relaxation, and conductivity relaxation processes were discussed according to the chemical structure of the samples. Quantitative structure-property relationship (QSPR) study was conducted, and linear regression models were formulated to describe the causal relationships between different parameters and polyetherimide properties. KEYWORDS dielectric properties, fluorene groups, polyetherimides, QSPR study, thermal characteristics, 1 | INTRODUCTION Low dielectric constant (low-k) aromatic polyimides represent an important class of thermostable heterocyclic polymers that can be used in electronic industry as dielectrics between layers in thin [...]

This paper aims to study the possibility of improving the chemical and surface characteristics of the Ti6Al4V alloy by depositing phosphate layers on its surface. Accordingly, an innovative phosphating solution was developed and used in a chemical conversion process to obtain Ca–Zn phosphate layers on the base material surface. Moreover, the chemical composition of the phosphate solution was chosen considering the biocompatibility of the chemical elements and their possibility of contributing to the formation of phosphate compounds. The obtained layer was characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and potentiodynamic polarization tests. The wetting of the Ca–Zn sample surface was also investigated using water and two liquids similar to body fluids, namely, Ringer and Dulbecco solutions. According to the surface energy study, the polar component is almost two times larger compared with the dispersive one. The SEM and EDS tests revealed a uniformly coated surface with intercalated crystals leading to a rough surface. Furthermore, the XRD results showed not only the presence of hopeite and scholzite but also of phosphophyllite. By the vibrations of the PO4−3 groups, the FTIR test confirmed the presence of these phases. The potentiodynamic tests revealed that the samples coated with the Ca–Zn phosphate layer present better corrosion resistance and a lower corrosion rate compared with the uncoated ones. [ABSTRACT FROM AUTHOR]

Determining the phase transition temperature of different types of liquid crystals based on their structural parameters is a complex problem. The experimental work might be eliminated or reduced if prediction strategies could effectively anticipate the behavior of liquid crystalline systems. Neuro-evolutive modeling based on artificial neural networks (ANN) and a differential evolution (DE) algorithm was applied to predict the phase transition temperatures of bent-core molecules based on their resorcinol core. By these means, structural parameters such as the nature of the linking groups, the position, size and number of lateral substituents on the central core or calamitic wings and the length of the terminal chains were taken into account as factors that influence the liquid crystalline properties. A number of 172 bent-core compounds with symmetrical calamitic wings were selected from the literature. All corresponding structures were fully optimized using the DFT, and the molecular descriptors were calculated afterward. In the first step, the ANN-DE approach predicted the mesophase presence for the analyzed compounds. Next, ANN models were determined to predict the transition temperatures and whether or not the bent-core compounds were mesogenic. Simple structural, thermophysical and electronic structure descriptors were considered as inputs in the dataset. As a result, the models determined for each individual temperature have an R2 that varied from 0.89 to 0.98, indicating their capability to estimate the transition temperatures for the selected compounds. Moreover, the impact analysis of the inputs on the predicted temperatures showed that, in most cases, the presence or not of liquid crystalline properties represents the most influential feature. [ABSTRACT FROM AUTHOR]

Novel systems based on modified azo-polysiloxanes and gelatin with potential biological applications were prepared and characterized. Simultaneous rheological and UV irradiation studies allowed evidencing structural modification inside the gelatin matrix. For all analyzed samples a shift in the temperature corresponding to the physical network destructuration, from 30°C (corresponding to gelatin) to 40°C (for the composite) was noticed. The experimental results proved the existence of interactions between gelatin and polysiloxanes intensified after UV irradiation. The increase in the values of G' and G" is a consequence of system restructuration leading to more arranged architectures able to release the included active principle. As a function of the azopolysiloxane structure, the destructuration temperature of the composite can be tuned in the domain 30-40°C. [ABSTRACT FROM AUTHOR]