Analytical formulas for complex permittivity of periodic composites. Estimation of gain and loss enhancement in active and passive composites

ABSTRACT

The asymptotic homogenization method is applied to complex dielectric periodic composites. An equivalence to coupled dielectric problems with real coefficients is shown. This is similar to a piezoelectric problem: an out-plane mechanical displacement and an in-plane electric potential establishing a correspondence principle. Closed-form formulas for the complex dielectric effective tensor in the case of a square array of circular inclusions embedded in a matrix are given. These formulas are written in terms of a real and symmetric matrix which facilitates the implementation of the computational scheme. We also get similar formulas for multilayered complex dielectric composites. The real closed-form formulas are advantageous for estimating gain and loss enhancement properties of active and passive composites in certain volume fraction intervals. Numerical computations are performed and the results are compared with other approaches showing the usefulness of the obtained formulas. This may be of interest in the context of metamaterials.     

Determination of tensile strength of UHMWPE fiber-reinforced polymer composites

Quasi-static tensile test of UHMWPE fiber-reinforced composite laminate is challenging to perform due to low interlaminar shear strength and low coefficient of friction. Tensile tests proposed in the literature were conducted and limitations associated with each method led to the evolution of a new method. Tensile test of single-ply was realized as the best representative of tensile strength of a composite than tensile test of UHMWPE laminate. A fixture was developed for single-ply tests which increased friction and provided the mechanical constraint to slipping. The fixture is easy to fabricate and has provided repeatable results for eight grades of UHMWPE fiber-based (0/90) fabrics. Reported tensile strengths are in quite high range of 900–1500 MPa.     

Atomic force microscopy study of polypropylene-based self-reinforced composites

Self-reinforced composites are polymeric materials formed by a reinforcement core and a low-melting point skin, which acts as a matrix after the consolidation step. These materials are widely exploited in industrial applications for their mechanical resistance and durability, which are themselves influenced by processing conditions and polymer composition. In the present work, two similar polypropylene-based commercial fabrics were used to evaluate the surface modifications after laminate compaction and after artificial aging using atomic force microscopy. The results were correlated with the chemical and physical-chemical interactions obtained from scanning electron microscopy, transmission electron microscopy, raman and thermal analysis experiments. Single tape consolidated laminate before and after aging displayed different superficial features that can explain the differences in the macroscopic behavior of the two products.     

High strength,acid-resistant composites from canola,sunflower, or linseed oils: Influence of triglyceride unsaturation on material properties

Here are reported composites made by crosslinking unsaturated units in canola, sunflower, or linseed oil with sulfur to yield CanS , SunS , and LinS , respectively. These plant oils were selected because the average number of crosslinkable unsaturated units per triglyceride vary from 1.3 for canola to 1.5 for sunflower and 1.8 for linseed oil. The remeltable composites show compressive strengths that increase with increasing unsaturation number from CanS (9.3 MPa) to SunS (17.9 MPa) to LinS (22.9 MPa). These values for SunS and LinS are competitive when compared with the value of 17 MPa required for residential building using traditional Portland cement. The plant oil composites are recyclable over many cycles and can retain up to 100% of strength after 24 hr in oxidizing acid under conditions where Portland cement is dissolved in under 30 min. Infusion of the composites into premade cement blocks affords them with significantly improved acid resistance as well. This work thus provides a simple, nearly 100% atom economical route to convert plant oils and waste sulfur to composites having enhanced performance over commercial structural materials.     

On the Integration of Dielectrometry into Electrochemical Impedance Spectroscopy to Obtain Characteristic Properties of a Dielectric Thin Film

We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in-situ growth-monitoring of a nanoporous, crystalline thin film (HKUST-1) on an interdigitated electrode geometry.     

High performance carbon–carbon composites obtained by a two-step process from phthalonitrile matrix composites

Carbon–carbon composites (C/C) were produced from carbon fiber reinforced phthalonitrile (CFRP) matrix composites in a two-step impregnation–carbonization procedure. After graphitization at 1800 °C, the obtained C/C composites demonstrated highly crystalline structure and properties characteristic of composites derived from phenolic matrix CFRP by the industrial procedure: d = 1.73 g cm^?3, interlaminar shear strength was 14.1 MPa, compression strength was 139.8 MPa, and coefficient of friction was in the range 0.32–0.34.     

Efficient Piezoelectric Energy Harvesting from a Discrete Hybrid Bismuth Bromide Ferroelectric Templated by Phosphonium Cation

Bismuth containing hybrid molecular ferroelectrics are receiving tremendous attention in recent years owing to their stable and non-toxic composition. However, these perovskite-like structures are primarily limited to ammonium cations. Herein, we report a new phosphonium based discrete perovskite-like hybrid ferroelectric with a formula [Me(Ph)₃P]₃[Bi₂Br₉] ( MTPBB ) and its mechanical energy harvesting capability. The Polarization-Electric field (P-E) measurements resulted in a well-defined ferroelectric hysteresis loop with a remnant polarization value of 2.1 μC cm⁻². Piezoresponse force microscopy experiments enabled visualization of the ferroelectric domain structure and evaluation of the piezoelectric strain coefficient (d₃₃) for an MTPBB single crystal and thin film sample. Furthermore, flexible devices incorporating MTPBB in polydimethylsiloxane (PDMS) matrix at various concentrations were fabricated and explored for their mechanical energy harvesting properties. The champion device with 20 wt % of MTPBB in PDMS rendered a maximum peak-to-peak open-circuit voltage of 22.9 V and a maximum power density of 7 μW cm⁻² at an optimal load of 4 MΩ. Moreover, the potential of MTPBB -based devices in low power electronics was demonstrated by storing the harvested energy in various electrolytic capacitors.     

Highly Sensitive Enzyme-free Sensor Based on a Carbon Paste Electrode Modified with Binary Zinc Oxide/Polyaniline Nanocomposites for Dopamine,Ascorbic Acid and Uric Acid Sensing

Hybrid composites ZnO/PANI were facily synthesized by a sonication process at room temperature. This procedure is non-expensive, time/energy saving and environmentally safe. The as-prepared ZnO/PANI were characterized by FTIR, UV-vis spectroscopies and SEM in order to investigate the structure and morphology of the studied composites. The samples were used to modify carbon paste electrode (CPE) in order to develop electrochemical biosensors (ZnO/PANI/CPE). The sensing properties of the nanoparticles were evaluated for dopamine, ascorbic acid and uric acid non-enzymatic detection. The effect of percentage of polyaniline in the composites and the effect of calcination on the biosensor's response were also examined in the present study. It was revealed that the existence of PANI in ZnO/PANI/CPE largely enhanced the electroactive surface area and therefore the sensitivity for electrochemical sensing. A good electrochemical behavior was noted for ZnO/40 wt% PANI-cal/CPE modified electrode toward DA, AA and UA oxidation. The electroactive surface area of the previously mentioned modified electrode (0.235 cm²) was two times higher than that of the bare electrode (0.117 cm²). The liner relationships between current intensities and concentrations were found to be 0.01–1.4 mM, 0.1–1.3 mM and 0.01–0.12 mM, with detection limit of 0.029 mM, 0.063 mM and 0.007 mM, for DA, AA and UA respectively. In the mixtures of ascorbic acid (AA), dopamine (DA) uric acid (UA) and glucose (Glu) the sensor showed high selectivity of DA with low interference of ascorbic acid by a current change of 14 %. The as-prepared ZnO/PANI/CPE biosensor displayed a good reproducibility and stability.     

Effect of weighting materials on carbonation of oil well cement-based composites under high temperature and CO2-rich environment

As an indispensable part of cement slurry for high temperature and high pressure oil and gas wells, weighting materials have a significant impact on the carbon dioxide corrosion of oil well cement-based composites.This paper studied the carbonation process of cement with three weighting agents, and evaluated the compressive strength and carbonation depth of cement at 150 ℃. XRD, SEM and MIP were used to study the carbonation mechanism of cement. When 21 days of carbonation, the carbonation depth growth rate of hausmannite cement was 0.21 mm/d, hematite cement was 0.24 mm/d, and barite cement was 0.31 mm/d. The compressive strength of cement decreased after carbonation,and the carbonation had a minor influence on the compressive strength of hausmannite cement and the most significant impact on barite cement. The carbonation product of oil well cement was mainly calcite. Unstable vaterite mainly existed in the barite cement sample, indicating that the barite cement sample was the most serious corrosion. In the carbonation zone, the number of pores smaller than 10 nm increased the most in the hausmannite cement sample. Pores with a diameter greater than 100 nm accounted for 1.9 % in the hausmannite cement, 3.0 % in hematite cement, and 4.8 % in barite cement. The result shows that hausmannite is the most conducive to the corrosion resistance of oil well cement.     

3D Printable Geopolymer Composites Reinforced with Carbon-Based Nanomaterials – A Review

Three-dimensional (3D) geopolymer printing (3DGP) technology is a rapidly evolving digital fabrication method used in the construction industry. This technology offers significant benefits over 3D concrete printing in terms of energy saving and reduced carbon emissions, thus promoting sustainability. 3DGP technology is still evolving, and researchers are striving to develop high-performance printable materials and different methods to improve its robustness and efficiency. Carbon-based nanomaterials (CBNs) with beneficial properties have a wide range of applications in various fields, including as concrete/geopolymer systems in construction. This paper comprehensively reviews the research progress on carbon-based nanomaterials (CBNs) used to develop extrusion-based 3D geopolymer printing (3DGP) technology, including dispersion techniques, mixing methods, and the materials′ performance. The rheological, mechanical, durability, and other characteristics of these materials are also examined. Furthermore, the existing research limitations and the prospects of using 3DGP technology to produce high-quality composite mixtures are critically evaluated.