Shape-Controlled Iron-Paraffin Composites as γ- and X-ray Shielding Materials Formable by Warmth-of-Hands-Derived Plasticity.

The design of shielding materials against ionizing radiation while simultaneously displaying enhanced multifunctional characteristics remains challenging. Here, for the first time, we present moldable paraffin-based iron nano- and microcomposites attenuating γ- and X-radiation. The moldability was gained by the warmth-of-hands-driven plasticity, which allowed for obtaining a specific shape of the composites at room temperature. The manufactured composites contained iron particles of various sizes, ranging from 22 nm to 63 µm. The target materials were widely characterized using XRD, NMR, Raman, TGA, SEM, and EDX. In the case of microcomposites, the shielding properties were developed at two concentrations: 10 and 50 wt %. The statistically significant results indicate that the iron particle size has a negligible effect on the shielding properties of the nano- and microcomposites. On the other hand, the higher iron particle contents significantly affected the attenuating ability, which emerged even as superior to the elemental aluminum in the X-ray range: at a 70 kV anode voltage, the half value layer was 6.689, 1.882, and 0.462 cm for aluminum, paraffin + 10 wt % Fe 3.5-6.5 µm, and paraffin + 50 wt % Fe 3.5-6.5 µm microcomposites, respectively. Importantly, the elaborated methodology-in situ cross-verified in the hospital studies recording real-life sampling-opens the pathway to high-performance, eco-friendly, lightweight, and recyclable shields manufactured via fully reproducible and scalable protocols.

Experimental Investigation of Thermal Conductivity of Water-Based Fe3O4 Nanofluid: An Effect of Ultrasonication Time.

Nanofluid preparation is a crucial step in view of their thermophysical properties as well as the intended application. This work investigates the influence of ultrasonication duration on the thermal conductivity of Fe3O4 nanofluid. In this work, water-based Fe3O4 nanofluids of various volume concentrations (0.01 and 0.025 vol.%) were prepared and the effect of ultrasonication time (10 to 55 min) on their thermal conductivity was investigated. Ultrasonication, up to a time duration of 40 min, was found to raise the thermal conductivity of Fe3O4 nanofluids, after which it starts to deteriorate. For a nanofluid with a concentration of 0.025 vol.%, the thermal conductivity increased to 0.782 W m-1K-1 from 0.717 W m-1K-1 as the ultrasonication time increased from 10 min to 40 min; however, it further deteriorated to 0.745 W m-1K-1 after a further 15 min increase (up to a total of 55 min) in ultrasonication duration. Thermal conductivity is a strong function of concentration of the nanofluid; however, the optimum ultrasonication time is the same for different nanofluid concentrations.

High AC and DC Electroconductivity of Scalable and Economic Graphite-Diamond Polylactide Nanocomposites.

Two types of graphite/diamond (GD) particles with different ash content was applied to prepare new electroconductive polylactide (PLA)-based nanocomposites. Four samples of nanocomposites for each type of GD particles with mass fraction 0.01, 0.05, 0.10, and 0.15 were prepared via an easily scalable method-melt blending. The samples were subjected to the studies of electrical properties via broadband dielectric spectroscopy. The results indicated up to eight orders of magnitude improvement in the electrical conductivity and electrical permittivity of the most loaded nanocomposites, in reference to the neat PLA. Additionally, the influence of ash content on the electrical conductivity of the nanocomposites revealed that technologically less-demanding fillers, i.e., of higher ash content, were the most beneficial in the light of nanofiller dispersibility and the final properties.

Thermal and Physical Characterization of PEG Phase Change Materials Enhanced by Carbon-Based Nanoparticles.

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g·mol-1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3-3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64-0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du Noüy ring tensiometer and a drop-shape analyzer.

Carbon Nanomaterial-Based Nanofluids for Direct Thermal Solar Absorption.

Recently, many scientists have been making remarkable efforts to enhance the efficiency of direct solar thermal absorption collectors that depends on working fluids. There are a number of heat transfer fluids being investigated and developed. Among these fluids, carbon nanomaterial-based nanofluids have become the candidates with the most potential by the heat absorbing and transfer properties of the carbon nanomaterials. This paper provides an overview of the current achievements in preparing and exploiting carbon nanomaterial-based nanofluids to direct thermal solar absorption. In addition, a brief discussion of challenges and recommendations for future work is presented.

Electrical and Optical Properties of Silicon OxideLignin Polylactide (SiO2-L-PLA).

This paper presents a study on the electrical properties of new polylactide-basednanocomposites with the addition of silicon-dioxide-lignin nanoparticles and glycerine as a plasticizer.Four samples were prepared with nanoparticle mass fractions ranging between 0.01 to 0.15(0.01, 0.05, 0.10, and 0.15), and three samples were prepared without nanoparticle filler-unfilledand unprocessed polylactide, unfilled and processed polylactide, and polylactide with Fusabondand glycerine. All samples were manufactured using the melt mixing extrusion techniqueand injection molding. Only the unfilled and unprocessed PLA sample was directly preparedby injection molding. Dielectric properties were studied with broadband spectroscopy in a frequencyrange from 0.1 Hz to 1 MHz in 55 steps designed on a logarithmic scale and a temperature rangefrom 293.15 to 333.15 K with a 5 K step. Optical properties of nanocomposites were measuredwith UV-VIS spectroscopy at wavelengths from 190 to 1100 nm. The experimental data show thatthe addition of silicon-dioxide-lignin and glycerine significantly affected the electrical propertiesof the studied nanocomposites based on polylactide. Permittivity and electrical conductivity showa significant increase with an increasing concentration of nanoparticle filler. The optical properties arealso affected by nanofiller and cause an increase in absorbance as the number of silicon-dioxide-ligninnanoparticles increase.

Effect of sonication characteristics on stability, thermophysical properties, and heat transfer of nanofluids: A comprehensive review.

The most crucial step towards conducting experimental studies on thermophysical properties and heat transfer of nanofluids is, undoubtedly, the preparation step. It is known that good dispersion of nanoparticles into the base fluids leads to having long-time stable nanofluids, which result in having higher thermal conductivity enhancement and lower viscosity increase. Ultrasonic treatment is one of the most effective techniques to break down the large clusters of nanoparticles into the smaller clusters or even individual nanoparticles. The present review aims to summarize the recently published literature on the effects of various ultrasonication parameters on stability and thermal properties of various nanofluids. The most common methods to characterize the dispersion quality and stability of the nanofluids have been presented and discussed. It is found that increasing the ultrasonication time and power results in having more dispersed and stable nanofluids. Moreover, increasing the ultrasonication time and power leads to having higher thermal conductivity and heat transfer enhancement, lower viscosity increase, and lower pressure drop. However, there are some exceptional cases in which increasing the ultrasonication time and power deteriorated the stability and thermophysical properties of some nanofluids. It is also found that employing the ultrasonic horn/probe devices are much more effective than ultrasonic bath devices; lower ultrasonication time and power leads to better results.

Electrical Conductivity and Dielectric Properties of Ethylene Glycol-Based Nanofluids Containing Silicon Oxide-Lignin Hybrid Particles.

This paper presents results of experimental investigation into dielectric properties of silicon oxide lignin (SiO2-L) particles dispersed with various mass fractions in ethylene glycol (EG). Measurements were conducted at a controlled temperature, which was changed from 298.15 to 333.15 K with an accuracy of 0.5 and 0.2 K for dielectric properties and direct current (DC) electrical conductivity, respectively. Dielectric properties were measured with a broadband dielectric spectroscopy device in a frequency range from 0.1 to 1 MHz, while DC conductivity was investigated using a conductivity meter MultiLine 3410 working with LR925/01 conductivity probe. Obtained results indicate that addition of even a small amount of SiO2-L nanoparticles to ethylene glycol cause a significant increase in permittivity and alternating current (AC) conductivity as well as DC conductivity, while relaxation time decrease. Additionally, both measurement methods of electrical conductivity are in good agreement.

Influence of Six Carbon-Based Nanomaterials on the Rheological Properties of Nanofluids.

Nanofluids, dispersions of nanosized solid particles in liquids, have been conceived as thermally-improved heat transfer fluids from their conception. More recently, they have also been considered as alternative working fluids to improve the performance of direct absorption solar thermal collectors, even at low nanoadditive concentrations. Carbon-based nanomaterials have been breaking ground in both applications as nanoadditives during the last decade due to their high thermal conductivities and the huge transformation of optical properties that their addition involves. In any application field, rheological behavior became a central concern because of its implications in the pumping power consumption. In this work, the rheological behavior of four different loaded dispersions (0.25, 0.50, 1.0, and 2.0 wt%) of six carbon-based nanomaterials (carbon black, two different phase content nanodiamonds, two different purity graphite/diamond mixtures, and sulfonic acid-functionalized graphene nanoplatelets) in ethylene glycol:water mixture 50:50 vol% have been analysed. For this purpose, a rotational rheometer with double cone geometry was employed, which included a special cover to avoid mass losses due to evaporation at elevated temperatures. The flow curves of the twenty-four nanofluids and the base fluid were obtained by varying the shear rate between 1 and 1000 s-1 for seven different temperatures in the range from 283.15 to 353.15 K. The shear-thinning behaviors identified, as well as their dependences on carbon-based nanomaterial, concentration, and temperature, were analyzed. In addition, oscillatory tests were performed for samples with the clearest Non-Newtonian response, varying the deformation from 0.1 to 1000% with constant frequency and temperature. The dependence of the behaviors identified on the employed carbon-based nanomaterial was described.

Synthesis and electrochemical characterization of electroactive IoNanofluids with high dielectric constants from hydrated ferrous sulphate.

An iron oxide based-electroactive IoNanofluid with a high dielectric constant, high stability and low viscosity was synthesized from ferrous sulphate heptahydrate via a facile microwave assisted one-step route in 1-butyl-4-methylpyridinium chloride. The IoNanofluid exhibited CE coupled faradaic redox reactions involving reversible chemical reaction and reversible electron transfer steps. A transition from diffusion controlled to surface controlled capacitive processes was observed at varying scan rates. The efficiency of the charge-discharge process was greater than 94% even after 100 cycles.

Theoretical Probing of Weak Anion-Cation Interactions in Certain Pyridinium-Based Ionic Liquid Ion Pairs and the Application of Molecular Electrostatic Potential in Their Ionic Crystal Density Determination: A Comparative Study Using Density Functional Approach.

A comprehensive study on the structure, nature of interaction, and properties of six ionic pairs of 1-butylpyridinium and 1-butyl-4-methylpyridinium cations in combination with tetrafluoroborate (BF4-), chloride (Cl-), and bromide (Br-) anions have been carried out using density functional theory (DFT). The anion-cation interaction energy (ΔEint), thermochemistry values, theoretical band gap, molecular orbital energy order, DFT-based chemical activity descriptors [chemical potential (µ), chemical hardness (η), and electrophilicity index (ω)], and distribution of density of states (DOS) of these ion pairs were investigated. The ascendancy of the -CH3 substituent at the fourth position of the 1-butylpyridinium cation ring on the values of ΔEint, theoretical band gap and chemical activity descriptors was evaluated. The ΔEint values were negative for all six ion pairs and were highest for Cl- containing ion pairs. The theoretical band gap value after -CH3 substitution increased from 3.78 to 3.96 eV (for Cl-) and from 2.74 to 2.88 eV (for Br-) and decreased from 4.9 to 4.89 eV (for BF4-). Ion pairs of BF4- were more susceptible to charge transfer processes as inferred from their significantly high η values and comparatively small difference in ω value after -CH3 substitution. The change in η and µ values due to the -CH3 substituent is negligibly small in all cases except for the ion pairs of Cl-. Critical-point (CP) analyses were carried out to investigate the AIM topological parameters at the interionic bond critical points (BCPs). The RDG isosurface analysis indicated that the anion-cation interaction was dominated by strong Hcat···Xani and Ccat···Xani interactions in ion pairs of Cl- and Br- whereas a weak van der Waal's effect dominated in ion pairs of BF4-. The molecular electrostatic potential (MESP)-based parameter ΔΔVmin measuring the anion-cation interaction strength showed a good linear correlation with ΔEint for all 1-butylpyridinium ion pairs (R2 = 0.9918). The ionic crystal density values calculated by using DFT-based MESP showed only slight variations from experimentally reported values.

Experimental Investigation of Electrical Conductivity and Permittivity of SC-TiO 2 -EG Nanofluids.

The paper presents experimental studies of dielectric properties of nanofluids based on ethylene glycol and SC-TiO2 nanoparticles with average size of 15-40 nm with various mass concentrations. The dielectric permittivity both real part and imaginary part as a function of temperature and frequency were measured. Also, dependence ac conductivity on frequency, temperature, and mass concentration were investigated. Based on the curves of ac conductivity, dc conductivity was calculated, and 400 % enhancement in dc conductivity was exposed.

Influence of anisotropic pressure on viscosity and electrorheology of diethylene glycol-based MgAl2O4 nanofluids.

The paper presents results of rheological experiments on viscosity under anisotropic pressure and in electric field of diethylene glycol-based MgAl2O4 nanofluids. Nanofluids have been prepared in a two-step method. The dynamic viscosity of nanofluids with various mass concentrations of nanoparticles was measured in the range of shear rates from 10 s -1 to 1,000 s -1 in constant temperature under the pressure of 7.5 MPa. In the second type of experiments, different values of the electric field up to 2,000 V/mm was used. Thixotropy structure of MgAl2O4-DG nanofluids has been studied in electrical field.

Dependence of viscosity of suspensions of ceramic nanopowders in ethyl alcohol on concentration and temperature.

: This work presents results of measurements of viscosity of suspensions including yttrium oxide (Y2O3), yttrium aluminum garnet (Y3Al5O12) and magnesium aluminum spinel (MgAl2O4) nanopowders in ethanol. Nanoparticles used in our research were either commercially available (Baikowski) or nanopowders newly developed in the Institute of Ceramics and Building Materials in Warsaw, Poland. The study was conducted in a wide range of shear rates (0.01 to 2,000 s-1) and temperature interval from -15°C to 20°C. A Haake Mars 2 rheometer from Thermo Fisher, Germany, was used in the Biophysics Laboratory at Rzeszów University of Technology. Most of the samples show a non-Newtonian behaviour. It was confirmed with a Rheo-NMR system from Bruker that 10% by weight of Y2O3 suspension is a non-Newtonian fluid. In this work, we also report an unexpected behaviour of the viscosity of some samples (Y2O3 and Y3Al5O12) due to sedimentation effect.

Viscosity of suspensions of yttrium oxide (Y2O3) nanopowder in ethyl alcohol.

This paper presents results from measurements of viscosity of suspensions of Yttrium Oxide Y2O3 ceramic nanopowder in ethyl alcohol. The study was conducted at the request of and in cooperation with the ICMB. This research will add important information about the formation and viscosity characteristics of suspensions of nanopowders. The behavior of nanopowder suspensions has been examined in a wide range of shear rates from 0.01 s(-1) to 2000 s(-1). Additionally, the behavior of the suspension has been studied in the temperature range from -15 degrees C to 20 degrees C. Complementary experiments have been performed by application of a Rheo-NMR at Bruker Biospin and by the use of RheoScope at ThermoFisher companies.