Predicting interactive behavior of cytokines and their receptors by dielectric thermal analysis and thermogravimetry

Cytokines and soluble cytokine receptors serve as important protein biomarkers for chronic and infectious disease diagnosis. The development of biosensors capable of detecting cytokines or their soluble receptors in patient bodily fluids is a growing area of research. In an ongoing series of studies to understand the thermal analytical behavior of cytokines and their soluble receptors, dielectric thermal analysis (DETA) and thermogravimetry (TG) were used in investigations to determine if differentiations based on dielectric properties (e.g., conductivity) of the proteins could be identified. Permittivity (ε′) and dielectric loss factor (ε″) measurements were performed over a frequency range of 0.1–300,000 Hz. Up to 20 min, water associated with the samples was conductive, interacting with the proteins and affecting the temperature-dependent relaxation spectra of proteins. A trend analysis revealed differences between surface charge at 0.1 Hz and bulk charge at 300,000 Hz. In addition, the greatest change detected among proteins was due to the conductivity (dielectric loss factor). Beyond a 20 min drying time, the observed conductivity was due to intrinsic properties of the proteins with limited dependence on frequency. A 100% water loss was obtained for samples within 20–30 min by TG. Sample drying by TG could serve as a preparatory step in drying protein samples for further DETA and DSC analysis.     

Microstructural,physical, and thermal analyses of Portland cement–fly ash–calcium hydroxide blended pastes

The effect of calcium hydroxide (CH) on the properties of Portland–fly ash cement pastes, at up to high-volume fly ash mixes has been investigated using normal consistency, setting time, compressive strength, thermal analysis and scanning electron microscope. CH as an additive material (5 and 10 wt%), lignite fly ash (FA) up to 50 wt% was used to produce Portland cement (PC)–FA–CH pastes at w/PC + FA ratio of 0.5. Water requirement for normal consistency was found to increase with increasing CH content while a decrease in initial setting time was found. Furthermore, the compressive strengths of all FA mixes with CH were found to be higher than the mixes without CH. Thermal analysis and scanning electron microscope were used to study the hydration of PC–FA–CH system. The results showed that the first phase transition detected by thermal analyses was attributed to ettringite, calcium silicate hydrate, gehlenite hydrate and was found to be higher in PC–FA–CH mixes than in pure Portland–FA cement paste resulting in an increase in compressive strength. Moreover, the hydration phases were also found to increase with increasing curing time. Overall, the results show that the additional of 5 wt% CH in Portland–FA mixes especially at high-volume FA mixes was found to accelerate FA pozzolanic reaction at early ages (7 and 28 days), resulting to an increase in compressive strength.     

Thermal behaviour and characterization of cement composites with burnt kaolin sand

The kaolin sand containing 36 wt% of kaolinite was thermally transformed at 650 °C/L h to the burnt kaolin sand (BKS) with relevant content of metakaolinite. Thermal behaviour of composites with substitution of Portland cement (PC) by the BKS containing 0, 5, 10 and 15 wt% of metakaolinite and water-to-solid ratio of 0.5 kept for 90 days in 20 ± 1 °C water was studied by thermal analysis. TG/DTA/DTG studies concerned calciumsilicate hydrate and calciumaluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The reduction in portlandite content was observed in PC–BKS composites opposite to that found in the reference PC system. Compressive strength uptakes were observed in PC–BKS composites relative to that of reference PC system. BKS is characterized as effective pozzolanic material giving cement composites of high performance. The above findings were confirmed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) results.     

PMMA-SiO<Subscript>2</Subscript> organic–inorganic hybrid films: determination of dielectric characteristics

Organic–inorganic hybrid thin films have been prepared by a modified sol–gel route using tetraethyl orthosilicate as the inorganic (silica) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxysilylpropyl methacrylate as the coupling agent. The films were prepared by spin coating on Si (100) p-type substrates and subsequently heat-treated at 90 °C. Fourier transform infrared results reveal a set of absorption bands associated with the formation of both PMMA and SiO₂ phases in the hybrid films. Capacitance–voltage (C–V) characterization was carried out on metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures, with the hybrid films as the insulator layer to evaluate the electrical properties. We present a detailed comparative analysis of the dielectric constant obtained from C–V characterization in the frequency range of 1 kHz–1 MHz. For the PMMA-SiO₂ hybrid material the dielectric constant values obtained were around 9.5 at 1 MHz which is superior to the values reported for thermally grown SiO₂ and pure PMMA materials. The interface state density for PMMA-SiO₂ on Si was approximately 10¹⁰ cm⁻², which is comparable to the standard SiO₂/Si structures. Due to the electrical behavior and low processing temperatures this hybrid dielectric is a very promising candidate for flexible electronic devices and its subsequent implementation does not require complex equipment.     

Dielectric,ferroelectric and optical properties of BaZr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>O<Subscript>3</Subscript> thin films prepared by sol–gel-hydrothermal process

BaZr_0.2Ti_0.8O₃ thin films on Pt/Ti/SiO₂/Si substrates have been fabricated under low temperature conditions by a sol–gel-hydrothermal technique. The dielectric constant is 247–83 in the frequency range of 1 kHz–1 MHz. The corresponding dielectric loss is ~10⁻². The capacitance–voltage curve shows strong non-linear dielectric behavior leading to a high tunability, up to ~30% at 1 kHz. The remanent polarization and coercive field at room temperature are measured to be ~1.5 μC/cm² and ~90 kV/cm. The infrared optical properties of the thin films are investigated using an infrared spectroscopic ellipsometry in the wave number range of 800–4,000 cm⁻¹. Optical constants of the thin films are simultaneously obtained.     

Thermally-induced dielectric relaxation spectra in three aldohexose monosaccharides

Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts. Phase transitions, including glass transition (T _g) and melting temperature (T _m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and solid–liquid transitions.     

Thermally stimulated current and differential scanning calorimetry spectroscopy for the study of polymer nanocomposites

The thermally stimulated discharge current (TSC) and differential scanning calorimetry (DSC) spectroscopy have been recorded in 25 μm thick samples of pristine polycarbonate (PC) and zinc oxide nano particle-filled polycarbonate. Polycarbonate (PC)/zinc oxide (ZnO) nanocomposites of different mass ratio (e.g., 1, 3, and 5%) were prepared by sol–gel method, followed by film casting. The glass transition temperature of nanocomposite samples increases with increase in concentration of ZnO nano fillers. It is due to the strong interaction between inorganic and organic components. The TSC peaks of nanocomposite and pristine PC indicate the multiple relaxation process. It has been observed that the magnitude of TSC decreases with increase in concentration of nanofillers. The TSC characteristics of 5% filled nanocomposites shows exponential increase of current at higher temperature region. This increase in current is caused by formation of charge-transfer complex between inorganic phase (e.g., ZnO) and organic phase (e.g., PC). Thus, the nano material like zinc oxide transfers the charge carriers from inorganic phase to organic phase rapidly and resultant current increases exponentially. This current is known as leakage current or breakdown current. TSC peak height is observed as a function of the polarizing field. The height of TSC peak increases as the field increases in pristine PC, while TSC peak height is suppressed in nanocomposite samples. This indicates the amount of space charge is smaller in the nanocomposites with a proper addition of ZnO nano fillers than in the pristine PC.     

AFM,ellipsometry, XPS and TEM on ultra-thin oxide/polymer nanocomposite layers in organic thin film transistors

Here we report on the fabrication and characterization of ultra-thin nanocomposite layers used as gate dielectric in low-voltage and high-performance flexible organic thin film transistors (oTFTs). Reactive sputtered zirconia layers were deposited with low thermal exposure of the substrate and the resulting porous oxide films with high leakage currents were spin-coated with an additional layer of poly-α-methylstyrene (PαMS). After this treatment a strong improvement of the oTFT performance could be observed; leakage currents could be eliminated almost completely. In ellipsometric studies a higher refractive index of the ZrO₂/PαMS layers compared to the “as sputtered” zirconia films could be detected without a significant enhancement of the film thickness. Atomic force microscopy (AFM) measurements of the surface topography clearly showed a surface smoothing after the PαMS coating. Further studies with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) also indicated that the polymer definitely did not form an extra layer. The polymer chains rather (self-)assemble in the nano-scaled interspaces of the porous oxide film giving an oxide–polymer “nanocomposite” with a high oxide filling grade resulting in high dielectric constants larger than 15. The dielectric strength of more than 1 MV cm⁻¹ is in good accordance with the polymer-filled interspaces.     

Effect of ionic conductivity of a PAN–PC–LiClO<Subscript>4</Subscript> solid polymeric electrolyte on the performance of a TiO<Subscript>2</Subscript> photoelectrochemical cell

A nanoparticle TiO₂ solid-state photoelectrochemical cell has been fabricated. The effect of ionic conductivity of a solid electrolyte of polyacrylonitrile (PAN)–propylene carbonate (PC)–lithium perchlorate (LiClO₄) on the performance of a photoelectrochemical cell of indium tin oxide (ITO)/TiO₂/PAN–PC–LiClO₄/graphite has been investigated. A nanoparticle TiO₂ film was deposited onto ITO-covered glass substrate by controlled hydrolysis technique. A solid electrolyte of PAN–LiClO₄ with PC plasticizer prepared by solution casting technique was used as a redox couple medium. The room temperature conductivity of the electrolyte was determined by AC impedance spectroscopy technique. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows a photovoltaic effect under illumination. The short-circuit current density, J _sc, and open-circuit voltage, V _oc, vary with the conductivity of the electrolyte. The highest J _sc of 2.82 μA cm⁻² and V _oc of 0.56 V were obtained at the conductivity of 4.2 × 10⁻⁴ Scm⁻¹ and at the intensity of 100 mW cm⁻².     

Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Formation and dielectric properties of anodic oxide films on Zr–Al alloys

Zr–Al alloys containing up to 26 at.% aluminum, prepared by magnetron sputtering, have been anodized in 0.1 mol dm⁻³ ammonium pentaborate electrolyte, and the structure and dielectric properties of the resultant anodic oxide films have been examined by grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and AC impedance spectroscopy. The anodic oxide film formed on zirconium consists of monoclinic and tetragonal ZrO₂ with the former being a major phase. Two-layered anodic oxide films, comprising an outer thin amorphous layer and an inner main layer of crystalline tetragonal ZrO₂ phase, are formed on the Zr–Al alloys containing 5 to 16 at.% aluminum. Further increase in the aluminum content to 26 at.% results in the formation of amorphous oxide layer throughout the thickness. The anodic oxide films become thin with increasing aluminum content, while the relative permittivity of anodic oxide shows a maximum at the aluminum content of 11 at.%. Due to major contribution of permittivity enhancement, the maximum capacitance of the anodic oxide films is obtained on the Zr–11 at.% Al alloy, being 1.7 times than on zirconium at the formation voltage of 100 V.     

Dilectric and thermal properties of PEO doped with cadimium chloride salt

The main aim of this research is to investigate the effect of salt concentration on the dielectric properties(AC (σ_AC),permittivity（ε′）,dielectric loss（ε″）,and dielectric relaxation process) and melting behavior of polyethylene oxide （PEO）/CdCl₂ complexes.The dielectric study was carried out over a frequency range 10-335 kHz and a temperature range 25-45℃.The AC conductivity,permittivity and dielectric loss of the PEO/CdCl₂ complexes increase with increasing salt concentration and temperature.Also,it was found that the addition of CdCl₂ salt to PEO host reduced the melting temperature of PEO host.Dielectric results reveal that the relaxation process of these complexes is due to viscoelastic relaxation or non-Debye relaxation at room temperature.Additionally,it was found that relaxation behavior remained viscoelastic at different temperatures and salt concentrations.     

Experimental study of the influence of solvent and asphaltenes on liquid–solid phase behavior of paraffinic model systems by using DSC and FT-IR techniques

This experimental work presents the results of a study about the liquid–solid phase behavior of high molecular weight n-paraffins (C₂₄–C₂₈ mixture and C₃₆ pure) in aliphatic (n-decane and squalane) and aromatic (xylene and 1-phenyl dodecane) solvents. The effect of asphaltenes of different chemical nature over the liquid–solid behavior of heavy n-paraffins is also studied. Differential Scanning Calorimetry (DSC) was used to obtain the phase transitions onsets and enthalpies as well as the wax solubility curves. Crystallinity was studied by using both DSC and Infrared Spectroscopy (FT-IR) techniques. The results obtained and presented in this study showed that both, solvent and asphaltenes as well as their chemical nature have a significant effect on paraffin crystallization process.     

Optical and dielectric characteristics of photochromic hybrid sol-gel materials

Photochromic silica based organic-inorganic hybrid materials containing covalently linked cyanoazobenzene chromophores were investigated by optical and dielectric spectroscopy. These materials, obtained via sol-gel process, were deposited onto glass substrates by spin coating technique to achieve thin transparent films. To investigate photoinduced alignment, the UV-Vis absorption spectra of the sol-gel films were recorded under illumination with linearly polarized blue light. Dielectric relaxation spectroscopy revealed a variety of relaxation processes: the α-process related to the dynamic glass transition temperature located around 150°C, and an Arrhenius-type β-relaxation (activation energy 58–60 kJ/mol) that was assigned to orientational fluctuations involving the azobenzene group. The correspondence between dielectric and photochemical behavior was discussed.     

Novel soluble aromatic poly(amideimide)s containing 9,9-diphenylfluorene moieties: characterization and optical properties

A series of aromatic poly(amideimide)s containing 9,9-diphenylfluorene moieties and the amide units in the main chain have been synthesized by solution polycondensation reaction of newly prepared diamidedianhydride with several aromatic diamines: 1,3-phenylenediamine, 3,3′-dimethoxy-biphenyl-4,4′-diamine, 4,4′-oxydianiline, 4,4′-(1,3-phenylenedioxy)dianiline, 4,4′-(9-fluorenylidene)dianiline and 1,5-diaminonaphthalene. Molecular structures of the polymers obtained have been characterized using ¹³C NMR, ¹H NMR and FTIR spectroscopies. The polymers prepared are readily soluble in aprotic polar solvents, and form optically transparent films by solution casting. The resultant poly(amideimide)s have been analyzed by differential scanning calorimetry (DSC), thermogravimetry (TG) and wide-angle X-ray diffraction measurements. They exhibited high levels of thermal stability, with decomposition temperatures in the range 452–494 °C, and high glass transition temperatures (181–278 °C). The optical behavior of these polymers has been investigated in NMP solution as well as in the films. The photoluminescence (PL) spectra of the free-standing films prepared from the poly(amideimide)s exhibited maximum emission bands around 506–525 nm in the green region.     

Kinetics of oxide growth and oxygen evolution on p-Si in neutral aqueous electrolytes

The growth of thin oxide films on wafers of p-Si, (100) orientation, was studied in neutral and acidic aqueous solutions up to 10 V by microelectrochemical (cyclic voltammograms and current transient of potential steps) and microellipsometric measurements. The oxidation occurs according to the high-field law with high-field parameters log(i ₀/A cm^–2)=–13.4±1 and β=10.6±0.1 nm V^–1. The oxide films represent an almost ideal dielectric material with ε=6.5. Oxide growth is not affected by oxygen evolution, which starts at potentials >3 V. The electron transfer process was analysed in relation to the oxygen evolution reaction. Owing to the presence of oxide thicknesses higher than 2 nm at this point, direct tunneling is less probable and a tunneling via traps should be assumed for the charge transfer. Evidence for coupled electronic and ionic conduction is presented. A contribution of the valence band in SiO₂ is stated for the corrosion of oxides at potentials >4.5 V. Electronic Publication     

Vascular endothelial and smooth muscle cell culture on NaOH-treated poly(epsilon-caprolactone) films: a preliminary study for vascular graft development

Tissue engineering offers the potential of providing vessels that can be used to replace diseased and damaged native blood vessels. The endothelization of a synthetic vascular graft minimizes the failures associated with blood clotting and platelet activation. The aim of this study was to culture vascular-derived endothelial and smooth muscle cells on both untreated and NaOH-treated poly(epsilon-caprolactone) (PCL) films, a biocompatible and bio-resorbable polymer, and to evaluate the behavior of both cell types as a preliminary study for vascular graft development. PCL films were prepared by hot pressing; characterized by DSC, IR, SEM, and scanning force microscopy; and treated with NaOH to increase the surface hydrophilicity before cell culture. Endothelial and smooth muscle cells, isolated from pig cava vein, were characterized by immunofluorescence and confocal microscopy studies of endothelial nitric oxide synthase and alpha-smooth muscle actin. Good adhesion, growth, viability and morphology of both the endothelial and smooth muscle cells on PCL films were obtained, but a light stimulation of mitochondrial activity was observed during short culture times. NaOH treatment improved the adhesion and enhanced the proliferation in both cell types. This verified the possible use of this modified polymer as a support in the preparation of a synthetic vascular graft. [Diagram: see text] SEM micrograph of smooth muscle cells cultured on NaOH-treated PCL film. (Original magnification: 1000x).     

Disruption of lipid rafts impairs the production of nitric oxide in lipopolysaccharide-stimulated murine RAW264.7 macrophages

Upon stimulation with lipopolysaccharide, murine RAW264.7 macrophages generated a high amount of nitric oxide. Pretreatment of macrophages with methyl-β-cyclodextrin, which disrupted the lipid raft microdomains of the plasma membrane, inhibited the generation of nitric oxide by down-regulating the expression of inducible nitric oxide synthase. Methyl-β-cyclodextrin exposure significantly inhibited the degradation of IκB-α, blocked the translocation of p65/RelA into the nuclei and prevented the activation of the NF-κB signaling pathway. The results suggest that the expression of inducible nitric oxide synthase and the consequent production of nitric oxide depend on the integrity of the lipid rafts.     

Surface reactivity of polypyrrole/iron-oxide nanoparticles: electrochemical and CS-AFM investigations

Composite materials based on iron-oxide nanoparticles (magnetite, hematite, and maghemite) and tetraoxalate-doped polypyrrole (PPy) were electrochemically generated from aqueous solutions. Their composition was determined using electrochemical quartz crystal microbalance experiments. The oxide percentage in mass was found to vary from 17 to 27% depending on the oxide identity. They were all shown to be fascinating candidates as protective materials against corrosion of iron and carbon steel materials although maghemite-nanoparticle-loaded polypyrrole films offer the best performances. An anionic surfactant (sodium dodecylsulfate) was added to the electrodeposition solution to avoid the formation of clusters. These anions were also shown to improve the conductivity of the resulting PPy films, while the presence of oxide nanoparticles tends to decrease this same surface conductivity. On the other hand, the correlation between the morphology and the local conductivity appears to be more obvious in the absence of anionic surfactants than in their presence. This aspect is discussed although it still needs further investigation. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Flow injection measurements of <Emphasis Type="Italic">S</Emphasis>-nitrosothiols species in biological samples using amperometric nitric oxide sensor and soluble organoselenium catalyst reagent

A novel flow injection analysis (FIA) system suitable for measurement of S-nitrosothiols (RSNOs) in blood plasma is described. In the proposed (FIA) system, samples and standards containing RSNO species are injected into a buffer carrier stream that is mixed with the reagent stream containing 3,3′-dipropionicdiselenide (SeDPA) and glutathione (GSH). SeDPA has been shown previously to catalytically decompose RSNOs in the presence of a reducing agent, such as GSH, to produce nitric oxide (NO). The liberated NO is then detected downstream by an amperometric NO sensor. This sensor is prepared using an electropolymerized m-phenylenediamine (m-PD)/resorcinol and Nafion composite films at the surface of a platinum electrode. Using optimized flow rates and reagent concentrations, detection of various RSNOs at levels in the range of 0.25–20 μM is possible. For plasma samples, detection of background sensor interference levels within the samples must first be carried out using an identical FIA arrangement, but without the added SeDPA and GSH reagents. Subtraction of this background sensor current response allows good analytical recovery of RSNOs spiked into animal plasma samples, with recoveries in the range of 90.4–101.0%.