Thermal behavior and signature patterns of human cytokine and soluble cytokine receptors investigated using dielectric thermal analysis and thermogravimetry

Cytokines are small regulatory proteins secreted mostly by cells of the immune system. Cytokines participate in anti-inflammatory and pro-inflammatory processes in the body and in responses to host exposure to pathogens. In this study, the thermal behavior of human recombinant cytokines and soluble cytokine receptors; IFNγ, TNFα, IL-1 receptor antagonist, soluble TNF-receptor types 1 and 2, and sIL-2 receptor α were analyzed by dielectric thermal analysis at 37 °C and by thermogravimetry. Measurements were performed at a frequency range of 0.1–300,000 Hz. Permittivity and loss factor measurements were used to calculate mobility of charges (tan δ values) in the proteins from Debye plots. Peak frequencies and polarization times were used to determine dielectric signatures for each cytokine and receptor. Peak frequencies and polarization times were obtained for each cytokine and receptor analyzed. Detection of unique dielectric signatures of the proteins will aid development of sensitive dielectric sensors capable of detecting cytokines and soluble cytokine receptors in various human samples for malaria diagnosis.     

Human cytokines characterized by dielectric thermal analysis, thermogravimetry, and differential scanning calorimetry

Malaria affects over 500 million people worldwide leading to 1–2 million deaths each year, the majority of whom are children. Four Plasmodium species cause malaria in humans. To properly diagnose, and correctly treat malarial infections, accurate diagnosis of infection is required. Proper diagnosis of infection will result in a reduction of morbidity, mortality, and of drug resistant parasites. However, the current tests for malaria diagnosis do not efficiently identify the appropriate human and parasite biomarkers associated with disease. Detection of specific inflammatory mediators such as cytokines associated with malaria pathogenesis will aid the determination of disease progression, disease prognosis, and the early diagnosis of malaria infection. In this study, we used dielectric thermal analysis (DETA), thermogravimetric analysis, and differential scanning calorimetry (DSC) to characterize five human cytokines (IL-1α, IL-2, IL-4, IL-6, and IL-10), to demonstrate how their thermoanalytical properties can be investigated for sensor design. Analysis for DETA was performed at a frequency range of 0.1–300,000 Hz. Permittivity and loss factor measurements were used to calculate tan δ values. Peak frequencies were used to determine dielectric signatures for each cytokine. The peak frequencies were different for each cytokine analyzed. In addition, activation energies were frequency dependent for IL-2 but frequency independent for the remaining four cytokines. Cytokines were also examined using DSC which established variance in heat of crystallization and heat of fusion of solvent among the five cytokines. A noticeable differentiation was observed with IL-1α among the other four cytokines when analyzed using trend analysis. Detection of unique dielectric signals will aid development of sensitive dielectric sensors capable of detecting cytokines in various human samples.     

Structural,dielectric and electrical properties of zinc doped nickel nanoferrites prepared by simplified sol–gel method

Zinc doped nickel ferrite nanoparticles having the general formula Ni_1−xZn_xFe₂O₄ (x = 0.1, 0.2, 0.3, 0.4, 0.5) were prepared with simplified sol–gel method. The structural and dielectric properties of these samples sintered at 750 ± 5 °C were studied. X-ray diffraction patterns confirm the single phase spinel structure for prepared samples. The scanning electron microscope images indicated that the particle size of the samples lies in the nanometer regime. The dielectric constant (ε_r) and dielectric loss tangent (tan δ) of nanocrystalline nickel ferrites were investigated as a function of frequency and Zn concentration. The dependence of ε_r and tan δ on the frequency of the alternating applied electric field is in accordance with the Maxwell–Wagner model. The prepared samples have a lowest dielectric constant compared to the already reported samples of the same composition to the best of our knowledge. The effect of Zn doping on the dielectric properties of nickel ferrites is explained on the basis of cations distribution in the crystal structure.     

Effects of thermal history on solid state and melting behavior of amino acids

Dielectric Thermal Analysis (DETA) of drugs, proteins and amino acids reveals a strongly linear conductivity increase prior to and peaking at the melt, associated with dielectric viscoelastic properties of the material. Premelt onset and peak are shown to depend on thermal history. Comparisons of neat amino acid samples to samples heated to 150 °C; dried in a desiccator; or heated above their melting point and cooled show significant premelt and melt shifts. Melts are also correlated with phase transitions observed by Differential Scanning Calorimetry (DSC). Activation energies attributed to charging in the premelt for amino acids were typically 250 J/mole.     

Electrical behaviour of butyl acrylate/methyl methacrylate copolymer films irradiated with 1.5 MeV electron beam

Electrical conductivity and dielectric parameters of the (BuA/MMA) copolymer films irradiated with 1.5 MeV electron beam (EB) have been studied. The samples were irradiated with different doses of the electron beam: 5, 10, 50, 125 and 200 kGy. The electrical conductivity of the samples was found to decrease as the irradiation dose increases. The temperature dependence of the direct current (dc) conductivity for unirradiated and irradiated samples has been obtained over a temperature range from 293 to 373 K. The activation energy values were calculated for all samples. Moreover, measurements of the dielectric constant, dielectric loss and alternating current (ac) conductivity were performed at a frequency range from 100 Hz to 5 MHz at room temperature. The results indicated that the EB irradiation has formed some traps in the energy gap, which reduce the movement of the charge carriers. Furthermore, a direct proportional relationship between the activation energy and the irradiation dose was estimated in two regions: below and above the glass transition temperature of the polymer. Dipole relaxation was observed in the samples, and the dose effect was found to shift this relaxation towards higher frequencies.     

Dielectric relaxation processes and ionic conduction behaviour in poly(ethylene oxide)–montmorillonite clay nanocomposite aqueous colloidal suspensions

The relative complex dielectric function, electric modulus, alternating current (ac) electrical conductivity and complex impedance spectra of poly(ethylene oxide) (PEO)–montmorillonite (MMT) clay aqueous colloidal suspension (hydrocolloids) were investigated over the frequency range 20 Hz to 1 MHz at 27 °C. The relaxation time corresponding to electrode polarisation and Maxwell–Wagner polarisation processes (ionic conduction) were determined from these plots. The direct current (dc) electrical conductivity is evaluated from the fitting of real part ac conductivity data to the Jonscher power law. A correlation of increase in dc conductivity and decrease of ionic conduction relaxation time with increase of clay concentration is discussed considering intercalation of PEO chains and its dynamics and exfoliation of MMT clay nanoplatelets in these complex fluids. The formation of PEO–MMT clay supramolecular lamellar nanostructures with increase in continuity of lamellae arrangements were explored for the structural conformation of these nanocomposite novel materials.     

Bi3+/Ce3+ doped ZnO nanoparticles with enhanced photocatalytic and dielectric properties

In this study, varying % Bi-doped on 1% Ce-doped ZnO (1CZ) nanoparticles (X% B-1CZ) were synthesized via a facile, simple, low-cost, sol–gel process. Various characterization techniques were employed to characterize the synthesized compound, while the dielectric properties i.e. dielectric constant, dielectric loss and AC conductivity against frequency were studied with the help of a precision impedance analyzer. It was observed that by increasing bismuth content in the nanoparticles, the dielectric constant also increased in the range (1.47 × 10⁶ – 4.02 × 10⁶) at 20 Hz, and vice versa for dielectric loss decreased from 1.05 × 10⁶ to 0.39 × 10⁶. The role of prepared compounds as photocatalysts was also investigated against methylene blue under ultraviolet irradiation. The degradation efficiency, as well as the dielectric properties of 7% Bi-doped on 1% Ce-doped ZnO (7%B-1CZ), were found to be the best. Overall, it was found that the synthesized compounds proved promising candidates with enhanced photocatalytic & dielectric properties and hence could safely be employed for environmental remediation purposes and energy storage devices.     

Electrical and electrochemical studies on magnesium ion-based polymer gel electrolytes

The development of polymer gel electrolyte system with high ionic conductivity is the main objective of polymer research. Electrochemical devices based on lithium ion-conducting polymer electrolyte are not safe due to the explosive nature of lithium. An attempt has been made to synthesize magnesium ion-conducting polymeric gel electrolytes, poly (vinylidene fluoride-co-hexafluoropropylene)–propylene carbonate–magnesium perchlorate, PVdF(HFP)-PC–Mg(ClO₄)₂ using standard solution-cast techniques. The maximum room temperature ionic conductivity of the synthesized electrolyte system has been observed to be 5.0 × 10⁻³ S cm⁻¹, which is quite acceptable from a device fabrication point of view. The temperature-dependent conductivity and the dielectric behavior were also analyzed. The pattern of the temperature-dependent conductivity shows the Arrhenius behavior. The dielectric constant ε _r and dielectric loss ε _i increases with temperature in the low-frequency region but almost negligible in the high-frequency region. This behavior can be explained on the basis of electrode polarization effects. The real part M _r and imaginary part M _i versus frequency indicate that the systems are predominantly ionic conductors. Further, the synthesized electrolyte materials have been checked for its suitability in energy storage devices namely redox supercapacitor with conducting polymer polypyrrole as electrode materials, and finally, it was observed that it shows good capacitive behavior in low-frequency region. Preliminary studies show that the overall capacitance of 22 mF cm⁻² which is equivalent to a single electrode specific capacitance of 117 F gm⁻¹ was observed for the above said supercapacitors.     

Microwave dielectric properties of aqueous potassium iodide solutions as a function of temperature

The complex dielectric permittivity of aqueous KI solutions was studied for molalities of 0.50–4.01 m and temperatures of 288–323 K in the region of water dielectric permittivity dispersion. The values of high-frequency of dielectric permittivity (ε) and dielectric losses (ε″) were obtained at seven frequencies ranging between 7.5 and 25 GHz. The low-frequency electrical conductivity of the aforementioned solutions was measured for calculating ionic losses. A single relaxation process is observed in these solutions, fitted by the Debye or Cole-Cole equation with small distribution parameters. The static dielectric constant and dielectric relaxation time were studied as functions of temperature and concentration; the activation enthalpy of dielectric relaxation was calculated. The temperature dependence of the static dielectric constant was found to disappear in highly concentrated solutions. The structure-breaking effect on water caused by K⁺ and I⁻ ions was affirmed, this effect disappearing in going to elevated temperatures.     

Dielectric spectroscopy of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) films

In this paper, we report a systematic study of the dielectric relaxation spectroscopy of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) polyester which has potential applications as a “green” dielectric material in electronic devices. The dielectric spectra was measured over a wide frequency range (10⁰ ～ 10⁷ Hz) from ?100 to 60 °C. A glass and a sub-glass transition relaxations were observed in the dielectric spectra of PHBHHx. In addition, a nearly constant loss behavior was found by analyzing the dielectric and conductivity spectra.     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.     

Epoxy nanocomposites with high thermal conductivity and low loss factor: Realize 3D thermal conductivity network at low content through core-shell structure and micro-nano technology

Dielectric polymers with high thermal conductivity are very promising in the fields of aerospace and electronic device packaging. However, composites with excellent dielectric properties usually have low thermal conductivity. It is usually to fill the polymer with thermal conductivity particles to improve the thermal conductivity, but the high content of filler often reduces the mechanical properties of the polymer. In this paper, the traditional insulating polymer epoxy resin was used as the matrix, by covering the surface of silicon carbide with graphene to form a core-shell structure and co-filled with nano diamonds to achieve the preparation of high-performance epoxy resin at low content. The results showed that at the filling content of 30 wt%, the thermal conductivity of epoxy nanocomposites showed a dramatic thermal conductivity enhancement of 1263%, the energy storage modulus increased by 1.1 GPa, and the dielectric loss remained unchanged at 50 Hz. The advantages of the composite are the structural design and surface modification of the filler, which not only take advantage of its inherent advantages, but also improve the interface area with the epoxy matrix. The composite materials with excellent properties are expected to provide theoretical guidance for the application of high thermal conductivity dielectric materials.     

Dielectric and impedance properties of Sr(Sm0.5Nb0.5)O3 ceramics

Perovskite types Sr(Sm_0.5Nb_0.5)O₃, (SSN) ceramics have been prepared through solid state reaction route. The scanning electron microscopy provides information on the quality of the samples and uniform grain distribution over the surface of the samples. The field dependence of the dielectric response was measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 60 °C to 420 °C indicates polydispersive nature of the materials. An analysis of the dielectric constant (?′) and tangent loss (tanδ) with frequency is performed assuming a distribution of relaxation times as confirmed by the scaling behavior of electric modulus spectra. The frequency dependence of the electric modulus peak is found to obey Arrhenius law with activation energy of ∼0.026 eV. The complex plane impedance plot shows the grain boundary contribution for higher value of dielectric constant in the law frequency region. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures in SSN.     

Thermal and electrical relaxation studies in Li(4+x)TixNb1−xP3O12 (0.0 ≤ x ≤ 1.0) phosphate glasses

A new superionic conducting transparent phosphate glasses with composition Li_(4+x)Ti_xNb_1?xP₃O₁₂ (0 ≤ x ≤ 1.0) were prepared by rapid melt quenching. As quenched samples were characterized by X-ray powder diffraction, differential scanning calorimetric and Fourier transform infrared spectroscopy studies. These glasses were found to have high thermal stability parameter and Li₄NbP₃O₁₂ has been found to have high glass forming ability. Electrical properties of the present glasses were studied by impedance and dielectric spectroscopy in the frequency range 10 Hz–3 MHz in the temperature range 323–523 K. Arrhenius behavior has been observed for all the glass in conductivity, dielectric loss and conductivity relaxation and their activation energies are explained and reported.     

Dielectric behavior of polyaniline synthesized by different techniques

Polyaniline doped with dodecylbenzenesulfonic acid (Pani.DBSA) was synthesized by different procedures: by a dedoping-redoping process, by one step inverted emulsion polymerization and by one step aqueous dispersion polymerization. The effect of these different techniques on the electric properties (dielectric constant, dielectric losses, and complex electric modulus) of the corresponding emeraldine base has been studied by thermal dielectric analyzer (DETA) in the temperature range −130 °C to 200 °C and in frequency range 0.03-10⁵ Hz. It was found that the preparation technique has significant influence on the dielectric properties of Pani. The different synthetic routes give rise to polyaniline with different distribution of electric relaxation process, indicating different chain structure. Emeraldine base from Pani.DBSA prepared by one step aqueous dispersion polymerization exhibits one single relaxation peak with narrow distribution whereas that prepared by inverted emulsion polymerization exhibits two relaxation peaks, indicating two-phase structure as indicated by a bimodal distribution of relaxation process. Emeraldine base from Pani.DBSA prepared by dedoping-redoping process presents an intermediary behavior. Percentage crystallinity of Pani.DBSA samples has also been investigated using wide-angle X-ray diffraction analysis. Pani.DBSA prepared by aqueous dispersion exhibited higher crystallinity degree, which agrees with the higher conductivity.     

Pyrolysis of N-doped organic aerogels with relation to sorption properties

Resorcinol–formaldehyde aerogels (five samples, three of them with addition of nitrogen containing precursors—3-hydroxypyridine, 3-aminophenol and melamine) have been prepared by sol–gel polycondensation, subcritical drying and pyrolysis. The pyrolysis of prepared organic aerogels has been studied by non-isothermal TG at constant heating rate. The process of pyrolysis has been found to consist of three steps with the total mass loss 40.2–61.7% (room temperature—1,000 °C). The resulted carbon aerogels have been tested as sorbents of Ni(II), Pb(II) and Cu(II) ions from aqueous solutions. Various relations have been found among the results obtained from the pyrolysis experiments and properties affecting adsorption. Besides the expected correlation between the mass loss gained from TG (isothermal step at 500 °C was applied) and from heating in the laboratory oven, the relationship between the mass loss during pyrolysis and sorption capacities for all three metal ions has been found. Other relations among pyrolysis behaviour, surface area and content of nitrogen have been also examined. Batch adsorption experiments show (with an exception of one sample) that N-doped samples have higher adsorption capacity for metal ions. In addition, changing of nitrogen functionalities during the pyrolysis has been considered and pyridinic-N (N-6) functionality has been contemplated as a suitable structure for the adsorption process.     

A study of thermal and dielectric behavior of manganese malonate dihydrate single crystals

Thermal decomposition of manganese malonate dihydrate single crystals grown by gel method has been studied using the TG-DTA and DSC techniques. The presence of water molecules and the dehydration stages are discussed. Dielectric constant, dielectric loss, and AC conductivity have been estimated as a function of temperature in the range of 40–120 °C for four different frequencies. Thermal studies reveal that the material is thermally stable up to123 °C. The dielectric measurements indicate that the dielectric parameters increase with the increase in temperature. Also, the dielectric constant and dielectric loss factor values decrease whereas the electrical conductivities increase with the increase in frequency of the AC applied.     

Catalytic effect of bases in impregnation of guanidine nitrate on Poplar (<Emphasis Type="Italic">Populus</Emphasis>) wood

Wood, one of the flammable material, was treated with aqueous solution of guanidine nitrate (GUN) and also with small amount of bases like N,N-dimethylformamide, 4-dimethylaminopyridine, pyridine, and triethylamine in the treating solution. These bases catalyze the impregnation of GUN as indicated by increase in mass gain percentage, elemental analysis, and scanning electron microscopy. To study their thermal behavior, dynamic thermogravimetry (TG) and derivative thermogravimetry (DTG) analysis under nitrogen atmosphere have been applied from ambient temperature to 973 K on all samples, at multiple linear heating rates 2.5, 5, 10, and 20 K min⁻¹. Non-isothermal, “model free” iso-conversional multiple heating rate methods, Ozawa–Flynn–Wall (O–F–W) and modified Coats–Redfern are used to calculate activation energy of samples. The activation energy of samples is found in the range 109–208 kJ mol⁻¹. Thermal parameters like overall pyrolysis duration, maximum mass loss rate, corresponding to DTG peak maximum and percentage char yield calculated at 873 K from TG curves are used to appraise the flammability of samples. Also, flammability of samples is determined by reliable methods namely limiting oxygen index and underwriters laboratories 94 (UL 94) test. The aforesaid study indicates that base catalyzed impregnated samples are less flammable than those impregnated with only GUN and untreated ones.     

Characterization of dental composites by thermal analysis, infrared spectroscopy and scanning electron microscopy

Commercial light-cured dental composites were used in this study. Two laboratorial composites, Resilab (Wilcos/Brazil), Epricord (Kuraray/Japan) were compared under cured and uncured conditions. Thermal analysis, infrared spectroscopy and scanning electron microscopy were used to evaluate the dental composites. The mass change and heat flow signals (TG–DSC) were recorded simultaneously by using STA 409 PC Luxx (NETZSCH), in the 25–800 °C temperature range at a heating rate of 10 °C/min under nitrogen atmosphere (70 mL/min). Employing thermo-microbalance TG 209 C F1 Iris (NETZSCH) coupled to the BRUKER Optics FTIR TENSOR, the samples were analyzed by combined thermogravimetric and spectroscopic methods (TG–FTIR). The initial sample mass was about ~12 mg, the data collection have been done in the 35–800 °C temperature range at a heating rate of 20 K/min in nitrogen atmosphere (flow rate: 40 mL/min). Finally, superficial topographic was analyzed by scanning electron microscopy (SEM). Dental composite evaluation suggests a high thermal stability and inorganic content in RES D sample. Degrees of conversion (DC) values were almost the same and there was no direct relationship between DC and amount of particles and size. Similar compositions were found in all samples.     

Dielectric studies of binary mixtures of n -propyl alcohol and ethylenediamine

Dielectric constant (ε’) and dielectric loss (ε") of n-propyl alcohol (PA), ethylenediamine (EDA) and their binary mixtures, for different mole fractions of ethylenediamine have been experimentally measured at 11.15 GHz microwave frequency. Values of density (ρ), viscosity (η) and square refractive index (n _D ² ) of binary mixtures as well as those of pure liquids are reported. Excess square refractive index, viscosity and activation energy of viscous flow have also been estimated. These parameters have been used to explain the formation of complexes in the system.