Molecular dynamics of amorphous pharmaceutical fenofibrate studied by broadband dielectric spectroscopy

Fenofibrate is mainly used to reduce cholesterol level in patients at risk of cardiovascular disease. Thermal transition study with the help of differential scanning calorimetry （DSC） shows that the aforesaid active pharmaceutical ingredient （API） is a good glass former. Based on our DSC study, the molecular dynamics of this API has been carried out by broadband dielectric spectroscopy （BDS） covering wide temperature and frequency ranges. Dielectric measurements of amorphous fenofibrate were per- formed after its vitrification by fast cooling from a few degrees above the melting point （Tm=354.11 K） to deep glassy state. The sample does not show any crystallization tendency during cooling and reaches the glassy state. The temperature dependence of the structural relaxation has been fitted by single Vogel- Fulcher-Tamman （VFT） equation. From VFT fit, glass transition temperature （Tg） was estimated as 250.56 K and fragility （m） was determined as 94.02. This drug is classified as a fragile glass former. Deviations of experimental data from Kohlrausch-Williams-Watts （KWW） fits on high-frequency flank of α-peak indicate the presence of an excess wing in fenofibrate. Based on Ngai＇s coupling model, we identified the excess wing as true Johari-Goldstein （JG） process. Below the glass transition temperature one can clearly see a secondary relaxation （γ） with an activation energy of 32.67 kJ/mol.

Dielectric Spectroscopy Study on Vesicles of CTAB/SDBS System

Amphiphilic molecules can form into different structures, such as micelle, microemulsion, vesicle, liposome, liquid crystals, and so on by self-associating. The Dielectric Spectroscopy (DS) method has been applied to the systems of micelle and microemulsion successfully. For the first time the author put the method to the system of vesicle of CTAB/SDBS. The experiments show clear dielectric relaxation and the results were discussed primarily.

Effects of heavy metal on dielectric properties of E. coli revealed by dielectric spectroscopy

Dielectric spectroscopy of E. coli cell before and after exposure to heavy metals Cd^2＋ , Cu^2＋ , Zn^2＋ and Ca^2＋ was investigated. The results indicate that changes in dielectric spectra reflect effects of heavy metal on the structure and function of E. coli cells. Heavy metal can change membrane capacitance as well as pennittivity and conductivity of the cytoplasm. Changes in volume fraction suggested that dielectric measurement could monitor the growth of E. coli cells. These results demonstrated that dielectric spectroscopy was a potential effective technique for studying electric properties of biological cells.

Determination of the oxidative stability of olive oil using an integrated system based on dielectric spectroscopy and computer vision

During storage,olive oil may suffer degradation leading to an inferior quality level when purchased and consumed.Oxidative stability is one of the most important parameters for maintaining the quality of olive oil,which affects its acceptability and market value.The current methods of predicting the oxidative stability of edible oils are costly and time-consuming.The aim of the present research is to demonstrate the use of dielectric spectroscopy integrated with computer vision for determining the oxidative stability index(OSI)of olive oil.The most effective features were selected from the extracted dielectric and visual features for each olive oil sample.Three machine learning techniques were employed to process the raw data to develop an oxidative stability prediction algorithm,including artificial neural network(ANN),support vector machine(SVM)and multiple linear regression(MLR).The predictive models showed a great agreement with the results obtained by the Rancimat instrument that was used as a reference method.The best result for modelling the oxidative stability of olive oil was obtained using SVM technique with the R-value of 0.979.It can be concluded that this new approach may be utilized as a perfect replacement for quicker and cheaper assessment of olive oil oxidation.

Dielectric spectroscopy as a potential technique for prediction of kiwifruit quality indices during storage

Dielectric spectroscopy has been employed as a simple,low cost and a non-destructive way for prediction of some physicochemical indices of kiwifruit during storage.A parallel-plate capacitor was developed and supplied with sinusoidal voltage waves within a frequency range of 40 kHz–20 MHz.Dielectric properties of samples were measured by the dielectric sensor.Additionally,changes associated with fruit ripening properties,including firmness,total soluble solid(TSS)and pH were determined as a function of time at 2
C.The results showed that storage time significantly affected the quality characteristics of kiwifruit.Artificial neural networks(ANNs)were employed to develop models for prediction of quality indices from dielectric properties at the swept frequencies.Dielectric property features were selected as inputs while the quality indices including firmness,TSS and pH were chosen as output for the ANNs.The obtained models were able to predict the firmness,soluble solids content,and pH of kiwifruit non-destructively.Among predictive models,an ANN with a topology of 20-19-1 gave a perfect capability to predict the kiwifruit firmness with R2 value of 0.92.Results of this research show that this technique can be used as an efficient and non-destructive method for kiwifruit quality evaluation and monitoring the ripening.

Piezoresponse force microscopy and dielectric spectroscopy study of Ba_(0.6)Sr_(0.4)TiO_(3)thin films

Research on synthesis,characterization and determination of processing-structure-property relationships of commercially important ferroelectric thin films has been performed.The sol-gel type solution deposition technique was applied to produce good quality thin films of Ba_(0.6)Sr_(0.4)TiO_(3)(BST60/40)chemical composition on the stainless steel substrates.The thin films were characterized in terms of their microstructure,crystal structure,phase composition,piezoelectric and dielectric properties.It was found that the BST60/40 thin film adopted the cubic structure at room temperature with an elementary cell parameter a-3:971e8TÅ.Morphology of the thin film surface was studied with Atomic Force Microscopy(AFM).Average roughness of the thin films surface was found(Sa=0:055μm).Piezoresponse Force Microscopy(PFM)was applied for the thin film characterization.Active piezoelectric regions were found in BST60/40 thin film.Therefore,dielectric response measured at room temperature was studied in assumption of piezoelectric electric equivalent circuit.

Dielectric spectroscopy of solid solutions based on sodium-potassium-cadmium in the temperature range (10 ÷ 900) K

This paper studies the dielectric spectra of solid solutions(SS)of the system(1−x−y)NaNbO_(3)-xKNbO_(3)-yCdNb_(2)O_(6) y=0.075,x=0.05÷0.30 in the temperature range(10÷900)K.The formation of a local maximum was established in the interval(260÷300)K at small x values,which,as KNbO3 increases,is gradually blurred and becomes an inflection point.Detected in SS with x=0.05÷0.10,the shift of the maxima of dependencesε′/ε_(0)(T)andε″/ε_(0)(T),depending on the frequency of the electric field at the temperature ranges(300÷304)K and(258÷271)K,is not related to relaxation.This anomaly may indicate a crystallographic disorder to A and B positions.The conclusion is made about the expediency of using the obtained results for the development of functional ferroactive materials.

Dielectric spectroscopy and structural characterization of nano-filler-loaded epoxy resin

This work outlines the characterization of epoxy resin[Bisphenol A-(epichlorhydrin):epoxy]and hardener[N(3-dimethylaminopropyl)-1,3-propylenediamine]with various inorganic nano-fillers.Dielectric characterizations of epoxy,hardener,neat epoxy(epoxy+hardener)and nano-epoxy(nano-filler+neat epoxy)composites loaded with 1 wt.%of inorganic nano-fillers(SiO_(2),Al_(2)O_(3),TiO_(2)and ZnO)were carried out using precision LCR meter,over the frequency range of 1 kHz-2 MHz at a constant temperature of 300.15 K.The structural information of nano-fillers,neat epoxy and nano-epoxy composites was understood by Fourier transform infrared spectroscopy and by XRD.Moreover,hardness and shear strength(shear punch)were also determined in order to gain additional information about the mechanical properties of epoxy composite.Influence of inorganic nano-fillers on the dielectric properties,structural chemistry and mechanical properties of neat epoxy composite is discussed thoroughly in this study.

An Investigation of Structure Transition in Sodium Dodecyl Trioxyethylene Sulfate/n-Butanol/n-Octane/Water System by Dielectric Relaxation Spectroscopy Method

The phase diagram of the quaternary system of sodium dodecyl trioxyethylene sulfate(SDES)/n-butanol/n-octane/water was obtained at (30.0±0.1) ℃. There exists a clear, isotropic, and low-viscosity L phase, which can be divided into W/O, bi-continuous(B.C.) and O/W microemulsions by conductivity measurement results. Dielectric Relaxation Spectroscopy(DRS) measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, dielectric parameters, phase parameters, etc., were applied to investigating the microstructures of the system mentioned above. For the samples with a fixed SDES/n-butanol mass ratio of 4/6 including 20%(mass fraction) of n-octane, DRS indicated a structure transition from a W/O to an O/W via a B.C. microemulsion with the increase of the water content. For the samples with a fixed (SDES/20%n-octane)/H_2O mass ratio of 5/5, DRS presented that there only exists a onefold structure of a W/O microemulsion as the (n-butanol/20%n-octane) content increases. The results obtained from DRS are in good agreement with those from the phase diagram.

Phase Behavior and Dielectric Spectroscopy of the Sodium Dodecyl Trioxyethylene Sulfate/n-Butanol/Water System

The phase diagram of the ternary system of sodium dodecyl trioxyethylene sulfate (SDES)/ n butanol/water is obtained at (30 0±0 1) ℃. There exists a clear, isotropic, and low viscosity L phase, which could be divided into W/O micelle, bi continuous (B.C.) phase and O/W micelle by conductivity measurements. Dielectric Relaxation Spectroscopy (DRS) measurements are applied to investigate microstructure changes of this system. For samples with a fixed weight ratio, SDES/ n butanol=3/7, DRS indicates a structure transition from W/O to O/W micelles via B.C. phase with the increase of water content. For the samples with a fixed weight ratio, SDES/H 2O=4/6, DRS can presents that there exist changes of onefold structure size of W/O micelles as n butanol content increases. The results obtained from DRS and their analyses are in good agreement with those from phase diagram and conductivity measurements.

Studies on the Phase Properties of Winsor Ⅰ-Ⅲ Type Microemulsions with Dielectric Relaxation Spectroscopy

The dielectric relaxation spectroscopy （DRS） of Winsor I -Ⅲ microemulsions for nonionic surfactant octyl polyglucoside CsG1.46/1-butanol/cyclohexanedwater system was studied. The experiment shows that the permittivity decreases with the increase in the frequency and clear dielectric relaxation phenomena were observed. Permittivity obviously decreases with the change of the microstructure of the microemulsion, W/O, B.C. and O/W can be distinguished by the permittivity.

Diagnostics of Argon Inductively Coupled Plasma and Dielectric Barrier Discharge Plasma by Optical Emission Spectroscopy

An experimental setup was built up to carry out radio frequency (RF) inductively coupled plasma (ICP) and dielectric barrier discharge (DBD), and to depict the optical emission spectra (OES) of the discharges. OES from argon ICP and DBD plasmas in visible and near ultraviolet region were measured. For argon ICP, the higher RF power input (higher than 500 W for our machine), the higher degree of argon plasma ionization. But that doesn't mean a higher mean electron energy. With the increase in the power input, the mean electron energy increases slightly, whereas the density of electron increases apparently On the contrary, argon DBD discharge behaves in the manner of a pulsed DC discharge on optical emission spectroscopy and V-I characteristics. DBD current is composed of a series of pulses equally spaced in temporal domain. The Kinetics of DBD emission strength is mainly governed by the frequency of the current pulse.

Dielectric Behavior of Middle Phase Microemulsion

Dielectric measurements were performed on middle phase microemulsions composed of sodium dodecylsulfate(SDS), cetyltrimethylammonium bromide(CTAB), n-butanol, n-heptane and brine. Distinct and unique dielectric behavior, with characteristic frequency dependence regularity on the salinity of the microemulsions, was observed in the low-frequency range from 10-10(3)Hz. It can be considered to be an interfacial polarization mechanism.

Dielectric properties and relaxation dynamics in PbF_2-TeO_2-B_2_O3-Eu_2O_3 glasses

Frequency and temperature dependent dielectric dispersion of 20PbF2？20TeO2？（60？x）B2O3？xEu2O3（x=0 to 2.5, mole fraction, %） glasses prepared by the melt？quenching technique were investigated in the frequency range 1 Hz？10 MHz and temperature range 313？773 K. Dielectric relaxation dynamics was analyzed based on the electric modulus behavior. Dielectric losses （tanδ） are found to be negligibly small in the temperature range 313？523 K, proving good thermal stability of the glasses. The present Eu2O3-doped oxyfluroborate glasses showed low dielectric loss at higher frequency and lower temperature, proving their suitability for nonlinear optical materials.

Dielectric properties of nucleated erythrocytes as simulated by the double spherical-shell model

The dielectric properties of nucleated erythrocytes from bullfrogs were measured in a frequency range of 10 kHz–110 MHz.The complex permittivity(ε*),complex conductivity(κ*),and complex resistivity(ρ*)were analyzed and compared in the 10.63%to 37.58%haematocrit(Hct)range.The relaxation behavior,the passive electrical properties,and the cellular structure parameters,including the cell membrane,the cytoplasm,the nuclear membrane,and the nucleoplasm of the nucleated erythrocyte suspensions were investigated.The method used is based on the binomial Cole–Cole equation and the double spherical-shell physical models.Upon the elimination of the electrode polarization effect,two definite relaxations related to the interfacial polarization are observed on low-and high-frequency dispersions.The permittivity values and the characteristic frequency values differ by one order of magnitude:the low-frequency relaxation increments[?ε1=(5.63±1.43)×103]and the characteristic frequency[fc1=(297.06±14.48)kHz]derived from the cell membrane,the high-frequency relaxation increments[?ε2=(5.21±1.20)×102]and the characteristic frequency[fc2=(3.73±0.06)MHz]derived from the dielectric response to the external electric field of the nuclear membrane,respectively.Moreover,the other core dielectric parameters,such as the relative permittivity of the cell membrane[εm=(7.57±0.38)]and the nuclear envelope[εne=(23.59±4.39)],the conductivity of the cytoplasm(hemoglobin,κHb=(0.50±0.13)S/m]and the nuclear endoplasm[κnp=(2.56±0.75)S/m],and the capacitance of the bilayer membranes[Cm:(0.84±0.04)μF/cm2],and Cne:(0.52±0.10)μF/cm2]were also accurately and reliably measured.This work presents a feasible method to evaluate the dielectric parameters and the cellular structure of the erythrocytes of bullfrogs.Moreover,it paves the way for new studies on the haematology of frogs and the detection of nucleated cells via dielectric impedance spectroscopy.

Dielectric Spectra of Aerosol OT/Water Systems at Different Concentrations and Temperatures

The dielectric spectra of aerosol OT[AOT, sodium（bis-2-ethylhexyl）sulfosuccinate]/water systems at different concentrations and temperatures were investigated by the dielectric relaxation spectroscopy（DRS）. Through the dielectric spectra of different concentrations, two dielectric relaxations were observed over a frequency range from 40 Hz to 110 MHz and the mechanisms of the relaxations were also interpreted based on the Grosse’s model. The low-frequency relaxation（around 105 Hz） was attributed to the radial diffusion of counterions along the long-half axis of the rod-like micelle, and the high-frequency relaxation（around 106 Hz） was ascribed to the radial diffusion of counterions along the short-half axis. Furthermore, specific emphasis was placed on studying the effects of temperature on system’s conductivity. It was observed that the low-frequency limit of conductivity（κl） decreased and then increased with the increment of temperature under the measured concentration. On the other hand, the conductivity（κm and κh） in meso- and high-frequency ranges always increased as temperature increased. Both the tendencies of alteration which mentioned above should be related to the phase transition of AOT/water system.

Comparison of Nitric Oxide Concentrations in μs-and ns-Atmospheric Pressure Plasmas by UV Absorption Spectroscopy

In this paper,an absorption spectroscopy measurement method was applied on two atmospheric pressure plasma sources to determine their production of nitric oxide.The concentrations are essential for evaluating the plasma sources based on the principle of the Dielectric Barrier Discharge（DBD）for applications in plasma medicine.The described method is based on a setup with an electrodeless discharge lamp filled with a mixture of oxygen and nitrogen.One of the emitted wavelengths is an important resonance wavelength of nitric oxide（λ = 226.2 nm）.By comparing the absorption behaviour at the minimum and maximum of the spectral absorption cross section of nitric oxide around that wavelength,and measuring the change in intensity by the absorbing plasma,the concentration of nitric oxide inside the plasma can be calculated.The produced nitric oxide concentrations depend on the pulse duration and are in the range of 180 ppm to 1400 ppm,so that a distance of about 10 cm to the respiratory tract is enough to conform to the VDI Guideline 2310.

Conformation and Counterion Distribution of Polyelectrolyte in Solution as Viewed from Dielectric Approach

Polyelectrolyte solutions are more variable than uncharged macromolecule due to electrical interaction between charged molecules and surrounding counterions.Therefore,the subject of polyelectrolyte solutions has attracted a wide range of interests in both basic and applied research,and has also been extensively explored.However,the understanding of the molecular dynamics and conformation of polyelectrolytes in solution remains to be deepened,and universal consensus on some key issues have not been reached.Many methods have contributed to solving the above problems in different ways,including dielectric relaxation spectroscopy(DRS).In this perspective,we briefly reviewed the history of dielectric spectroscopic research on polyelectrolyte solution,with emphasis on summarizing our efforts.In particular,we expound the characteristics of DRS and its ability to obtain the internal information of the system of interest.Finally,we evaluate the advantages and limitations of the dielectric method and discussed future prospects of this field.

Solvation Effects on the Dielectric Constant of 1 M LiPF6 in Ethylene Carbonate:Ethyl Methyl Carbonate 3:7

We report the dielectric constant of 1 M LiPF_(6)in EC:EMC 3∶7 w/w(ethylene carbonate/ethyl methyl carbonate)in addition to neat EC:EMC 3∶7 w/w.Using three Debye relaxations,the static permittivity value,or dielectric constant,is extrapolated to 18.5,which is compared to 18.7 for the neat solvent mixture.The EC solvent is found to strongly coordinate with the Li^(+)cations of the salt,which results in a loss of dielectric contribution to the electrolyte.However,the small amplitude and large uncertainty in relaxation frequency for EMC cloud definitive identification of the Li^(+)solvation shell.Importantly,the loss of the free EC permittivity contribution due to Li^(+)solvation is almost completely balanced by the positive contribution of the associated LiPF_(6)salt,demonstrating that a significant quantity of dipolar ion pairs exists in 1 M LiPF_(6)in EC:EMC 3∶7.

Dielectric,impedance,modulus spectroscopy and AC conductivity studies on novel organic ferroelectric diisopropylammonium chloride(dipaCl)

Organic molecular ferroelectric diisopropylammonium chloride(dipaCl)was successfully synthesized using diisopropylamine,hydrochloric acid(57%)and methanol solution.Dielectric permittivity,impedance,modulus spectroscopy and conductivity were systematically studied by Capacitance-Conductance(CP-G)measurements in the temperature range of 373-445 K.Dielectric property tests clearly show that the organic molecular ferroelectric dipaCl obeys Curies-Weiss law 1/e=(T-T0)/C.The real(Z′)and imaginary(Z″)parts of the electrical modulus were calculated from the various values of e′and e″.It is shown that AC conductivity satisfies the relation s(w)∞wn,where the power exponent n depends on temperature and frequency.From Arrhenius equation,the activation energies Es and Eh are also calculated which describes the complete conduction mechanism of dipaCl.