Investigation on third order nonlinear optical,electrical and surface properties of organic stilbazolium crystal of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate

The third order nonlinear optical, electric and dielectric properties of an organic stilbazolium derivative of 4-N,N-dimethylamino-N′-methylstilbazolium p-methoxybenzenesulfonate (DSMOS) crystal are reported. The nonlinear refractive index (n₂), two photon absorption coefficient (β) and third order optical susceptibility χ⁽³⁾ have been measured by Z-scan technique using Gaussian beam from the Nd:YAG laser at 1064 nm. The results show a large negative nonlinear refractive index (n₂ = −1.122 × 10−9 cm²/W) with a molecular two photon absorption coefficient β value of 3.625 × 10⁻⁶ cm/W. The low dielectric constant observed in the high frequency region indicates the suitability of the sample for electro-optic applications. The surface features are also investigated by atomic force microscopy (AFM).     

Structural,thermal, spectroscopic and magnetic studies of the (C2N2H10)0.5[FexV1−x(HPO3)2] (x = 0.26, 0.52, 0.74) solid solution

The (C₂N₂H₁₀)_0.5[Fe_xV_1−x(HPO₃)₂] (x = 0.26, 0.52 0.74) compounds have been obtained by mild solvothermal conditions in the form of micro-crystalline powder with brown color. The crystal structures were refined by X-ray powder diffraction data using the Rietveld method. The compounds crystallize in the monoclinic system, space group P2/c with the unit-cell parameters, a = 9.262(5) Å, b = 8.823(5) Å, c = 9.714(6) Å, β = 120.84(3)°; a = 9.245(1) Å, b = 8.823(1) Å, c = 9.698(1)Å, β = 120.80(1)° and, a = 9.254(4)Å, b = 8.822(4)Å, c = 9.702(4)Å, β = 120.73(3)° for (C₂N₂H₁₀)_0.5[Fe_0.26V_0.74 (HPO₃)₂] (1), (C₂N₂H₁₀)_0.5[Fe_0.52V_0.48(HPO₃)₂] (2), and (C₂N₂H₁₀)_0.5[Fe_0.74V_0.26(HPO₃)₂] (3). The compounds show an open crystalline structure with three-dimensional character, whose formula for the anionic inorganic skeleton is [M(HPO₃)₂]²⁻. The inorganic framework is formed by [MO₆] octahedra inter-connected by phosphite groups. The structure of the compounds exhibits channels extended along the [1 0 0] and [0 0 1] directions and the ethylendiammonium cations are located inside these channels, linked through hydrogen bonds and ionic interactions. The infrared spectra show the bands corresponding to the stretching (P–H) vibration of the phosphite group and the band corresponding to the deformation mode of the ethylendiammonium cation, δ(NH₃⁺). The thermal and thermodiffractometric behavior show that the compounds are stable up to approximately 300 °C, at higher temperatures the decomposition of the crystal structure by calcination of the organic cation starts. The diffuse reflectance spectra show bands of the V³⁺ ion (d²), and a band of the Fe³⁺ ion (d⁵), in a slightly distorted octahedral symmetry. The values of the Dq and Racah parameters (B and C) have been calculated for the V(III) cation. Magnetic measurements were performed on a powdered sample from 5 to 300 K at magnetic fields 1000, 500 and 100 G, in the ZFC and FC modes. At the magnetic field of 1000 G antiferromagnetic interactions were observed, but at 100 G have been detected higher values of the χ_m in the FC mode than those observed in the ZFC one, indicating the existence of a dominant ferromagnetic component at low temperature. The magnetization measurements show hystheresis loops at 5 K, with values of the remanent magnetization and coercive field of 1.91 emu/mol and 23 Gauss for (1), 25 emu/mol and 300 Gauss for (2), and 3 emu/mol and 50 Gauss for the compound (3).     

Temperature dependent transport properties in molybdenum oxide doped α-NPD

The temperature dependent transport properties of molybdenum oxide (MoO₃) doped N,N′-di(1-naphthyl)-N,N′-diphenylbenzidin (α-NPD) were studied over a frequency range of 100 Hz to 1 MHz. The value of trap density and mobility calculated by detailed analysis of current–voltage (I–V) characteristics are 9.43 × 10²⁶ m^?3 and 1.23 × 10^?6 cm² V^?1 s^?1, respectively. The relaxation time for the carriers in the bulk and in the interface region decreases with temperature. The Cole–Cole plot indicates the device can be modeled as the combination of two parallel resistor–capacitor (R–C) circuits with a series resistance of around 70 Ω. The dc conductivity shows two different regions in the studied temperature range with activation energy of E_a ～ 0.107 eV (region I) and E_a ～ 52 meV (region II), respectively. The ac conductivity follows the universal power law and the onset frequency increases with increase of temperature. The temperature dependent conduction mechanism can be explained by correlated hopping barrier (CBH) model.     

Magnetodielectric composite with ferrite inclusions as substrates for microstrip patch antennas at microwave frequencies

A study has been conducted to estimate the complex permittivity and permeability along with magnetic characterization of different volume fractions of magnetodielectric composites with cobalt ferrite nano inclusions. Using an in touch superstrate technique dielectric properties are estimated. Cavity perturbation technique is used to study the complex permeability of the samples. 4πM_s value and coercivity is measured using vibrating sample magnetometry. Structural and surface morphologies on the composite samples are conducted to determine the size and homogeneous distribution of nano inclusions. The average grain size of cobalt ferrite nanoparticles is found to be ～10 nm. The real part of permittivity and permeability of the samples varies from ～1–2.905 to ～1.01–1.05 with increase in inclusion content from 1% VF to 5% VF, respectively. The tan δ of permittivity and imaginary part of permeability is found to be of the order of ～10^?3 and ～10^?1 respectively. Verification of these composites as potential substrates for microstrip patch antenna is carried out by fabricating simple rectangular patch at 9.5 GHz using transmission line model. Rectangular patch is designed on 5% VF composite system. The return loss for the composite system was found to be ～?19.451 dB which is comparable with that designed on standard glass epoxy substrate (?_r = 4.5).     

Enhanced thermal conductivity and dielectric properties of Al/β-SiCw/PVDF composites

Polymeric composites with high thermal conductivity, high dielectric permittivity but low dissipation factor have wide important applications in electronic and electrical industry. In this study, three phases composites consisting of poly(vinylidene fluoride) (PVDF), Al nanoparticles and β-silicon carbide whiskers (β-SiC_w) were prepared. The thermal conductivity, morphological and dielectric properties of the composites were investigated. The results indicate that the addition of 12 vol% β-SiC_w not only improves the thermal conductivity of Al/PVDF from 1.57 to 2.1 W/m K, but also remarkably increases the dielectric constant from 46 to 330 at 100 Hz, whereas the dielectric loss of the composites still remain at relatively low levels similar to that of Al/PVDF at a wider frequency range from 10⁻¹ Hz to 10⁷ Hz. With further increasing the β-SiC_w loading to 20 vol%, the thermal conductivity and dielectric constant of the composites continue to increase, whereas both the dielectric loss and conductivity also rise rapidly.     

Synthesis of ytterbium bisphthalocyanines: Photophysicochemical properties and nonlinear absorption behavior

Herein we report on the syntheses, photophysico-chemical properties and nonlinear absorption parameters of bis-{1(4), 8(11), 15(18), 22(25)-(tetrapyridin-2-yloxy phthalocyaninato)} ytterbium (III) (3) and bis-{1(4), 8(11), 15(18), 22(25)-(tetrapyridin-4-yloxy phthalocyaninato)} ytterbium (III) (4). The fluorescence and singlet oxygen quantum yields obtained for complexes 3 and 4 are low. The triplet quantum yield obtained for complex 3 is high at Φ_T = 0.89 whereas for complex 4 Φ_T = 0.48. The third order optical susceptibility values are of the order: 10⁻¹¹ esu (for complex 3), and 10⁻¹³ esu (for complex 4) while the hyperpolarizability values are of the order: 10⁻²⁸ esu (for complex 3) and 10⁻³¹ esu (for complex 4). Complexes 3 and 4 show two-photon absorption coefficients of the order of 10⁻⁴⁶ cm⁴ s/photon and 10⁻⁴⁸ cm⁴ s/photon, and threshold intensities as low as 0.3 J cm⁻² and 0.0045 J cm⁻², respectively.     

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities

Zeolite-A/chitosan hybrid composites with zeolite contents of 20–55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation–gelation–hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca^2 +-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag⁺-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 μm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca^2 +-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag⁺-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9 × 10⁶ CFU mL^? 1 E. coli concentration to zero within 4 h of incubation time with the Ag⁺-exchanged hybrid composite amount of 0.4 g L^? 1. The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca^2 + and then with Ag⁺. These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.     

Representative indentation elastic modulus evaluated by unloading of nanoindentation made with a point sharp indenter

The conventional method to extract elastic modulus from the nanoindentation on isotropic linearly elastic solids is based on Sneddon’s solution (1965). However, it is known that the solution is valid only for incompressive elastic solids with the Poisson’s ratio ν of 0.5. This paper first proposes the modification of the solution in a wide range of ν from 0 to 0.5 through the numerical analysis on the unloading behavior of a simulated conical nanoindentation with a finite element method. As a result of the modification, the coefficient of linearity between the indentation elastic parameter k_e and Young’s modulus E is empirically given as a function of ν and the inclined face angle of the indenter, β, where k_e is defined as k_e ≡ P/h² with the indentation load P and penetration depth of the indenter h. According to the linear relationship between k_e and E, it is found that elastic rebound during unloading of a nanoindentation is uniquely characterized by a representative indentation elastic modulus E¹ defined in terms of E, ν and β, and that the value of E¹ can be evaluated from the P–h relationship with k_e and β. For an isotropic elastoplastic solid, the indentation unloading parameter k₂ defined as k₂ ≡ P/(h–h_r)² for a residual depth h_r is different from k_e even though a linearly elastic solid with k_e and elastoplastic solid with k₂ have a common E¹. In order to evaluate E¹ of an elastoplastic solid, the corresponding k_e is estimated from k₂ with an empirical equation as a function of the relative residual depth ξ defined as ξ ≡ h_r/h_max for the maximum penetration depth h_max. A nanoindentation experiment confirmed the validity of the numerical analysis for evaluating the elastic modulus.     

(C2N2H10)[FexV1−x(HPO3)F3] (x = 0.44, 0.72): Two new organically templated phosphites: Solvothermal synthesis and structural,thermal, spectroscopic and magnetic studies

(C₂N₂H₁₀)[Fe_xV_1−x(HPO₃)F₃] (x = 0.44, 0.72) have been synthesized using mild solvothermal conditions under autogenous pressure and the ethylenediamine molecule as templating agent. The crystal structures have been determined from X-ray single-crystal diffraction data. The compounds crystallize in the orthorhombic P2₁2₁2₁ space group with Z = 4 and unit-cell parameters a = 12.8494(9), b = 9.5430(6), c = 6.4372(5) Å, and a = 12.8578(1), b = 9.5342(1), c = 6.4370(7) Å for (C₂N₂H₁₀)[Fe_0.44V_0.56(HPO₃)F₃] and (C₂N₂H₁₀)[Fe_0.72V_0.28(HPO₃)F₃], (1) and (2), respectively. These isostructural compounds exhibit a monodimensional crystal structure formed by pillared double anionic chains with the formula [M(HPO₃)F₃]²⁻, extended along the [0 0 1] direction. These doubled ionic chains are the result of the linking of two simple chains in which there are alternating octahedral [MO₃F₃] and tetrahedral groups [HPO₃]. The ethylendiammonium cations are placed in the space delimited by three different chains. The metallic ions are interconnected by the pseudo-pyramidal (HPO₃)²⁻ phosphite oxoanions, adopting a slightly distorted octahedral geometry. The IR spectra show bands corresponding to the phosphite oxoanion and the ethylendiamonium cation at 2400 and 1600 cm⁻¹, respectively. The thermogravimetric analyses show that these phases are stable up to ca. 280 °C, at higher temperatures, the decomposition of the crystal structure begins by calcination of the organic cation and the elimination of the fluoride anions. The diffuse reflectance spectra show bands of the V³⁺ ion (d²) in octahedral symmetry. The values of the Dq (1540, 1540 cm⁻¹), and Racah parameters, B (560, 535 cm⁻¹) and C (3055, 3140 cm⁻¹) for (1) and (2), respectively, correspond with those usually found for octahedrically coordinated V(III) compounds. Magnetic measurements, performed on a powered sample from 5.0 to 300 K at 1000 G, in the ZFC and FC modes, indicate the existence of antiferromagnetic interactions.     

Synthesis and two-photon absorption property of new π-conjugated dendritic fluorophores containing styrylpyridyl moieties

Four new multi-branched two-photon absorption chromophores, namely 1-(4-bromobenzal)-3,5-bis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)benzene (4), tris(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)-benzene (5), 6-chloro-N²,N⁴-bis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)-1,3,5-triazine-2,4-diamine (6), tris-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (7), have been synthesized and characterized. One-photon fluorescence, fluorescent quantum yields and two-photon fluorescence have been investigated. The experimental two-photon absorption cross-sections of 4–7 in DMF are 6, 11, 13 GM (pumped by 740 nm laser) and 19 GM (pumped by 800 nm laser), respectively. The calculated two-photon absorption cross-sections of 4–7 are 5.41, 7.67, 9.57 and 76.14 GM, respectively. The two-photon induced fluorescent peak wavelengths of 4–7 in DMF are 421, 425, 474 and 534 nm pumped by 680, 680, 740 and 800 nm laser, respectively. The results show that molecule 7 is a good two-photon absorption fluorophore possessing long two-photon fluorescent lifetime, good fluorescent quantum yield and large two-photon absorption cross-section. The two-photon absorption peak wavelength of molecule 7 is at 800 nm, which is favourable for initiating two-photon photopolymerization.     

Di- and triorganotin(IV) derivatives of 5-amino-3H-1,3,4-thiadiazole-2-thione as precursors for SnS/SnO2: Thermal studies and related kinetic parameters

Thermogravimetric analysis (TGA) with simultaneous differential thermal analysis (DTA) of R₂SnL₂ (R = methyl (1), n-butyl (2), n-octyl (3) and phenyl (4)) and R₃SnL (R = methyl (5), n-propyl (6), n-butyl (7) and phenyl (8); L = anion of 5-amino-3H-1,3,4-thiadiazole-2-thione) show that in air and nitrogen, diorganotin(IV) thiadiazolates decompose in a different manner, whereas triorganotin(IV) thiadiazolates decompose in a similar way. The decomposition of di- and triorganotin(IV) thiadiazolates occur in two or three steps. The first step of decomposition corresponds to the loss of a ligand/a part of ligand moiety, which is followed by the loss of remaining ligand moiety (in case of diorganotin(IV) thiadiazolates) and the organic groups attached to tin. In case of compounds (3) and (5), tin is partially lost to the gas phase due to sublimation. The residues obtained by thermal decomposition of these compounds are SnS and/or Sn in nitrogen and SnO₂ in air, which are characterized by infrared (IR), far-infrared (far-IR), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Mathematical analysis of thermogravimetric analysis data shows that the first step of decomposition in compounds (4), (6) and (8) in both air and nitrogen follows first order kinetics. Kinetic and thermodynamic data, such as energy of activation (E^*), pre-exponential factor (A), entropy of activation (S^*), free energy of activation (G^*) and enthalpy of activation (H^*) of the first step of decomposition have also been calculated.     

Ferrocene adsorbed into the porous octakis(hydridodimethylsiloxy)silsesquioxane after thermolysis in tetrahydrofuran media: An applied surface for ascorbic acid determination

Octakis(hydridodimethylsiloxi)silsesquioxane (Q₈M₈^H) was synthesized and Ferrocene was adsorbed in a polymeric net through electrostatic interactions, with anion forming after the cleavage of any siloxy groups (ESFc). The nanostructured materials (Q₈M₈^H and EsFc) were characterized by Fourier transform infrared spectra (FT-IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Thermogravimetric analyses and Voltammetric technique The cyclic voltammograms of the graphite paste electrode modified with ESFc showed one redox couple with E⁰′ = 0.320 V (1.0 mol L^?1 NaCl, v = 50 mV s^?1), with a diffusion-controlled process and the redox process shows electrocatalytic activity for the oxidation of ascorbic acid.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Preparation of biomorphic porous calcium titanate and its application for preconcentration of nickel in water and food samples

Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol–gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol–gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4–8, but the adsorbed nickel ion could be completely eluted using 2 mol L^? 1 HNO₃. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g^? 1 and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol^? 1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (E_a) was 25.291 kJ mol^? 1 for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.     

Doping effects of Li–Sb content on the structure and electrical properties of [(Na0.5K0.5)1 − x(Li)x(Sb)x(Nb)1 − xO3] lead-free piezoelectric ceramics

Ceramic samples of [Na_0.5K_0.5]_1 ? x(Li)_x(Sb)_x(Nb)_1 ? xO₃ (NKNLS) (x = 0.04–0.06) were prepared by high temperature solid-state reaction method. X-ray diffraction analysis of the powder samples suggests the formation of a single-phase material with transformation from orthorhombic to tetragonal crystal structure with increase in Sb content. Dielectric studies show a diffuse phase transition about 100 °C and another phase ferroelectric–paraelectric transition at 330 °C. Polarization vs. electric field (P–E) hysteresis studies show maximum remanent polarization (Pr ～ 0.66 C m^?2) for composition x = 0.05. AC conductivity in the compound increases with increase in temperature which may be attributed due to oxygen vacancies and show negative temperature coefficient of resistance (NTCR) effect.     

EPR and optical absorption studies of Cr3+ doped lithium potassium sulphate single crystals

X-band electron paramagnetic resonance (EPR) studies of Cr³⁺ doped lithium potassium sulphate single crystals have been done at room temperature. The Cr³⁺ crystal field and spin Hamiltonian parameters have been evaluated by employing resonance line positions observed in the EPR spectra for different orientations of external magnetic field. The evaluated g, D and E values are: g_x = 2.0763 ± 0.0002, g_y = 1.9878 ± 0.0002, g_z = 1.8685 ± 0.0002 and D = 549 ± 2 × 10^?4 cm^?1, E = 183 ± 2 × 10^?4 cm^?1. Using EPR data the site symmetry of Cr³⁺ ion in the crystal is discussed. Cr³⁺ ion enters the lattice substitutionally replacing K⁺ site. The optical absorption study of the single crystal is also done in 195–925 nm wavelength range at room temperature. By correlating optical and EPR data the nature of bonding in the crystal is discussed. The calculated values of Racah parameters (B and C), crystal field parameter (D_q) and nephelauxetic parameters (h and k) are obtained as: B = 697, C = 3247, D_q = 2050 cm^?1, h = 1.146 and k = 0.21.     

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing Fe2O3—An EPR and optical absorption study

This paper reports the interesting results on mixed alkali effect (MAE) in xLi₂O–(30-x)Na₂O–69.5B₂O₃ (5 ≤ x ≤ 28) glasses containing Fe₂O₃ studied by electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra in these glasses exhibit three resonance signals at g = 7.60, 4.20 and 2.02. The resonance signal at g = 7.60 has been attributed to Fe³⁺ ions in axial symmetry sites whereas the resonance signal at g = 4.20 is due to isolated Fe³⁺ ions in rhombic symmetry site. The resonance signal at g = 2.02 is due to Fe³⁺ ions coupled by exchange interaction. It is interesting to observe that the number of spins participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. The present study also gives an indication that the size of alkali ions we choose in mixed alkali glasses is also an important contributing factor in showing the mixed alkali effect. It is observed that the variation of N with temperature obeys Boltzmann law. A linear relationship is observed between 1/χ and T in accordance with Curie–Weiss law. The paramagnetic Curie temperature (θ_p) is negative for the investigated sample, which suggests that the iron ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. The optical absorption spectra exhibit only one weak band corresponding to the transition ⁶A_1g(S) → ⁴A_1g(G); ⁴E_g(G) at 446 nm which is a characteristic of Fe³⁺ ions in octahedral symmetry.     

Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (k_s), diffusion coefficient (D) and the surface adsorption amount (Γ^?) of ACOP on GR–CS/GCE were determined to be 0.25 s^? 1, 3.61 × 10^? 5 cm² s^? 1 and 1.09 × 10^? 9 mol cm^? 2, respectively. Additionally, a 2e^?/2H⁺ electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0 × 10^? 6 to 1.0 × 10^? 4 M with a low detection limit of 3.0 × 10^? 7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations.     

Acoustic waves in hydrogels: A bi-phasic model for ultrasound tissue-mimicking phantom

In the present paper a continuum poroelastic model for high frequency acoustic waves in hydrogels has been developed. The model has been used to obtain the acoustic longitudinal wave equation for ultrasound.In order to obtain a satisfactory model for hydrogels, a viscoelastic force describing the interaction between the polymer network of the matrix and the bounded water is introduced.The model is validated by means of ultrasound (US) wave speed and attenuation measurements in polyvinylalcohol (PVA) hydrogel samples as a function of their water volume fraction “β” and polymer matrix cross-linking.The model predicts that the law ∝ ν^(1 + δ) for ultrasound attenuation can be applied as a function of the frequency ν, where δ is the frequency exponent of the polymer-bounded water viscosity. This outcome can well explain the attenuation of the US frequency in natural gels where δ is typically about 0.25÷0.50 while the value for pure water is 1.The theory and experiments show that US attenuation in hydrogels decreases steadily with the increase of its water volume fraction β in a linear.The new proposed dissipative mechanism leads to a US wave speed c that follows the law: c = c_w(β ? ?)^? 3/2, where c_w is the US wave speed in water and ? is the volume fraction of the bounded water.Since 0 < β < 1 and ? > 0, the hydrogel US velocity is always higher than that of pure water.If β tends to 1 (100% water), then the US speed in hydrogels converges to a higher value than that of pure water.The US speed gap at β = 1, between hydrogels and water, is the direct consequence of the introduction of the polymer network-bounded water interaction. This is in line with the experimental results that show that the US speed gap at β = 1 decreases in the gel samples with a more cross-linked polymer matrix that has a lower bounded water volume fraction.On the contrary, if the water content is very low (i.e., β < 0.4), the measured US speed converges to that of the dry hydrogel matrix which increases in the samples with a higher degree of network cross-linking with greater elastic moduli.     

Estimation of diffusion parameters in fluidized bed drying

The present work is an attempt to assess the drying kinetics of green pepper in a fluidized bed in a temperature range of 65–105 °C. The drying kinetics is modeled using several semi empirical models to estimate the kinetic parameters. Although the semi empirical model could fit the experimental data well within acceptable experimental error limits, the two parameter models such as Henderson Pabis model and Page Model are identified to predict the drying kinetics with lesser error. The kinetic parameter (k) is found to increase with the temperature for all the models. The activation energy (E) estimated using Arrhenius equation is found to be 30.3 kJ/mol, while the Arrhenius constant (k_o) is found to be 0.09 s^?1. The effective diffusivity coefficient is evaluated using Fick’s diffusion equation which is found increase with increase in temperature of the heating medium and to vary from 1.95 × 10^?11 to 7 × 10^?11 m²/s.