Monitoring the gelation of polyacrylamide–sodium alginate composite by fluorescence technique

Polyacrylamide (PAAm)–sodium alginate (SA) composite was prepared with different amounts of SA varying in the range between 0.06% and 2% (w/v). The PAAm–SA composite was characterized by the steady-state fluorescence technique. Pyranine was added as a fluoroprobe for monitoring the polymerization. It was observed that pyranine molecules bind to AAm and SA chains upon the initiation of the polymerization. Thus, the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol–gel phase transition, and to test the universality of the sol–gel transition as a function of SA contents. Observations around the critical point show that the gel fraction exponent, β, and the weight average degree of polymerization exponent, γ, agreed with the percolation result for (<0.25% (w/v)) SA contents. However, classical results were produced at (<2% (w/v)) SA contents.     

A critical behavior of the Lennard–Jones dimeric fluid in two-dimensions.: A Monte Carlo study

Monte Carlo simulation with hyper-parallel tempering, the histogram reweighting and finite-size scaling techniques are used to explore the critical behavior of Lennard-Jones fluids of dimers in the two-dimensional system. The dimers are built of two distinct segments. The critical parameters for selected types of dimers are estimated. We analyze the influence of the bond length and differences in the chemical nature of segments on the critical parameters. The results can be used to predict the critical parameters of dimers whose molecular parameters are known.     

Facile synthesis of a sulfur/multiwalled carbon nanotube nanocomposite cathode with core–shell structure for lithium rechargeable batteries

A novel sulfur/multiwalled carbon nanotube nanocomposite (S/MWCNT) was prepared by a facile quasi-emulsion template method in an O/W system. Transmission and scanning electronic microscopy show the formation of a highly developed core–shell tubular structure consisting of S/MWCNT composite with uniform sulfur coating on its surface. The homogenous dispersion and integration of MWCNT in the S/MWCNT composite create a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. The S/MWCNT composite cathode could deliver a stable discharge (the fifth cycle) capacity of about 903 mAh g^?1 at 0.1 C, 751 mAh g^?1 at 0.5 C, and 631 mAh g^?1 at 1 C.     

Phase transitions in smectogenic liquid crystal 4-butoxybenzylidene-4′-butylaniline (BBBA) doped by multiwalled carbon nanotubes

The phase transitions in smectogenic liquid crystal BBBA (4-butoxybenzylidene-4′-butylaniline) doped by multi-walled carbon nanotubes (NTs) were studied by methods of optical transmission, differential scanning calorimetry (DSC), measurement of electrical conductivity and analysis of microscopic images. The concentration of NTs was varied within 0–1% wt. Non-monotonous (extremal) changes in temperature, enthalpies and half-width of the DSC peaks of transitions between different phases (smectics, nematic, isotropic) were observed for NT concentrations between 0.05 and 0.1% wt. A noticeable increase of electrical conductivity σ in the same concentration interval evidenced the presence of percolation transition and formation of conductive NT networks. The detailed analysis of σ behavior in the whole concentration interval 0–1% wt revealed the presence of a fuzzy type percolation with multiple thresholds in the studied BBBA?+?NT suspensions. The percolation behavior was strongly dependent on the temperature, and a noticeable step-like drop of σ in the vicinity of isotropic-nematic transition was observed after the multiple heating–cooling cycles.     

A numerical-analytical model for the characterization of composites reinforced by carbon nanotubes

A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.     

Role of Stone–Wales defects on the functionalization of (8,0) single wall carbon nanotubes by the amine group: Ab initio study

Using first-principle calculations, we have investigated the chemical functionalization of (8,0) zigzag single wall carbon nanotubes (SWNTs) by the amine group on Stone–Wales (SW) defects. The binding of NH₂ with the defective (8,0) nanotube was explored and the preferential grafting sites have been identified. On the other hand, the modifications induced by SW defect and functional groups in the structural and electronic properties of (8,0) SWNT have also been investigated. The role of SW defects in the chemical reactivity of carbon nanotubes was well identified.     

Critical behavior in the vicinity of nematic to smectic A (N–SmA) phase transition of two polar–polar binary liquid crystalline systems

Phase diagram, critical behavior and order of the nematic (N)–smectic A (SmA) phase transition of two polar–polar binary systems (i) 4-n-heptyloxy-4′-cyanobiphenyl (7OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB); (ii) 4-n-octyloxy-4′-cyanobiphenyl (8OCB) and 4-n-nonyloxy-4′-cyanobiphenyl (9OCB) by means of a high-resolution temperature scanning measurement of birefringence have been reported in this work. A simple power law analysis has been adopted to extract the specific heat critical exponent (α′) at N–SmA transition from birefringence data. The α′ for N–SmA transition indicates a uniform crossover behavior and has appeared to be non-universal in nature. With increasing concentration of the higher homologues for both the binary systems, the N–SmA transition reveals a strong tendency to be driven towards the tricritical nature. The 3D-XY limit (i.e. α′ = ?0.007) for N–SmA transition reaches at the concentration x_8OCB = 0.28 corresponding to the McMillan ratio 0.914, whereas the tricritical point has been found to appear near x_9OCB = 1.0 corresponding to McMillan ratio 0.992.     

A study on fluorescence quenching of LD-425 by aromatic amines in 1,4-dioxane–acetonitrile mixtures

The fluorescence quenching of 4-methyl-7-(4-morpholiny)-2H-pyrano[2,3-b]pyridin-2-one (LD-425) by aromatic amines aniline (AN), dimethyl aniline (DMAN) and diethyl aniline (DEAN) in solvent mixtures of 1,4-dioxane and acetonitrile has been studied at room temperature by steady-state and time-resolved methods. The positive deviation from linearity has been observed in the Stern–Volmer (S–V) plots. Various quenching rate parameters have been determined using the extended S–V equation and are found to be dependent on solvent polarity. The quenching ability of amines increases with increase in their ionization energies. Further, with the use of the sphere of action static quenching model and finite sink approximation model, it is concluded that the bimolecular quenching reactions are due to the presence of both dynamic and static quenching processes.     

Hydrogen implantation in Ni(111) — A study of H2 desorption dynamics from the bulk

Hydrogen implanted in Ni(111) has been investigated by the use of temperature programmed desorption (TPD) as a function of implantation energy (0.08–5.0 keV) and dose (0−2.6 × 10¹⁷ H⁺₂cm⁻²). The amount of hydrogen implanted was calibrated by comparison to the amount chemisorbed on the surface since separation of the desorption features for the two types of hydrogen was possible. It is shown that trap formation plays an important role in the observed behavior of the implanted hydrogen desorption features for implantation energies above 1.0 keV. The desorption of implanted hydrogen is found to be strongly forward-peaked along the crystal surface normal. Since the surface was saturated with hydrogen when the implanted hydrogen was released, this effect is explained by recombination of an implanted and a chemisorbed hydrogen atom. Here, a translationally excited H₂ molecule desorbing from the surface is produced by a hydrogen atom originating from an elevated potential region inside the solid.     

A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX(China Dark matter EXperiment)Collaboration will carry out a direct search for WIMPs(Weakly Interacting Massive Particles)using an Ultra-Low Energy Threshold High Purity Germanium(ULE-HPGe)detector at the CJPL(China JinPing deep underground Laboratory).A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of T rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction.Furthermore,the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal.Compared with the radiopurity reported by other low-background rare-event experiments,it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX (China Dark matter EXperiment) Collaboration will carry out a direct search for WIMPs (Weakly Interacting Massive Particles) using an Ultra-Low Energy Threshold High Purity Germanium (ULE-HPGe) detector at the CJPL (China JinPing deep underground Laboratory). A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of γ rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction. Furthermore, the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal. Compared with the radiopurity reported by other low-background rare-event experiments, it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

First principles study of behavior of helium at Fe(110)–graphene interface

Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless steels with Fe as main matrix are widely used in nuclear systems.Therefore,in this study,the atomic behaviors of point defects and helium(He) atoms at the Fe(110)-graphene interface are investigated systematically by first principles calculations.The results indicate that graphene interacts strongly with the Fe(110) substrate.In comparison with those of the original graphene and bulk Fe,the formation energy values of C vacancies and Fe point defects decrease significantly for Fe(110)-graphene.However,as He atoms have a high migration barrier and large binding energy at the interface,they are trapped at the interface once they enter into it.These theoretical results suggest that the Fe(110)-graphene interface acts as a strong sink that traps defects,suggesting the potential usage of steel-graphene with multiply interface structures for tolerating the radiation damage.     

Reprint of : Kondo effect in a carbon nanotube with spin–orbit interaction and valley mixing: A DM-NRG study

We investigate the effects of spin–orbit interaction (SOI) and valley mixing on the transport and dynamical properties of a carbon nanotube (CNT) quantum dot in the Kondo regime. As these perturbations break the pseudo-spin symmetry in the CNT spectrum but preserve time-reversal symmetry, they induce a finite splitting $\Delta$ between formerly degenerate Kramers pairs. Correspondingly, a crossover from the SU(4) to the SU(2)-Kondo effect occurs as the strength of these symmetry breaking parameters is varied. Clear signatures of the crossover are discussed both at the level of the spectral function as well as of the conductance. In particular, we demonstrate numerically and support with scaling arguments that the Kondo temperature scales inversely with the splitting $\Delta$ in the crossover regime. In presence of a finite magnetic field, time reversal symmetry is also broken. We investigate the effects of both parallel and perpendicular fields (with respect to the tube's axis) and discuss the conditions under which Kondo revivals may be achieved.     

A comparison of the magnetic and microwave absorption properties of Mn–Sn–Ti substituted strontium ferrite with and without multi-walled carbon nanotube

In this work, a comparison of magnetic and microwave properties between Mn–Sn–Ti substituted SrM ferrite and nanocomposite of Mn–Sn–Ti substituted SrM ferrite–20% volume multi-walled carbon nanotube (MWCNT) has been done. Phase characterization and crystal structure of the synthesized nanoparticles were tested by X-ray diffraction (XRD). Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrometry (FTIR) analysis approved that the SrFe_12−x(MnSn_0.5Ti_0.5)_x/2O₁₉ nanoparticles were attached on the external surfaces of the MWCNTs. Mӧssbauer spectroscopy (M_S) showed the occupancy by non-magnetic Mn²⁺–Sn⁴⁺–Ti⁴⁺ cations into the hexagonal lattice structure. Magnetic properties were evaluated by a vibrating sample magnetometer (VSM). The results also indicated that saturation magnetization and coercivity were decreased with an increase in x content and also MWCNTs addition. Microwave absorption properties were investigated by a vector network analyzer (VNA). It was found that with an addition of 20 volume percentage of MWCNTs, the saturation magnetization coupled with coercivity decrease, but reflection loss (RL) increase broadly. Also it proved that with an increase in the thickness of absorption the frequency band shifts from K_u (12–18 GHz) to X (8–12 GHz) band.     

Anchoring of triethanolamine–Cu(II) complex on magnetic carbon nanotube as a promising recyclable catalyst for the synthesis of 5-substituted 1H-tetrazoles from aldehydes

Molecular Diversity - The development of heterogenization of copper nanoparticles on conductive supports is very challenging and has received much attention. Here, we synthesize a practical,...     

Surface modification of bulk n-InAs (111)A etched in bromine–methanol

X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman and photoluminescence spectroscopy were used to evaluate the surface properties of n-type InAs (111)A etched in a 1% Br–methanol solution. Etching completely removes the native oxides from the surface and enhances the photoluminescence response. The adsorption of bromine onto the InAs surface leads to the formation of In–Br_x and As–Br_x bonds (x = 1, 2, 3) as inferred from changes in the In 3d_3/2;5/2 and As 3d core level binding energies. The etch rate is found to decrease due to strong anisotropic effects and the high volatility of the bromine species. A 1 min Br–methanol etch was found to enhance the photoluminescence intensity by a factor of 3, probably due to a reduction in the surface state density upon de-oxidation of the surface. This is thought to be due to reductions in the surface state density. The presence of native oxides enhances both the surface accumulation layer and the surface state density.     

Manganese(III)-promoted reactions for formation of carbon–heteroatom bonds

Manganese(III) reagent is an important one- electron oxidant for initiation of free-radical reactions and formation of carbon–carbon bonds. The reactions are usually carried out under mild conditions, have high regio- and stereo-selectivities, and good functional group tolerance. Summarized in this article are the developments of manganese (III)-based reactions for the formation of carbon–heteroatom bonds including carbon–oxygen, carbon–phosphorus, carbon–sulfur, and carbon–nitrogen bonds, and their applications for the synthesis of related heterocyclic systems.     

Thermoluminescence (TL) of europium-doped ZrO2 obtained by sol–gel method

This article reports the preparation and characterization of europium-doped zirconium oxide (ZrO₂:Eu³⁺) formed by homogeneous precipitation from propoxyde of zirconium [Zr(OC₃H₇)₄]. The alkoxide sol gel process is an efficient method to prepare the zirconium oxide matrix by the hydrolysis of alkoxide precursors followed by condensation to yield a polymeric oxo-bridged ZrO₂ network. All compounds were characterized by thermal analysis and the X-ray diffractometry method. The thermoluminescence (TL) emission properties of ZrO₂:Eu³⁺ under beta radiation effects are studied. The europium-doped sintered zirconia powder presents a TL glow curve with two peaks (Tmax) centered at around 204 and around 292 ^°C, respectively. TL response of ZrO₂:Eu³⁺ as a function of beta-absorbed dose was linear from 2 Gy up to 90 Gy. The europium ion (Eu³⁺)-doped ZrO₂ was found to be more sensitive to beta radiation than undoped ZrO₂ obtained by the same method and presented a little fading of the TL signal compared with undoped zirconium oxide.