Solution Research Articles

Intrinsic and extrinsic contributions in the ferroelectric response of chemically synthesized BiFeO3-xPbTiO3 thin films

Multiferroic (BiFeO3)1−x-(PbTiO3)x (1−x)BF−xPT thin films exhibit very high electromechanical properties in the vicinity of the morphotropic phase boundary (MPB), making them important candidates for use in several modern device applications. However, preparing high-quality (1−x)BF−xPT thin films is challenging due to the high conductivity caused by oxygen vacancies produced during the synthesis process. This study aims to understand the effect of size and porosity density on the electrical properties of (1−x)BF−xPT thin films. A series of (1−x)BF−xPT solid solution thin films were fabricated using the spin-coating method on Pt/TiO2/SiO2/Si(100) substrates through chemical solution deposition. X-ray diffraction studies revealed a polycrystalline structure. Surface SEM images showed that the films have a uniform surface with average grain sizes ranging between 50 and 200 nm and an average film thickness of 1.5 μm. A decrease in average pore size and an increase in the number of pores were observed with the increase in PT concentration in the prepared films. Ferroelectric characterization revealed that the films exhibit room-temperature ferroelectric hysteresis loops. Sources of various contributions to polarization were extracted from hysteresis loops, including true ferroelectric switching and space charge contributions. Thin films with 0.30 < x < 0.45 show higher remanent and saturation polarization values, suggesting that these compositions exhibit the MPB. The highest remanent polarization value (PR = 16.68 μC/cm2) was observed for the thin film with x = 0.40. The correlation between the phase, composition, film morphology, and ferroelectric response is described and discussed.

Efficient separation of radium from natural thorium using a mesoporous silica-supported composite resin with sulfonic acid groups for the acquisition of targeted α-nuclides 212Pb

212Pb serves as one of the most important nuclides for targeted alpha therapy (TAT), with good potential in the treatment of malignant tumors. However, medical and clinical applications are seriously limited by its extremely short supply, which strongly depends on the acquisition of its parent nuclides such as 228Ra or 224Ra. To address this issue, we conducted a systematic investigation on the separation of trace radium from natural thorium using the ion exchange chromatography method, and a novel porous silica-based composite resin functionalized with sulfonic acid groups was prepared, characterized, and employed. Experimental results showed that the silica-supported resin was successfully prepared with the sulfonic acid groups, and possessed small particle size, mesoporous pore structure and large specific surface area. The resin exhibited high selectivity toward thorium compared with barium, and the separation factor reached 123 at low acidity and at low temperature. The resin demonstrated a fast adsorption speed and an excellent separation performance, and the adsorption mechanism was confirmed based on the ion exchange between the sodium carried and the target cations. On the basis, column experiments were further conducted and finally the separation of trace radium from thorium was realized using a small column filled with about 1.0 g resin. The chemical recovery of radium reached 97 %, and the decontamination factor for thorium exceeded 40,000. This work verifies the feasibility of directly extracting 228Ra and 224Ra from natural thorium using the sulfonic acid group functionalized materials in the dilute nitric acid solution, and presents an excellent material and systematic experimental data on the separation activities, rendering this study particularly significant.

Synthesis and characterization of polylactic acid‐lecithin‐starch bioplastic film

AbstractPlastic‐induced environmental issues could be solved using biomaterials, such as polylactic acid (PLA) film. PLA film is a costly solution suggesting the need to add less expensive starch. However, PLA and starch do not mix due to their diverging water behavior. In this study, we evaluated the impact of lecithin as a compatibilizer in varying ratio of PLA and starch film. The results show that inclusion of lecithin in PLA/starch composite leads to enhanced mechanical properties compared with the composite without lecithin. All films' thermal properties were stable but the thermograph of PLA/starch display two peaks whose distance is impacted by lecithin. In addition, morphology and functional group fingerprints revealed that the addition of lecithin improved the interfacial adhesion between the two polymers. Lecithin influenced the positioning and dispersion pattern of starch granules and distinct transmittance characteristics. The improved compatibility of PLA/starch makes the resulting films less susceptible to water penetration and dissolution. This work demonstrated the possibility of using lecithin as emulsifier between PLA and starch which could expand the application of PLA/starch film especially in packaging industries and bale net wrapping.

Experimental and computational characterization of p-Sulfocalix[4]arene mediated delivery system for morin hydrate

Calix[n]arene is a class of macrocyclic compounds and has been investigated to improve the physicochemical properties of water insoluble molecules. In this work, a complex of morin hydrate (MH) drug was prepared using p-sulfocalix[4]arene (SC[4]A) as complexing agent to increase its water solubility, dissolution rate and stability. Solvent evaporation methanol was used to prepare the inclusion complex (MH-SC[4]A) between pure MH and SC[4]A and analysed by FTIR, NMR, UV, DLS, TEM, and DSC techniques. Concentration-dependent solubility study showed 22 folds enhancement of MH at 8 mM concentration of SC[4]A. The in vitro anticancer efficacy of MH against A549 cells was increased after complex formation. AO/EtBr staining study showed the more apoptosis mediated anticancer activity than native MH. Molecular geometry, stabilizing interactions, release behaviour and full-unwinding pathway of the complex were characterized by the computed Potential of Mean Force (PMF) using extended umbrella sampling. The combined computational and experimental data confirmed that our designed MH-SC[4]A complex could be utilized as a promising drug delivery carrier for hydrophobic MH.

Multistability of elasto-inertial two-dimensional channel flow

Elasto-inertial turbulence (EIT) is a recently discovered two-dimensional chaotic flow state observed in dilute polymer solutions. Two possibilities are currently hypothesized to be linked to the dynamical origins of EIT: (i) viscoelastic Tollmien–Schlichting waves and (ii) a centre-mode instability. The nonlinear evolution of the centre mode leads to a travelling wave with an ‘arrowhead’ structure in the polymer conformation, a structure also observed instantaneously in simulations of EIT. In this work we conduct a suite of two-dimensional direct numerical simulations spanning a wide range of polymeric flow parameters to examine the possible dynamical connection between the arrowhead and EIT. Our calculations reveal (up to) four coexistent attractors: the laminar state and a steady arrowhead regime (SAR), along with EIT and a ‘chaotic arrowhead regime’ (CAR). The SAR is stable for all parameters considered here, while the final pair of (chaotic) flow states are visually very similar and can be distinguished only by the presence of a weak polymer arrowhead structure in the CAR regime. Analysis of energy transfers between the flow and the polymer indicates that both chaotic regimes are maintained by an identical near-wall mechanism and that the weak arrowhead does not play a role. Our results suggest that the arrowhead is a benign flow structure that is disconnected from the self-sustaining mechanics of EIT.

Comparison of Polypentenamer and Polynorbornene Bottlebrushes in Dilute Solution.

Bottlebrush (BB) polymers were synthesized via grafting-from-atom transfer radical polymerization (ATRP) of styrene on polypentenamer and polynorbornene macroinitiators with matched grafting density (n g = 4) and backbone degrees of polymerization (122 ≥ N bb ≥ 61) to produce a comparative study on their respective dilute solution properties as a function of increasing side chain degree of polymerization (116 ≥ N sc ≥ 5). The grafting-from technique produced near quantitative grafting efficiency and narrow dispersity N sc as evidenced by spectroscopic analysis and ring closing metathesis depolymerization of the polypentenamer BBs. The versatility of this synthetic approach permitted a comprehensive survey of power law expressions that arise from monitoring intrinsic viscosity, hydrodynamic radius, and radius of gyration as a function of increasing the molar mass of the BBs by increasing N sc. These values were compared to a series of linear (nongrafted, N sc = 0) macroinitiators in addition to linear grafts. This unique study allowed elucidation of the onset of bottlebrush behavior for two different types of bottlebrush backbones with identical grafting density but inherently different flexibility. In addition, grafting-from ATRP of methyl acrylate on a polypentenamer macroinitiator allowed the observation of the effects of graft chemistry in comparison to polystyrene. Differences in the observed scaling relationships in dilute solution as a function of each of these synthetic variants are discussed.

The effect of thiol ligands on the adsorption behavior of silver ions on functionalized nanomagnetic graphene oxides

The magnetic graphene oxides (MGO) were modified with l-cysteine (Cys), glutathione (GSH), and thioglycolic acid (TGA) as the thiol ligands. using field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and Brunauer Emmett Teller (BET) surface area analysis, the structural and magnetic properties of the as-prepared samples have been studied. The results affirmed the successful synthesis of functionalized adsorbents. The adsorbents presented here have been reported for the first time to remove Ag ions from dilute aqueous solutions. The influence of the adsorption conditions (pH, contact time, and initial concentration) was investigated. The experimental data were consistent with both the pseudo-second-order kinetic model and the Langmuir isotherm model indicating chemisorption monolayer adsorption with the fast kinetics. The maximum adsorption capacity for MGO-TGA, MGO-Cys, and MGO-GSH based on the Langmuir isotherm model was found to be qm = 67.16, 53.42, and 43.73 mg/g, respectively. The calculated separation factors (0 < RL < 1) revealed that the adsorption process was favorable for three adsorbents. The large surface area of the adsorbents (57.244, 37.006, and 15.676 m2/g, for MGO-TGA, MGO-Cys, and MGO-GSH, respectively), along with the presence of thiol ligands on them, significantly affects the adsorption behavior. Therefore, these adsorbents offer an effective and rapid process for adsorbing silver ions from low concentration aqueous solutions.

Development of a novel fluorimetric sensor based on polypyrrole doped with 4-(methylsulfonyl)-2-nitrobenzoic acid (MSNBA) for sensitive detection of copper (Cu2+)

In this study, we successfully electrochemically synthesized a polypyrrole film doped with 4-methylsulfonyl-2-nitrobenzoic acid (MSNBA) within an aqueous medium containing 0.01 M MSNBA, 0.003 M NaOH, and 0.01 M pyrrole. Our investigation encompassed a thorough exploration of both electrochemical and spectroscopic properties, confirming the effective incorporation of MSNBA as a dopant within the electroactive PPy chain. The morphological characterization of the film was undertaken using scanning electron microscopy (SEM). The optical properties, particularly UV–visible absorption, and fluorescence spectroscopy, were scrutinized in a dilute DMF solution. The UV–visible absorption spectra revealed a broad absorption band centered around 292 nm, attributed to the π→π* 1B - 1La/1Lb transitions of the oligo-benzenes in the film. In parallel, fluorescence spectra exhibited remarkable consistency between the solid state and solution, featuring an excitation peak at 345 nm (346 nm in solution) and an emission peak around 401 nm (403 nm in solution). Exploring the impact of copper (II) ions on absorption and fluorescence spectra unveiled a notable quenching effect along two distinct linearity domains. Various mathematical treatments, including the Stern-Volmer equation (R1 = 0.98, Ksv1 = 5.104 and R2 = 0.99, Ksv2 = 1.54.106), the Perrin equation, and the polynomial equation, were applied to elucidate the nature of this fluorescence quenching. Our findings indicated that the fluorescence extinction, as a function of Cu2+ ion concentration, aligns well with the polynomial equation, signifying a combination of dynamic and static quenching (Io/I = 1.08(±0.04) + 1.46(±0.44)105[Q]- 1.15(±0.75)1010 [Q]2). Moreover, we explored the potential application of this method for the determination of Cu2+. Calibration graphs demonstrated excellent linearity between fluorescence intensity and Cu2+ concentration in the range of 0–5.4 μM. Notably, the detection limit of 1.2 μM surpassed the LOD for Cu2+ (20 μM) in drinking water set by the EPA, suggesting the viability of this approach for sensitive detection in environmental monitoring.

Optical, conductive, and ferroelectric properties of the first layer of dip-coated BiFeO3 films from methoxyethanol and acetic acid-based chemical dissolvents

The overall performance of the multilayer resulting in a sol-gel bismuth ferrite (BiFeO3) film will be primarily determined by the properties of the first layer, but this has yet to receive much attention, even though chemical and morphological defects of this layer can accumulate as the number of layers increases. Here, we perform an optical, conductive, and ferroelectric study of first layer (L 1) dip-coating sol-gel BiFeO3 films using two routes that vary only in the dissolvent; the first one is based on 2-methoxyethanol (MOE), and the second one on acetic acid (AA) with some MOE (AA-MOE). Tauc plots reveal a band gap of 2.43 eV and 2.75 eV for MOE (30 ± 5 nm thick) and AA-MOE (35 ± 5 nm thick) films, respectively. MOE films showed a dielectric function with features at ∼2.5 eV, ∼3.1 eV, and ∼3.9 eV, which were associated with charge-transfer transitions, but such features are absent in AA-MOE films. Advanced atomic force microscopy techniques were used to identify the fine features or defects of the BiFeO3 films: The conductive maps show that the charge transport pathways in both film routes are controlled by nanometer defects rather than grain or grain boundary defects. Current-voltage curves reveal high conductive pathway at a lower voltage for the MOE films than for AA-MOE films. The piezoelectric coefficient for MOE films was ∼20% higher than AA-MOE films. Both deposition methods yield ferroelectric films with an electromechanical strain controlled by the piezoelectric effect and minimal contribution from electrostriction. An optimization for the AA-MOE-based route in the withdrawal speed results in a significant reduction of morphological defects and a more than twofold increase in the piezoelectric coefficient. Our results broaden the understanding of optical and ferroelectric BiFeO3 films based on a chemical solution by dip-coating.

AIE Luminogen-Rhodamine 6G FRET pair based light harvester and Hg2+ chemosensor for real life applications

Aggregation Induced Emission (AIE) is an intriguing photophysical phenomenon exhibited by certain chromophores that are non-emissive in dilute solutions but are induced to emit light upon aggregation. A “Turn-on” emission has been observed in Dodecyl Carbazole-Barbituric acid conjugate (DCBA) with the addition of poor solvent like water. FRET between an AIE luminogen- DCBA as donor and Rh6G as acceptor has been investigated using steady-state and time-resolved fluorescence studies. There is a significant spectral overlap between the AIE emission of DCBA and the absorption spectra of Rh6G in 9:1 water to THF binary solution. DCBA AIE emission quenching upon addition of Rh6G is identified as due to FRET. The energy transfer efficiency is found to increase linearly with acceptor concentration, reaching an optimum efficiency of 43 %. It holds the promise of being a multiple-donor single-acceptor artificial light harvesting antenna, with an antenna effect of 20.5 %. The proposed FRET system demonstrates excellent pH stability in pH range of 3 to 11. This FRET pair can serve as a turn off fluorescent probe in real water samples and live cells for sensing of Hg2+ ions with high sensitivity, selectivity, and low cytotoxicity. The sensor is also effective for paper strip based Hg2+ detection.

Gold Nanoparticle-Modified Carbon-Fiber Microelectrodes for the Electrochemical Detection of Cd2+ via Fast-Scan Cyclic Voltammetry.

Neurotoxic heavy metals, such as Cd2+, pose a significant global health concern due to their increased environmental contamination and subsequent detrimental health hazards they pose to human beings. These metal ions can breach the blood-brain barrierblood-brain barrier, leading to severe and often irreversible damage to the central nervous system and other vital organs. Therefore, developing a highly sensitive, robust, and rapid in vivo detection method for these hazardous heavy metal ions is of the utmost importance for early detection, thus initiating timely therapeutics. Detecting ultra-low levels of toxic metal ions in vivo and obtaining accurate speciation information remains a challenge with conventional analytical techniques. In this study, we fabricated a novel carbon carbon-fiber microelectrode (CFM)-based sensor that can detect Cd2+ ions using fast-scan cyclic voltammetry by electrodepositing gold nanoparticles (AuNP). We optimized electrochemical parameters that generate a unique cyclic voltammogram (CV) of Cd2+ at a temporal resolution of 100 ms with our novel sensor. All our experiments were performed in tris buffer that mimics the artificial cerebellum fluid. We established a calibration curve resulting in a limit of detection (LOD) of 0.01 µM with a corresponding sensitivity of 418.02 nA/ µM. The sensor's selectivity was evaluated in the presence of other metal ions, and it was noteworthy to observe that the sensor retained its ability to produce the distinctive Cd2+ CV, even when the concentration of other metal ions was 200 times higher than that of Cd2+. We also found that our sensor could detect free Cd2+ ions in the presence of complexing agents. Furthermore, we analyzed the solution chemistry of each of those Cd2+-ligand solutions using a geochemical model, PHREEQC. The concentrations of free Cd2+ ions determined through our electrochemical data align well with geochemical modeling data, thus validating the response of our novel sensor. Furthermore, we reassessed our sensor's LOD in tris buffer based on the concentration of free Cd2+ ions determined through PHREEQC analysis, revealing an LOD of 0.00132 µM. We also demonstrated the capability of our sensor to detect Cd2+ ions in artificial urine samples, showcasing its potential for application in actual biological samples. To the best of our knowledge, this is the first AuNP-modified, CFM-based Cd2+ sensor capable of detecting ultra-low concentrations of free Cd2+ ions in different complex matrices, including artificial urine at a temporal resolution of 100 ms, making it an excellent analytical tool for future real-time, in vivo detection, particularly in the brain.

Purely elastic turbulence in pressure-driven channel flows

Solutions of long, flexible polymer molecules are complex fluids that simultaneously exhibit fluid-like and solid-like behavior. When subjected to an external flow, dilute polymer solutions exhibit elastic turbulence-a unique, chaotic flow state absent in Newtonian fluids, like water. Unlike its Newtonian counterpart, elastic turbulence is caused by polymer molecules stretching and aligning in the flow, and can occur at vanishing inertia. While experimental realizations of elastic turbulence are well-documented, there is currently no understanding of its mechanism. Here, we present large-scale direct numerical simulations of elastic turbulence in pressure-driven flows through straight channels. We demonstrate that the transition to elastic turbulence is sub-critical, giving rise to spot-like flow structures that, further away from the transition, eventually spread throughout the domain. We provide evidence that elastic turbulence is organized around unstable coherent states that are localized close to the channel midplane.

Effect of End Groups on the Cloud Point Temperature of Aqueous Solutions of Thermoresponsive Polymers: An Inside View by Flory-Huggins Theory.

In an effort to gain insight into the origin of the effects of end groups on the cloud point temperature (Tcp) as a function of the polymer molar mass of thermoresponsive polymers with lower critical solution behavior in dilute aqueous solutions, we use the Flory-Huggins (FH) theory amended for end groups. The theory was applied to available experimental data sets of poly(N-isopropylacrylamide) (PNIPAM), poly(4-vinylbenzyl methoxytris(oxyethylene) ether) (PTEGSt), and poly(α-hydro-ω-(4-vinylbenzyl)tetrakis(oxyethylene) ether) (PHTrEGSt). The theory relates the variations in TcpM,ϕcp for different end groups to the effective FH χ parameter of the end groups and explains the qualitative notion that the influence of the end groups is related to the hydrophobicity/hydrophilicity of the end groups relative to that of the so called intrinsic TcpM,ϕcp response of a polymer without end groups. The limits to the applicability of the FH theory are established, and a set of possible theoretical improvements is considered. The ultimate scrutiny of the simple FH theory and suggested improved theories must await the measurement of truly thermodynamic cloud points; the available cloud points are merely estimations of the thermodynamic cloud point, for which the deviation to the true cloud point cannot be established with sufficient accuracy.

PH-Modulated 1D Hierarchical Self-Assembly of a Brush-Like Poly-Para-Phenylene Homopolymer.

The controllable self-assembly of conjugated homopolymers, especially homopolymers without other segments (a prerequisite for phase separation), which can afford chances to achieve tunable optical/electronic properties, remains a great challenge due to their poor solubility and has remained rarely documented. Herein, a conjugated homopolymer (DPPP-COOH) is synthesized, which has a unique brush-like structure with a conjugated dendritic poly-para-phenylene (DPPP) backbone and alkyl-carboxyl side chains at both edges of the backbone. The introduction of carboxyl makes the brush-like homopolymer exhibit pH-modulated 1D hierarchical self-assembly behavior in dilute solution, and allows for flexible morphological regulation of the assemblies, forming some uncommon superstructures including ultralong nanowires (at pH 7), superhelices (at pH 10) and "single-wall" nanotubes (at pH 13), respectively. Furthermore, the good aqueous dispersibility and 1D feature endow the superstructures formed in a high-concentration neutral solution with high broad-spectrum antibacterial performance superior to that of many conventional 1D materials.

Polymerization of benzoxazine impregnated in porous carbons. A scalable and low-cost route to smart copper-ion absorbents with saturation indicator function

Porous carbon materials are common materials used for sensor and absorbent applications. A novel approach for functionalizing porous carbons through the impregnation of porous carbon black with benzoxazine monomers, followed by thermal polymerization is introduced herein. The method not only establishes a new avenue for the functionalization of porous carbons but also endows the resulting material with both copper ion-binding and sensing properties. We showcase the versatility of the technique by illustrating that the polymerization of phenols with benzoxazine monomers serves as an extra tool to customize absorption- and sensing properties. Experimental validation involved testing the method on carbon black as a porous substrate, which was impregnated with both bisphenol-a benzoxazine and a combination of bisphenol-a benzoxazine and alizarin. The resulting materials were assessed for their dual functionality as both an absorbent and a sensor for copper ions by varied copper ion concentrations and exposure times. The dye absorption test demonstrated a notable capacity to accumulate copper ions from dilute solutions. Electrochemical characterization further confirmed the effectiveness of the modified carbons, as electrodes produced from inks were successful in detecting copper ions accumulated from 50 μM Cu2+ solutions. With this work, we aspire to set the steppingstone towards a facile functionalization of porous carbon materials towards water purification applications.

Significant enhancement of Jc of MgB2 by doping organic carbon with chemical solution methods

MgB2 superconductors have the potential for application at 20 K, and improving their superconducting current carrying capacity is the key to achieving this application. In this article, the doping effects of organic carbon (citric acid, C6H8O7) on the critical temperature (Tc), critical current density (Jc), and irreversible field (Hirr) of MgB2 was studied, in order to explore the path of improving its superconducting performance at 20 K. Combing hot-pressing sintering and chemical solution route for making the samples, it was observed that a moderate level of doping (10 wt%) significantly improved the Jc of MgB2 at 20 K: the 2 T-infield Jc of 10 wt% doped sample reaches a value of 30400 A/cm2, increased by 56.7% compared to the undoped sample. The mechanism beneath the improved performance is studied and attributed to the rapidly enhanced δl-type flux pinning force brought about by partial substitution of C for B. In addition, the grain refinement effect caused by C doping strengthens the surface pinning force, resulting in a better agreement between the scaling behavior of the pinning force density and the theoretical model of surface pinning.

Effect of solution chemistry on the sedimentation, dissolution, and aggregation of the bimetallic Fe/Cu nanoparticles pre- and post-grafted with carboxymethyl cellulose

The suitability of iron-based nanomaterials or composites for in-situ remediation hinges on their physicochemical stability. Introducing surface modifications like metal doping or polymer grafting can regulate interparticle forces, influencing particle stability. Thus, probing how grafting methods (i.e., pre- or post-grafting) tune material properties controlling interparticle forces, comprehend the synergistic effect of metal doping and polymer grafting, and evaluate stability under varying geochemical conditions are the way forward in designing sustainable remediation strategies. To this end, time-dependent sedimentation, dissolution, and aggregation of four synthesized iron-based nanoparticles (bare iron (Fe), copper doped bimetallic iron/copper (Fe/Cu), pre- and post-grafted Fe/Cu with carboxymethyl cellulose (CMC) – CMCpre-Fe/Cu and CMCpost-Fe/Cu, respectively) were carried out as a function of solution chemistry (i.e., pH – 5 to 10, ionic strength, IS – 0 to 100 mM NaCl, initial particle concentration, C0–20 to 200 mg.L−1) mimicking geoenvironmental conditions. CMCpre-Fe/Cu exhibited markedly higher particle availability (> 91 %) against sedimentation than others (bare Fe/Cu (11.28 %) > bare Fe (7.33 %) > CMCpost-Fe/Cu (6.09 %)) – suggesting the pivotal role of grafting method on particle stability. XDLVO energy profiles revealed pre-grafting altered magnetic properties favoring surface charge-driven electrostatic repulsion over magnetic attraction, thereby limiting aggregation-induced particle settling. In contrast, superior magnetic force overrides the electrostatic behavior for bare and post-grafted particles. Unlike bare and post-grafted nanoparticles, CMCpre-Fe/Cu aggregate size correlated positively with [H+] and IS, consistent with their settling behavior. Rise in C0 showed a visible negative effect on particle aggregation and, thereby, sedimentation except for CMCpre-Fe/Cu by facilitating particle collision through Brownian movement. Both acidic pH and copper doping promoted nanoparticle dissolution, whereas pre-grafting can provide a plausible solution against nanoparticle toxicity and loss of reactivity due to ionic release. To recapitulate, these findings are imperative in building a sustainable framework for environmental remediation application.

Crystallinity improvements in cellulose II after multiple posttreatment cycles with a dilute NaOH solution

Crystallinity improvements in cellulose II after multiple posttreatment cycles with a dilute NaOH solution

Solute Effects on Growth Restriction in Dilute Ferrous Alloys

The effect of dilute solute additions on growth restriction in binary ferrous alloys has been assessed by means of the heuristic growth restriction parameter (β) modelling framework (Fan et al. in Acta Mater. 152, 248–257, 2018). The CALPHAD (CALculation of PHAse Diagrams) methodology (Kaufman and Bernstein in Computer Calculation of Phase Diagrams, 1970) has been used to calculate β values from the liquidus slope m and the equilibrium distribution coefficient k values, at first approximation, in conjunction with the liquid-to-solid fraction to obtain true β values. Critical solute concentrations, below which solidification becomes partitionless, have also been calculated. Among 23 dilute binary ferrous alloy systems investigated, the five most efficient solutes on grain refinement are B, Y, O, S and C. A negative correlation, or inverse relationship, was observed between the true β values and the grain size values obtained from a study on experimental multicomponent dilute ferrous alloy systems (Li et al. in Metall. Mater. Trans. A 49 A, 2235–2247, 2018).

Significant enhancement of Jc and flux pinning mechanism of MgB2 doped with PEG-polymers

Compared with traditional low-temperature superconductors, the advantage of MgB2 lies in its critical temperature close to 40 K, which provides potential application at 20 K. In order to further improve its superconducting current carrying capacity at 20 K, a series of PEG polymer (including PEG2000, PEG4000, and PEG6000) doped MgB2 with doping level of 15 wt% were prepared by combining hot-pressing sintering with chemical solution route. The best result is achieved in PEG4000 doped sample, with a Jc at 20 K and 2 T reaching 51,000 A/cm2, increased by 42.8 % in comparison with the undoped sample. Study on the mechanism of the improvement reveals that organic carbon doping enhances the irreversibility field and consequently the flux pinning force. In response to the deviation of MgB2 pinning characteristics from Kramer theory, an irreversibility field increment (IFI) model was proposed which provides a satisfactory explanation for the experimental results. Our results demonstrate that the combination of hot-pressing sintering and organic carbon doping is an effective means to enhance the superconducting performance of MgB2 at 20 K for practical applications.