Mechanism Of Property Enhancement Research Articles

Investigations of Morphology and Carrier Transport Characteristics in High‐Performance PEDOT:PSS/Tellurium Binary Composite Fibers Produced via Continuous Wet‐Spinning

AbstractFiber‐based flexible thermoelectric (TE) generators are highly desirable due to their capability to convert thermal energy into electricity and their potential applications in wearable electronics. High‐performance poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Tellurium (Te) composite TE fibers have been successfully developed via a continuous wet‐spinning approach followed by sulphuric acid treatment. With a simple pre‐modification to Te nanowires, the inorganic Te fillers form uniform distribution in PEDOT:PSS. At the optimal condition, the composite fibers exhibit a power factor of 233.5 µW m−1 K−2 and mechanical strength of 205 MPa, which are among the highest values reported so far for the PEDOT:PSS‐based TE fibers. From the viewpoint of TE property enhancement mechanism, understanding the morphology and carrier transport behavior in the 1D organic/inorganic composite fibers remains still challenging. On basis of a series of PEDOT:PSS/Te composite fibers with varying Te fractions, orientations of both the inorganic and organic constituents are quantitatively evaluated. Their electrical conductivities and Seebeck coefficients are also analyzed with modified series‐parallel models and energy filtering theory. This work may not only provide a universal approach to produce high‐performance organic/inorganic composite TE fibers for various wearable applications, but also help to understand the morphology and charge transport between heterogeneous phases in a 1D composite.

Nucleation and property enhancement mechanism of robust and high-barrier PLA/CNFene composites with multi-level reinforcement structure

The demand for biopolymer-based green packaging has attracted growing attention because of its outstanding properties and consistency with clean environmental principle, unfortunately, its slow crystallization rate and narrow processing window are challenging. Inspired by combined functions in nanocellulose-based conductive hybrids, this work developed high-performance polylactic acid (PLA) composites using conductive cellulose nanofiber (CNFene). Interestingly, CNFene has multiple functions as highly graphitized carbon and abundant hydroxyl groups, delivering stimulating properties to PLA composites. As nucleating agents, 3 wt% CNFene has a carbon layer on the surface combined with a hydrogen bonding network synergistically enhancing the tensile and crystallization properties of PLA-C3, with a tensile strength of ∼ 53.7 MPa, crystallinity of ∼ 33.9 %, and 6.6 °C decrease in the cold crystallization temperature. Additionally, the compatibility between CNFene and PLA can form a multi-level “reinforcement” network structure, further improving thermal stability and barrier properties. The resultant PLA-C3 showed higher thermal decomposition onset temperature (T0), wider melt-processing window (197.6 °C) and extremely lower overall migration levels in ethanol (68.6 μg/kg) and isooctane (16.3 μg/kg), due to that improved interaction between CNFene and PLA positively affects crystallization ability and kinetic/mechanism of PLA to meet the requirements of industrial and green biopackaging applications.

Origin of large piezoelectricity in BF-BT based multiphase ferroelectrics

Bismuth ferrite-barium titanate (BF-BT) based ferroelectrics with multi-phase coexistence exhibit promising piezoelectricity, while whose physical mechanism of property enhancement is poorly understood. In the present work, the Rayleigh law, in-situ electric field dependent synchrotron X-ray diffraction and ex-situ piezo-response force microscopy were utilized to gain insight into the property and structure evolution characteristics under electric fields. Extrinsic contribution from domain wall motion was regarded as the major determiner in piezoelectricity of the 0.69Bi1.05Fe0.99Sc0.01O3-0.3BaTiO3-0.01Bi1.05(Zn0.5Hf0.5)O3 ferroelectrics with rhombohedral and pseudo-cubic phase coexistence, different from those proposed structural origins in BF-BT based relaxor ferroelectrics (with high BT content) with large strain response. By analyzing the property discrepancy between unpoled and poled samples, the enhanced polarization and electro-strain in poled ceramics were attributed to the activated domain state induced by the direct current pre-poling.

Insight into the Property Enhancement Mechanism of Chemically Prepared Multi-Main-Phase (Nd,Ce)2Fe14B.

Nd2Fe14B has attracted intensive attention because of its excellent magnetic properties since 1980s. However, large demands for the expensive rare earth (mainly refers to Nd/Pr/Dy) limit its wider applications. Investigations of Ce-doped Nd2Fe14B have been attempted recently and multi-main-phase (MMP) (Nd,Ce)2Fe14B provides a promising way for the preparation of high-performance Ce-doped permanent magnets even though the inner mechanism has not been absolutely understood. We synthesized Ce-doped Nd2Fe14B nanostructures by the chemical method and successfully realized the obvious property enhancement of the MMP sample compared with that of the single-main-phase one. The coercivity of the MMP nanostructures is nearly 4.5 kOe with a remanence ratio of 0.36 before magnetic orientation, which is much larger than that of the SMP sample (1.7 kOe and 0.21), respectively. The property enhancement mechanism of the MMP sample analyzed mainly by first-order reversal curves could be concluded in three aspects: first, the content of α-Fe will be decreased; hence, the difficulty of the magnetic nucleation is increased. Second, the exchange coupling effect between the adjacent magnetic structures will be strengthened significantly. Last, the grain boundary phases with various magnetic features are formed, enhancing the magnetic pinning effect and specially tuning the inner interactions. This work is helpful for the deeper understanding of the property enhancement mechanism in MMP nanomagnets and provides an instructive way for the effective design and preparation of high-performance MMP Ce-doped Nd2Fe14B nanomagnets.

Low Interface Energies Tune the Electrochemical Reversibility of Tin Oxide Composite Nanoframes as Lithium-Ion Battery Anodes.

The conversion reaction of lithia can push up the capacity limit of tin oxide-based anodes. However, the poor reversibility limits the practical applications of lithia in lithium-ion batteries. The latest reports indicate that the reversibility of lithia has been appropriately promoted by compositing tin oxide with transition metals. The underlying mechanism is not revealed. To design better anodes, we studied the nanostructured metal/Li2O interfaces through atomic-scale modeling and proposed a porous nanoframe structure of Mn/Sn binary oxides. The first-principles calculation implied that because of a low interface energy of metal/Li2O, Mn forms smaller particles in lithia than Sn. Ultrafine Mn nanoparticles surround Sn and suppress the coarsening of Sn particles. Such a composite design and the resultant interfaces significantly enhance the reversible Li-ion storage capabilities of tin oxides. The synthesized nanoframes of manganese tin oxides exhibit an initial capacity of 1620.6 mA h g-1 at 0.05 A g-1. Even after 1000 cycles, the nanoframe anode could deliver a capacity of 547.3 mA h g-1 at 2 A g-1. In general, we demonstrated a strategy of nanostructuring interfaces with low interface energy to enhance the Li-ion storage capability of binary tin oxides and revealed the mechanism of property enhancement, which might be applied to analyze other tin oxide composites.

Synthesis of several enhanced ions doped yttrium&gadolinium oxide red phosphors by a polyethyleneglycol-assisted co-precipitation solution method

The red-emitting (Y0.92−x−y−z,Gd x )2O3:Eu3+,yBi3+,zLi+ phosphors have been synthesized via a polyethyleneglycol (PEG)-assisted co-precipitation solution method. The X-ray diffraction (XRD) patterns showed that the obtained samples crystallized in a cubic crystal system with space group I a 3(206) (a = 1.0604 nm) and Eu3+, Gd3+, Bi3+,Li+ ions could be well doped into the substrate. It is shown in the scanning electron microscopy (SEM) images that the particles with approximately spherical or regular small block in morphology, the average crystallite size was calculated to be 300–500 nm and the PEG-assisted sample showed better dispersancy. The photoluminescence spectra and fluorescence decay curves indicated that the phosphors could be excited by 254 and 395 nm, the emission intensity and color purity could be improved with the doping of moderate Gd3+, Bi3+ and Li+ and the lifetime decreased a lot with the co-doping of Gd3+ and Bi3+, which may expand the application of the phosphors. The optimal addition concentrations of Gd3+, Bi3+, Li+ were 20, 2 and 5 mol%. Furthermore, the action mechanism of PEG and luminous property enhancement mechanism of Gd3+, Bi3+ and Li+ were discussed in the present work.

Effects of transglutaminase catalyzed crosslinking on physicochemical characteristics of arachin and conarachin-rich peanut protein fractions

Arachin and conarachin-rich fractions of peanut protein were extracted by using cryoprecipitation followed by centrifugation. These two fractions were individually crosslinked using transglutaminase (TG). The physicochemical characteristics including aggregation due to crosslinking, solubility, thermal denaturation temperature (Td) and denaturation enthalpy (△H), morphology of microstructure and surface hydrophobicity (H0) of TG-treated and untreated arachin and conarachin-rich fractions were determined. The relative contents of arachin and conarachin in arachin and conarachin-rich fractions were 75% and 65%, respectively. Conarachin-rich fractions were found to more conveniently aggregate than arachin-rich from the results of SDS-PAGE. The solubility of treated arachin and conarachin-rich fractions was decreased by 66.13% and 36.91%, respectively. Only marginal increase in Td was observed in the case of crosslinked arachin-rich fraction while significant increase in Td (of the order of 10°C) was observed in crosslinked conarachin-rich fraction. The H0 values of both crosslinked arachin and conarachin-rich fractions decreased significantly. The treated arachin and conarachin-rich fractions had more compact microstructure compared to their untreated samples. Hence, the comparison of arachin and conarachin-rich in crosslinking and the mechanism of properties enhancement by TG is the aim of the research.

Understanding the property enhancement mechanism in exfoliated graphite nanoplatelets reinforced polymer nanocomposites

The focus of this study is to understand how exfoliated graphite nanoplatelets (xGnP) alter the elastic response of semi-crystalline polymers and reveal the mechanisms responsible for the property enhancement observed in graphite reinforced polymer nanocomposites. The nanocomposites were made by coating of polyamide 12 (PA12) powder with xGnP followed by melt compounding and injection molding. The mechanical properties, including tensile strength and modulus, flexural strength, and thermo-mechanical properties such as the glass transition temperature (T g) and loss modulus of the xGnP/PA12 nanocomposites, were determined as a function of the xGnP content. It was found that xGnP acted as nucleating agent for PA12 and significantly altered the physical properties of the polymers including T g and crystallization characteristics. Morphological studies indicated formation of xGnP agglomerates at xGnP content as low as 3 wt.%. A strong correlation between the T g and the tensile modulus in xGnP–PA12 was determined revealing presence of secondary reinforcing mechanisms in xGnP reinforced semi-crystalline polymer nanocomposites.

Antiferroelectric–ferroelectric phase boundary enhances polarization extension in rhombohedral Pb(Zr,Ti)O3

The main mechanism of properties enhancement in the morphotropic phase boundary region separating tetragonal and rhombohedral phases of Pb(Zr1-xTix)O3 (PZT) is related to polarization rotation. It is shown here that in proximity of the morphotropic phase boundary separating antiferroelectric and rhombohedral phases (near x = 0.1) and at elevated temperatures the properties are dominated by polarization extension. These results may provide a guideline for developing alternative piezoelectric materials to PZT.

Effect of Pb and Sn Additions on the Ductility of Cast AZ61 Mg Alloy

AZ61 alloy is an important magnesium (Mg) alloy which can be rolled at elevated temperature. However, the insufficient ductility of as-extruded alloys limits their design and applications. Pb or Pb+Sn additions lead to a high ductility (~18% at room temperature) and good tensile strength (~250 MPa). This paper discusses the mechanism of property enhancement and the influence of Pb addition on the solidification process of AZ61 alloy.

Effects of titanium addition on mechanical and corrosion behaviours of AZ91 magnesium alloy

The mechanical properties and corrosion behaviour of AZ91 magnesium alloy containing 0.2–0.5 wt.% Ti were investigated in this study. Results demonstrate that the enhancement of the ultimate tensile strength by 18% and yield strength by 47% can be achieved by Ti addition. The corrosion behaviour was evaluated by immersion tests and potentiodynamic polarisation measurements in 3.5% NaCl solution. The results from the immersion tests and potentiodynamic polarisation measurements showed that the corrosion resistance of AZ91 alloy increased progressively with the increase of the Ti content of the alloy. Compared to AZ91 alloy, 0.5Ti addition increased the corrosion resistance by up to 45 fold. The mechanism of property enhancement is ascribed to both the suppression of partially divorced β-Mg 17Al 12 eutectics and an increased Al content in α-Mg solid solution by Ti addition in AZ91 alloy.

A morphotropic phase boundary system based on polarization rotation and polarization extension

Many ferroelectric solid solutions exhibit enhanced electromechanical properties at the morphotropic boundary separating two phases with different orientations of polarization. The mechanism of properties enhancement is associated with easy paths for polarization rotation in anisotropically flattened free energy profile. Another mechanism of properties enhancement related to free energy flattening is polarization extension. It is best known at temperature-driven ferroelectric-paraelectric phase transitions and may lead to exceedingly large properties. Its disadvantage is temperature instability of the enhancement. In this paper a temperature-composition phase diagram is proposed that exhibits compositionally driven-phase transitions with easy paths for both polarization rotation and polarization extension.

Improvement of mechanical and corrosion properties of magnesium alloy by lead addition

Mechanical properties and corrosion behaviour of AZ91 magnesium alloy containing 0.2–1.0 wt.% Pb were investigated. An enhancement of ultimate tensile strength by 42%, yield strength by 58% and elongation by 20% can be achieved by Pb addition. Corrosion resistance of the AZ91 alloy also increased progressively with increasing Pb content. The mechanism of property enhancement is ascribed to the suppression of intermetallic phases (β-Mg 17Al 12 and α-Mg + β eutectic) by Pb addition.