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Lead sulfide (PbS) presents large potential in thermoelectric application due to its earth‐abundant S element. However, its inferior average ZT (ZTave) value makes PbS less competitive with its analogs PbTe and PbSe. To promote its thermoelectric performance, this study implements strategies of continuous Se alloying and Cu interstitial doping to synergistically tune thermal and electrical transport properties in n‐type PbS. First, the lattice parameter of 5.93 Å in PbS is linearly expanded to 6.03 Å in PbS0.5Se0.5 with increasing Se alloying content. This expanded lattice in Se‐alloyed PbS not only intensifies phonon scattering but also facilitates the formation of Cu interstitials. Based on the PbS0.6Se0.4 content with the minimal lattice thermal conductivity, Cu interstitials are introduced to improve the electron density, thus boosting the peak power factor, from 3.88 μW cm−1 K−2 in PbS0.6Se0.4 to 20.58 μW cm−1 K−2 in PbS0.6Se0.4−1%Cu. Meanwhile, the lattice thermal conductivity in PbS0.6Se0.4−x%Cu (x = 0–2) is further suppressed due to the strong strain field caused by Cu interstitials. Finally, with the lowered thermal conductivity and high electrical transport properties, a peak ZT ~1.1 and ZTave ~0.82 can be achieved in PbS0.6Se0.4 − 1%Cu at 300–773K, which outperforms previously reported n‐type PbS. Cu interstitial doping is realized in n‐type PbS‐based thermoelectric material by expanding its lattice space, resulting in synergistically optimized carrier and phonon transport properties, thus contributing to a high ZTave value of 0.82 at 300–773 K.

Analogous to real spins, valleys as carriers of information can play significant roles in physical properties of two-dimensional Dirac materials. On the other hand, utilizing external periodic potential is an efficient method to manipulate their band structures and transport properties. In this work, we investigate the valley dependent optics-like behaviors based on an 8- Pmmn borophene superlattice with the transfer matrix method and effective band approach. Firstly, it is found that the band structure is renormalized, more tilted Dirac cones are generated, and the group velocities are modified by the periodic potentials. Secondly, due to the exotic tilted Dirac cones in 8- Pmmn borophene, a perfect valley selected angle filter can be realized. The electrons with a specific incident angle can transmit completely in an energy window, which is flexibly tunable by changing the periodic potential. Thirdly, by using the Green’s function to simulate the time evolution of wave packets, electrons can be shown to propagate without any diffraction, valley electron beam supercollimation happens by modulating the potential parameters. Different from the graphene superlattice, the electron supercollimation here is valley dependent and can be used as a valley electron beam collimator. Fourthly, we can tune the polarization and supercollimation angles by changing the superlattice direction. These intriguing results in an 8- Pmmn borophene-based superlattice offer more opportunities in diverse electronic transport phenomena and may facilitate the devices applications in valleytronics and electron-optics.

Human long bones exhibit pore size gradients with small pores in the exterior cortical bone and large pores in the interior cancellous bone. However, most current bone tissue engineering (BTE) scaffolds only have homogeneous porous structures that do not resemble the graded architectures of natural bones. Pore-size graded (PSG) scaffolds are attractive for BTE since they can provide biomimicking porous structures that may lead to enhanced bone tissue regeneration. In this study, uniform pore size scaffolds and PSG scaffolds were designed using the gyroid unit of triply periodic minimal surface (TPMS), with small pores (400 μm) in the periphery and large pores (400, 600, 800 or 1000 μm) in the center of BTE scaffolds (designated as 400-400, 400–600, 400–800, and 400–1000 scaffold, respectively). All scaffolds maintained the same porosity of 70 vol%. BTE scaffolds were subsequently fabricated through digital light processing (DLP) 3D printing with the use of biphasic calcium phosphate (BCP). The results showed that DLP 3D printing could produce PSG BCP scaffolds with high fidelity. The PSG BCP scaffolds possessed improved biocompatibility and mass transport properties as compared to uniform pore size BCP scaffolds. In particular, the 400–800 PSG scaffolds promoted osteogenesis in vitro and enhanced new bone formation and vascularization in vivo while they displayed favorable compressive properties and permeability. This study has revealed the importance of structural design and optimization of BTE scaffolds for achieving balanced mechanical, mass transport and biological performance for bone regeneration. [Display omitted] •Graded scaffolds with controllable pore size distributions were provided.•Developed high-performance scaffolds via structural optimization and 3D printing.•Pore size graded (PSG) scaffolds improved mass transport properties.•PSG scaffolds enhanced osteogenesis in vitro and neovascularization in vivo.

Unlike tremendous works on the electronic structures of tetradymite compounds, studies of their thermal properties are relatively rare. Here, first-principles calculations and Boltzmann theory are combined to investigate the phonon transport of such kind of layered materials. Using four binary tetradymites as prototypical examples, it is interesting to find that the weak van der Waals (vdW) interactions play an important role in determining their lattice thermal conductivities, which are obviously higher than those without the consideration of vdW, especially for the out-of-plane direction. In principle, such enhanced phonon transport can be attributed to the decreased interlayer spacing caused by the presence of vdW, which effectively reduces the strong anharmonicity of the systems. Indeed, we observe relatively smaller Grüneisen parameter together with larger phonon group velocity and relaxation time. Our theoretical work demonstrates the vital importance of the seemingly weak vdW forces in predicting the phonon transport properties of various layered structures.

In this paper, the microstructure and resistance to chloride ion penetration of ultra-high-performance concrete (UHPC) prepared from lightweight aggregate (LWA) were studied through simulation and experiment. The effects of LWA with different particle sizes on the chloride ion transport properties of lightweight ultra-high-performance concrete (L-UHPC) were discussed through simulation test results. The random delivery model of LWA in L-UHPC was established by MATLAB, and the model was introduced into COMSOL. Through the comparative analysis of experimental data and simulation results, the repeatability of the proposed model and the simulation accuracy were verified. The results show that when the LWA particle size changes from 0.15–4.75 mm to 0.15–1.18 mm, the width of interfacial transition zone (ITZ) and the overall porosity of L-UHPC decrease. This is because the large particle size LWA has more open pores with larger pore diameters and related interconnections, which are potential channels for chloride ion transport. Therefore, the chloride ion transport properties in L-UHPC are inhibited, which is manifested by the “tortuosity effect” of the LWA.

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings.

Solid polymer electrolytes based on polyvinyl alcohol (PVA)-chitosan (CS) polymer blend and Li-salt doped blend electrolyte films are prepared using the solution cast technique. The Fourier transform infrared spectra showed that the absorption peaks shifted in Li-salt doped polymer blend composites compared to pure blend films: indicating the chemical modifications upon doping. From the UV-visible spectra, the spectral absorption response of Li+ salt-doped polymer blend composites showed a red shift in the absorption band. The optical band gap of the pure polymer blend decreased upon doping. X-ray diffraction studies showed the dopant-dependent structural modification of pure polymer blend upon doping. SEM images also showed the change in the surface morphology of the pure polymer blend upon doping. The termogravimetric analysis study revealed that the thermal stability of the pure polymer blend increases with Li2CO3 concentration. The ionic conductivity of PVA-CS increases with Li-salt concentration, and the maximum conductivity of 7.70·10-5 S·cm-1 is observed for 15 wt% of Li2CO3 salt concentration. The transport property study revealed that the ions are the majority conducting charge carriers in polymer blend composite.

The multiphase distribution and transport properties in porous media are strongly influenced by capillary pressure and rock–fluid interactions. The influence of nano-scale wetting film caused by the disjoining pressure on the multiphase transport properties is not fully considered in the current pore scale modeling methods, and it is unclear how the nano-scale wetting film influences the transport behavior at different porous media scale. In this study, we propose a multiphase pore network transport model that considers capillary pressure, disjoining pressure (the latter arising only in fluid films on solid surfaces) and fluid transport mechanisms in irregular pores. The thickness of nano-scale wetting film under multiphase conditions in irregular pores is calculated based on the force balance between capillary pressure and disjoining pressure resulting from van der Waals force, electric double-layer interactions and structural force. The gas displacing water process is simulated in a water-wet 3D unstructured pore network extracted from 3D-reconstructed digitized shale image. The influence of nano-scale wetting film on essential transport properties including relative permeability, capillary pressure curve and resistivity index is analyzed, and its variation is elucidated for different porous media length scales. Notably, the nano-scale wetting film enhances the wetting-phase relative permeability and electrical conductivity in nano-scale porous media, and the effect is way less important on micron-scale. We further conclude the deviation from the case without nano-scale water film can be attributed to the interplay of corner water transport area and nano-scale water film transport area in invaded pore throats by analyzing the wetting-phase distribution based on the proposed three microscopic parameters. We also found that the nano-scale wetting film causes more wetting fluid retention after displacement in nano-porous media, which possibly explains the low flowback rate after hydraulic fracturing in shale and ultra-tight sandstones. Article Highlights A multiphase pore network transport model that considers both capillary pressure and disjoining pressure is proposed. Nano-scale wetting film enhances the wetting phase relative permeability and electrical conductivity in nano-scale porous media. Nano-scale wetting film causes more wetting fluid retention after displacement in nanoporous media.

In this work, an investigation on hybrid gel polymer electrolytes (HGPEs) comprising of polymethyl methacrylate (PMMA)-polylactic acid (PLA) incorporated with lithium bis(trifluoromethanesulfony)imide (LiTFSI) was carried out. The HGPEs samples were characterized for their structural, thermal and ionic conduction properties via FTIR, XRD, DSC, and EIS. FTIR analysis showed the interaction between the PMMA-PLA hybrid polymer and LiTFSI through the appearance of peaks and peak shifts at the coordinating site on the polymer blend. The DSC analysis showed that the glass transition temperature (Tg) of HGPEs was decreased as the LiTFSI content increased, suggesting that the ion–dipole interaction decreased and led to the enhancement of the HGPEs system’s amorhous phase. The ionic conductivity was calculated based on the Cole–Cole plot and the incorporation of 20 wt% LiTFSI into the hybrid polymer matrixes revealed that the maximum ionic conductivity was 1.02 × 10–3 S cm−1 at room temperature as the amorphous phase increased. The dissociation of ions and transport properties of the PMMA-PLA-LiTFSI systems was determined via the dielectric response approach and it was found that number density (ɳ), mobility (μ), and diffusion coefficient (D) of mobile ions followed the ionic conductivity trend.

Two-dimensional (2D) tungsten disulfide (WS2) is attracting increasing attention because of its excellent physical properties. However, the phonon scattering mechanisms of 2D T′-phase WS2 (T′-WS2) are still poorly understood. In this paper, we systematically evaluate the phonon thermal transport properties of monolayer T′-WS2 under different biaxial tensile and compressive strain using first-principles calculations. The lattice thermal conductivity (kl) of monolayer T′-WS2 decreases monotonically with the increase in biaxial strain. The largest reductions are 97.84% (7% tensile strain) and 65.41% (−3% compressive strain). The kl of monolayer T′-WS2 is dominated by acoustic phonon modes and a portion of optical phonon modes (0–8 THz). Moreover, from the analysis of phonon behaviors, the reduction in the kl of monolayer T′-WS2 under biaxial tensile strain is attributed to the decrease in phonon heat capacity, phonon group velocity, and phonon lifetime. However, for the biaxial compressive strain, the reduction in the kl can be attributed to the interaction among the increased phonon heat capacity, relatively complex changes in the phonon group velocity, and the reduced phonon lifetime. Therefore, according to the variations in phonon phase space and Grüneisen parameters, it is evident that the biaxial tensile strain does not have a significant effect on the phase space of monolayer T′-WS2, whereas it has a significant effect on the Grüneisen parameter. This investigation offers valuable insight into the thermal conduction behavior of 2D monolayer T′-WS2.