Modular Surface Research Articles

Graphene‐Induced Surface Softening and Nanostructure Evolution of Platinum Foils

While it has been previously accepted that graphene growth on metal films by chemical vapor deposition (CVD) protects the surfaces by stiffening and hardening, in this study, an unusual opposite effect is reported. Herein, we use nanoindentation to study the mechaniported. Herein, we use nanoindentation to study the mechanical behavior of graphene‐covered platinum foils. Two graphene growth recipes using undiluted and diluted methane flow are studied, aiming to achieve a bulk or a surface‐mediated graphene growth mechanism, respectively. Contrary to previous reports, a 17% decrease is observed in the elastic modulus of the Pt surfaces when covered by graphene compared to graphene‐free regions for both recipes, when using the real indentation contact area extracted via atomic force microscopy (AFM) for the estimation. By performing cross‐sectional transmission electron microscopy (TEM), subsurface multilayers responsible for the decrease in stiffness are revealed and these observations and the mechanism of layer formation are explained. Hence, in this study, it is highlighted that surface stiffening of metals by graphene CVD has exceptions, especially in the case of metals with high carbon solubility. Moreover, in this study, approaches for combining cross‐sectional TEM, topological scans from AFM, and raw load–displacement data from nanoindentation to provide a complete, multiscale elucidation of the mechanical behavior of a material surface are described.

Falling weight impact acceleration-time signals analysis for road modulus detection: Theoretical and experimental investigations

Structural modulus detection is essential for construction and maintenance in road engineering. Falling weight impact loading method has significant strengths in large-scale, continuous, and rapid detection. To provide theoretical support for this, theoretical analysis and falling weight impact experiments were employed in this study to investigate the influence of road structure parameters and falling weight impact parameters on impact acceleration-time signals. First, the applicability of the Hertz model in road detection was analyzed, and theoretical formulas for peak acceleration amax and impact duration t2 were established, considering the perfectly elastic collision between falling weight and half-space. Second, the influence of layered structures’ properties on impact acceleration-time curves was studied through model box impact experiments. Third, field tests were conducted to study engineering applications. The results showed that the influence patterns were similar in both theoretical and experimental studies, with differences reflected in the time of compression and restitution phases due to the road materials’ viscosity and plasticity. Additionally, in indoor experiments, amax showed an excellent power function relationship with structural layer modulus, with R2 more than 0.95, and the contribution of each layer’s modulus to amax decreased from top to bottom. Finally, amax and resilient modulus of an old road also followed a good power function relationship, with R2 around 0.76. This study revealed that amax was recommended for road surface modulus detection based on solid theoretical and experimental support.

The Influence of Dew Retting on the Mechanical Properties of Single Flax Fibers Measured Using Micromechanical and Nanomechanical Approaches

The mechanical properties of single flax fibers are characterized here as a function of dew retting. The fibers are measured using micromechanical and nanomechanical techniques over a large retting period (91 days). Damage-free single flax fibers in various stages of dew retting were manually extracted from retted flax plant stems. The flexural modulus and strength of the flax fibers were determined using micromechanical methods. The effective modulus of the outer surface of the single fibers was measured using AFM-based nanoindentation. The micromechanical methods revealed that the flexural modulus and strength of the manually extracted single fibers does not vary significantly as the retting progresses. The micromechanical methods revealed two distinct values of flexural strength in the fibers attributed to different failure modes. The values of these strengths do not vary significantly with retting or over-retting. The nanomechanical methods revealed that the effective modulus of the outer surface of the single fibers does evolve with retting. The physical/chemical origin of these observations remains to be established and could be the objective of future work.

The Prime Geodesic Theorem in Arithmetic Progressions

Abstract We address the prime geodesic theorem in arithmetic progressions and resolve conjectures of Golovchanskiĭ–Smotrov (1999). In particular, we prove that the traces of closed geodesics on the modular surface do not equidistribute in the reduced residue classes of a given modulus.

Modeling and Assessment of Temperature and Thermal Stress Field of Asphalt Pavement on the Tibetan Plateau

The Qinghai–Tibet Plateau (QTP) is the highest altitude plateau in the world, characterized by strong solar radiation and large diurnal temperature differences and so on, which brings a great negative impact on the temperature and thermal stress field of asphalt pavement. The purpose of this study is to analyze the temperature field and thermal stress status of asphalt pavement in the QTP to provide a reference for pavement design and maintenance in high-altitude areas. The finite element method was applied to establish the temperature field model to study the distribution and variation of pavement temperature. On this basis, the influence of cooling amplitude on pavement thermal stress was studied during cold waves. In addition to this, the key internal factors affecting the thermal stress of pavement, such as surface thickness, surface temperature shrinkage coefficient, surface modulus, and base modulus, were analyzed by an orthogonal test. It was found that temperature and solar radiation have a significant effect on the pavement temperature field. When the cold wave came, the cooling rate had a considerable impact on the thermal stress of the pavement, that is, every 5 °C increase in cooling rate would increase the thermal stress by more than 50%. The temperature shrinkage coefficient and surface modulus of the surface layer material had the greatest influence on the pavement thermal stress. The thermal stress could be reduced by more than 0.4 Mpa for every 5 × 10−6/°C reduction in the surface temperature shrinkage coefficient or every 1000 Mpa reduction in the surface modulus. This study can provide a reference for improving the temperature field and thermal stress field of asphalt pavement in the plateau area.

Promoting bone regeneration with liquid crystal bone cement from a new perspective: Inhibiting BMSCs PANoptosis under aseptic inflammation

PANoptosis has become an important way to systematically analyses and address extensive crosstalk and common regulatory targets between different programmed cells death pathways. Focusing on the PANoptosis of bone marrow mesenchymal stem cells (BMSCs) induced by implants would be an encouraging way to improve cells survival and bone regeneration. In this study, we designed a liquid crystal hydrogel bone cement GelHap/TCLC, through phase state bionic to mimic the dynamic viscoelastic microenvironment of bone, to downregulate cells PANoptosis, wherein mouse monocyte-macrophages mouse macrophages (RAW264.7) and BMSCs were cocultured on the bone cement to simulate an immune-inflammatory state. Results showed that the liquid crystal hydrogels possessed a surface modulus of 80 ± 6.62 kPa, close to the natural bone matrix. PANoptosis of BMSCs was reduced with cells survival rate of 90.7 ± 2.3 %, which was higher than 83.1 ± 1.7 % of nonliquid crystal GelHap and 72.9 ± 2.9 % of commercial bone cement. Notably, the BMSCs PANoptosis executioners were inhibited obviously than the control. In addition, osteogenic differentiation in vitro and bone regeneration in vivo (BV/TV = 28.80 ± 1.09 % at week 8) were promoted. This study bridges the gap between bone implants and BMSCs programmed death from a more systematic perspective, complements the liquid crystal state theory governing the fate of stem cell death in a broader sense, provides a class of biomimetic tissue engineering materials to solve the problem of BMSCs survival caused by aseptic inflammation induced by implants.

Effect of N plasma immersion ion implantation (N-PIII) on the microstructure and mechanical properties of 8Cr4Mo4V steel

To enhance the surface hardness and wear resistance of 8Cr4Mo4V steel, nitrogen plasma immersion ion implantation (N-PIII) was carried out, under various nominal implantation energies, in this study. Additionally, the microstructure and mechanical properties of the steel were analyzed. The results indicated that the depth of the nitrogen ion-implanted layer escalated with the specified implantation energy, reaching 140 nm for a 50 keV sample. Nitrogen was present within the implanted layer in the martensite lattice as a solute, and also in the form of nitrides along with alloying elements. Moreover, a nanocrystalline layer approximately 40–70 nm thick also formed at the sample surface. As the implantation energy increased, both the surface roughness and residual stress of the sample initially increased before declining, whereas the surface hardness and modulus exhibited a gradual increase. After the 50 keV N-PIII treatment, the surface hardness of the sample increased by 39 %, which caused a remarkable reduction in the friction coefficient, and the wear amount was also reduced by about 40 %. This work systematically establishes the relationship between the surface microstructures, surface morphology, and mechanical properties of implanted 8Cr steel, and significantly improves its surface hardness and wear resistance.

Extreme Fast Charging of Lithium Metal Batteries Enabled by a Molten-Salt-Derived Nanocrystal Interphase.

The extreme fast charging performance of lithium metal batteries (LMBs) with a long life is an important focus in the development of next-generation battery technologies. The friable solid electrolyte interphase and dendritic lithium growth are major problems. The formation of an inorganic nanocrystal-dominant interphase produced by preimmersing the Li in molten lithium bis(fluorosulfonyl)imide that suppresses the overgrowth of the usual interphase is reported. Its high surface modulus combined with fast Li+ diffusivity enables a reversible dendrite-proof deposition under ultrahigh-rate conditions. It gives a record-breaking cumulative plating/stripping capacity of >240000 mAh cm-2 at 30mA cm-2@30 mAh cm-2 for a symmetric cell and an extreme fast charging performance at 6 C for 500 cycles for a Li||LiCoO2 full cell with a high-areal-capacity, thus expanding the use of LMBs to high-loading and power-intensive scenarios. Its usability both in roll-to-roll production and in different electrolytes indicating the scalable and industrial potential of this process for high-performance LMBs.

Norm bounds on Eisenstein series

We study the sup-norm bound (both individually and on average) for Eisenstein series on certain arithmetic hyperbolic orbifolds producing sharp exponents for the modular surface and Picard 3-fold. The methods involve bounds for Epstein zeta functions, and counting restricted values of indefinite quadratic forms at integer points.

Wall crossing for K‐moduli spaces of plane curves

AbstractWe construct proper good moduli spaces parametrizing K‐polystable ‐Gorenstein smoothable log Fano pairs , where is a Fano variety and is a rational multiple of the anticanonical divisor. We then establish a wall‐crossing framework of these K‐moduli spaces as varies. The main application in this paper is the case of plane curves of degree as boundary divisors of . In this case, we show that when the coefficient is small, the K‐moduli space of these pairs is isomorphic to the GIT moduli space. We then show that the first wall crossing of these K‐moduli spaces are weighted blow‐ups of Kirwan type. We also describe all wall crossings for degree 4,5,6 and relate the final K‐moduli spaces to Hacking's compactification and the moduli of K3 surfaces.

Resist Thermal Shock Through Viscoelastic Interface Encapsulation in Perovskite Solar Cells

Enhancing the lifetime of perovskite solar cells (PSCs) is one of the essential challenges for their industrialization. Although the external encapsulation protects the perovskite device from the erosion of moisture and oxygen under various harsh conditions. However, the perovskite devices still undergo static and dynamic thermal stress during thermal and thermal cycling aging, respectively, resulting in irreversible damage to the morphology, component, and phase of stacked materials. Herein, the viscoelastic polymer polyvinyl butyral (PVB) material is designed onto the surface of perovskite films to form flexible interface encapsulation. After PVB interface encapsulation, the surface modulus of perovskite films decreases by nearly 50%, and the interface stress range under the dynamic temperature field (−40 to 85 °C) drops from −42.5 to 64.8 MPa to −14.8 to 5.0 MPa. Besides, PVB forms chemical interactions with FA+ cations and Pb2+, and the macroscopic residual stress is regulated and defects are reduced of the PVB encapsulated perovskite film. As a result, the optimized device's efficiency increases from 22.21% to 23.11%. Additionally, after 1500 h of thermal treatment (85 °C), 1000 h of damp heat test (85 °C & 85% RH), and 250 cycles of thermal cycling test (−40 to 85 °C), the devices maintain 92.6%, 85.8%, and 96.1% of their initial efficiencies, respectively.

Cytocompatibility of electrospun poly-L-lactic acid membranes for Bruch's membrane regeneration using human embryonic stem cell-derived retinal pigment epithelial cells.

Cell replacement therapy is under development for dry age-related macular degeneration (AMD). A thin membrane resembling the Bruch's membrane is required to form a cell-on-membrane construct with retinal pigment epithelial (RPE) cells. These cells have been differentiated from human embryonic stem cells (hESCs) in vitro. A carrier membrane is required for cell implantation, which is biocompatible for cell growth and has dimensions and physical properties resembling the Bruch's membrane. Here a nanofiber electrospun poly-L-lactic acid (PLLA) membrane is tested for capacity to support cell growth and maturation. The requirements for laminin coating of the membrane are identified here. A porous electrospun nanofibrous PLLA membrane of ∼50 nm fiber diameter was developed as a prototype support for functional RPE cells grown as a monolayer. The need for laminin coating applied to the membrane following treatment with poly-L-ornithine (PLO), was identified in terms of cell growth and survival. Test membranes were compared in terms of hydrophilicity after laminin coating, mechanical properties of surface roughness and Young's modulus, porosity and ability to promote the attachment and proliferation of hESC-RPE cells in culture for up to 8 weeks. Over this time, RPE cell proliferation, morphology, and marker and gene expression, were monitored. The functional capacity of cell monolayers was identified in terms of transepithelial electrical resistance (TEER), phagocytosis of cells, as well as expression of the cytokines, vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF). PLLA polymer fibers are naturally hydrophobic, so their hydrophilicity was improved by pretreatment with PLO for subsequent coating with the bioactive protein laminin. They were then assessed for amount of laminin adsorbed, contact angle and uniformity of coating using scanning electron microscopy (SEM). Pretreatment with 100% PLO gave the best result over 10% PLO treatment or no treatment prior to laminin adsorption with significantly greater surface stiffness and modulus. By 6 weeks after cell plating, the coated membranes could support a mature RPE monolayer showing a dense apical microvillus structure and pigmented 3D polygonal cell morphology. After 8 weeks, PLO (100%)-Lam coated membranes exhibited the highest cell number, cell proliferation, and RPE barrier function measured as TEER. RPE cells showed the higher levels of specific surface marker and gene expression. Microphthalmia-associated transcription factor expression was highly upregulated indicating maturation of cells. Functionality of cells was indicated by expression of VEGF and PEDF genes as well as phagocytic capacity. In conclusion, electrospun PLLA membranes coated with PLO-Lam have the physical and biological properties to support the distribution and migration of hESC-RPE cells throughout the whole structure. They represent a good membrane candidate for preparation of hESC-RPE cells as a monolayer for implantation into the subretinal space of AMD patients.

Surface modification of nitrocellulose by interfacial self-assembly of metal-phenolic network for enhanced thermal stability and eco-friendly propulsion energy

Metal-phenolic networks (MPNs) have received widespread interest owing to their ability to incorporate metal ions and phenolic ligands in a modular manner. However, the effect of MPNs on nitrocellulose (NC), an energetic material for propulsion, has not been extensively investigated. Herein, we fabricated MPN-coated NC fibers (NC@MPN) and confirmed the successful coating and homogeneous distribution of MPN on the surface of NC through Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, scanning electron microscopy (SEM) and Energy Dispersive spectroscopy (EDS). The thermal stability of NC was enhanced as evidenced by differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC) and the ignition point test. The thermal decomposition activation energy of NC@MPN can reach 200.73 kJ•mol−1, 7.50 % higher than that of NC primitive fiber (186.72 kJ•mol−1). The ARC tests demonstrate that the implementation of MPN coating prolonged the time of entering the adiabatic section by 5.4 °C and the forecast temperatures for TD8 and TD24 have increased by 4.6 and 4.8 °C, respectively. Additionally, the ignition point was also raised by 2 °C. The aforementioned three experimental results provide evidence for the enhanced thermal stability conferred by MPNs. Besides, thermogravimetric analysis (TGA) results demonstrate a reduction in the residue from thermal decomposition. The present study presents a simple and robust coating strategy for the modular surface engineering of energetic materials, which significantly improves thermal stability and reduces the residues of thermal decomposition.

Counting and Equidistribution of Reciprocal Geodesics and Dihedral Groups

Abstract We study the growth of the number of conjugacy classes of infinite dihedral subgroups of lattices in $\operatorname{PSL}_{2}{\mathbb{R}}$, generalizing the earlier work of Sarnak [ 9] and Bourgain–Kontorovich [ 4] on the growth of the number of reciprocal geodesics on the modular surface. We also prove that reciprocal geodesics are equidistributed in the unit tangent bundle.

Framed parabolic sheaves on a trinion

We consider for structure groups [Formula: see text] a densely defined toric structure on the moduli space of framed parabolic sheaves on a three-punctured sphere, which degenerates to an actual toric structure. In combination with previous degeneration results, these extend to similar moduli for arbitrary Riemann surfaces.

Evaluating the Effect of Different Mouthrinses on Properties of the Enamel and Dental Composite Surfaces

This study investigated the effects of different solutions (artificial saliva, Listerine Cool Mint-alcohol containing and Colgate Plax-alcohol free) on the nanohardness, elastic modulus and surface roughness of enamel surface and composite materials (Admira Fusion, Clearfil Majesty Esthetic and Mosaic Universal). Specimens of 2 mm depth and 5 mm diameter were stored in solutions for 12 h at 37�C. Baseline and final measurements were obtained using a HYSITRON TI 950 TriboIndenter testing machine. The applied force to each specimen increased from 0 to 1000 �N. For SEM images, one sample in each group was covered with a thin layer of mix of gold and palladium using a sputter coater (Quorum Q150R ES, UK). Scanning electron microscopy (SEM) images were taken at 5000� magnifications to evaluate the surface morphology. Statistical analysis for hardness, elastic modulus and roughness was performed by Two-way ANOVA, Benferroni and Tukey HSD at a significance level 0.05. The results of this study showed that the highest value of surface roughness and lowest hardness and elastic modulus were presented by Admira (p[0.001). Listerine caused significantly increased surface roughness (p[0.001) and decreased hardness and elastic modulus parameters (p[0.001). The mouthrinse containing alcohol caused more significant changes in the nanohardness, elastic modulus, surface roughness values of enamel and composite surfaces.

Enhanced arc erosion and dynamic welding resistance of Ag-10 wt%Ni@Gr contact material

In this work, a novel hybrid reinforcement Ni@Gr was successfully synthesized by graphene in-situ grown on the surface of Ni particles, and the Ag-10 wt%Ni@Gr contact material was prepared by the combined methode of wet mixing and spark plasma sintering. The effect of graphene incorporation on the electrical performance of Ag-10 wt%Ni@Gr contact material was investigated, and the arc erosion mechanism was discussed as well. As compared to the Ag-10 wt%Ni contact material, the make-arc energy, break-arc energy and the maximum welding force of the Ag-10 wt%Ni@Gr contact material are decreased by 13.2 %, 4.9 %, and 23.1 %, respectively. Moreover, the Ag-10 wt%Ni@Gr contact material displays smaller erosion area, lower surface roughness and less mass loss. It can be ascribed to the increased elastic modulus of the contact surface, reduced bounce effect, lowered make-arc energy and shortened the make-arc duration that are stemmed from the incorporation of graphene. In addition, the incorporation of graphene contributes to the enhanced molten pool viscosity, which can effectively restrain Ag splashing, thereby enhancing arc erosion resistance and welding resistance.

Evaluation of the abilities of atomic oxygen/ultraviolet resistance for the filled silicone rubber coating: Structures, properties, and aging mechanism

A series of experimental techniques were used to study the erosion-damage effect of a silica-filled silicone rubber coating exposed to simulated space environment (atomic oxygen and ultraviolet irradiation). The elastomer is known to be chemically and thermally stable, but there are insufficient data on its durability in the space environment. In the present work, atomic oxygen doses up to 3.8 × 1021 atoms·cm−2 and ultraviolet irradiation doses up to 360 equivalent sun-hours (ESH) were applied from Space Environment Simulation Measurement System, respectively. Since the aging and failure processes of the filled silicone rubber relate to different aspects of chemical structure and physics form, therefore, this study explored the use of chemical-mechanics methods to comprehensively evaluate the erosion-damage effect of materials. Morphology and chemical changes due to radiation were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and nanoindentation test probed surface mechanical properties changed with exposure dose. Results demonstrated that, with increased exposure time and irradiation-induced free radicals，the aggregation state and molecular chain structure of the silica-filled silicone rubber have changed, which caused an increase in surface hardness and modulus. Taken together, the results indicated that oxidative cross-linking was the dominant degradation mechanism under the irradiation dose in this paper.

Structural Elucidation of Electrical and Optical Properties in Lead‐free Organic‐Inorganic Copper Bromide [(CH3)4N]2CuBr4 Single Crystals

AbstractOrganic‐inorganic metal halide single crystals have attracted a lot of attention due to their flexible structural design and excellent optoelectronic applications. This study details the synthesis of copper‐based [(CH3)4N]2CuBr4 hybrid metal halide single crystals via a slow evaporation method. The crystal structure, crystal habit, chemical groups, intermolecular interactions, electrical properties of the sample were studied via single crystal x‐ray diffraction, scanning electron microscopy, Raman and Fourier transform infrared spectrometer, Hirshfeld surface analysis, impedance spectroscopy, and modulus spectroscopy, respectively. An orthorhombic crystal system with the non‐centrosymmetric space group Pna21 was identified at room temperature. The deformation in the tetrahedra was calculated by the bond angle and bond length deformation index. The Cole‐Cole plot displayed the existence of depressed semicircles, which indicated the predominant distribution of grains, further confirmed by the SEM image. The deformed semi‐circular arcs on the electric modulus curve undeniably prove that the bulk effect dominates the material‘s electrical properties. Significantly, the compound presents a phase transition at ~240 K and excellent thermal stability up to a temperature of 400 K. Therefore, our research sheds light on the temperature dependence of electrical responses in these hybrid crystals and gives inspiration for the development of single crystal‐based efficient energy devices.

Rainfall Runoff and Nitrogen Loss Characteristics on the Miyun Reservoir Slope

Rainfall intensity and slope gradient are the main drivers of slope surface runoff and nitrogen loss. To explore the distribution of rainfall runoff and nitrogen loss on the Miyun Reservoir slopes, we used artificial indoor simulated rainfall experiments to determine the distribution characteristics and nitrogen migration paths of surface and subsurface runoff under different rainfall intensities and slope gradients. The initial runoff generation time of subsurface runoff lagged that of surface runoff, and the lag time under different rainfall intensity and slope conditions ranges from 3.97 to 12.62 min. Surface runoff rate increased with increasing rainfall intensity and slope gradient; compared with a rainfall intensity of 40 mm/h, at a slope of 15°, average surface runoff rate at 60 and 80 mm/h increased by 2.38 and 3.60 times, respectively. Meanwhile, the subsurface runoff rate trended upwards with increasing rainfall intensity, in the order 5 > 15 > 10°. It initially increased and then decreased with increasing slope gradient, in the order 5 > 10 > 15°. Total nitrogen (TN) loss concentration of surface runoff shows a decrease followed by a stabilization trend; the concentration of TN loss decreases with decreasing rainfall intensity, and the stabilization time becomes earlier and is most obvious in 5° slope conditions. TN loss concentration in subsurface runoff decreased with increasing rainfall intensity, i.e., 40 > 60 > 80 mm/h. The surface runoff rainfall coefficient was mainly affected by rainfall intensity, a correlation between αs and slope gradients S was not obvious, and the fitting effect was poor. The subsurface runoff rainfall coefficient was mainly affected by slope gradient, the R2 of all rainfall intensities was <0.60, and the fitting effect was poor. The main runoff loss pathway from the Miyun Reservoir slopes was surface runoff, which was more than 62.57%. At the same time, nitrogen loss was subsurface runoff, more than 51.14%. The proportion of surface runoff to total runoff increases with the increase of rainfall intensity and slope, with a minimum of 62.57%, and the proportion of nitrogen loss from subsurface runoff also decreases with increasing rainfall intensity but does not change with slope gradient. The order of different runoff modulus types was mixed runoff (surface and subsurface runoff occur simultaneously) > surface runoff > subsurface runoff. The surface and mixed runoff modulus increased significantly with increasing rain intensity under different rain intensities and slope gradients. Overall, rainfall intensity significantly affected slope surface runoff, and slope gradient significantly affected nitrogen loss.