Simple Surface Research Articles

Impediment effect of two-dimensional graphene on gaseous fluorine permeation during direct fluorination of polyurethane

Direct fluorination with gaseous fluorine (F2) is a simple way to prepare fluorine-containing polymers, however, partial hydrolysis of CONH- group during fluorination process often reduces the bulk properties of fluorinated polyurethane (PU). Here, two-dimensional graphene (GE) as barrier layer was introduced into the thermoplastic polyurethane (TPU) matrix followed by fluorination treatment by F2 gas. The conjugated π structure of graphene limited excessive fluoridation of the GE/TPU sample, while the large aspect ratio restrained the diffusion and penetration of F2 gas in the bulk. As a result, rich F elements were accumulated on the surface with the slightly-fluorinated bulk. The fluorinated GE/TPU sample integrated the excellent mechanical properties of TPU with friction behaviors of fluorine-containing polymers. The initial friction coefficient was 0.5, 50% lower than the original GE/TPU while maintaining the unchanged mechanical modulus and thermal stability. This research may effectively solve the issue on performance degradation caused by partial hydrolysis of polymer materials containing CONH- group during fluorination process, providing a simple and effective surface modification strategy for preparing high-performance fluorine-containing TPU.

Deformation classification of quartic surfaces with simple singularities

We give a complete equisingular deformation classification of simple spatial quartic surfaces which are in fact K3 -surfaces.

High speed water droplet impact erosive behavior on dry and wet pulsed waterjet treated surfaces

During water droplet impact onto a dry or wet rough solid surface, several phenomena affect the surface erosion process, such as splashing, crown formation, and small droplet emission to name a few. These phenomena have been extensively studied for various simple target surface geometries. However, droplet impact studies on complex irregular and asymmetric target surface topographies resulting from a waterjet treatment have never been conducted. Furthermore, very limited reports are found on the role of target surface topography and water droplet deformation development on the resulting target stress state. In the present study, high speed droplet impingements on surfaces exhibiting coarse topographical features associated with ultrasonic pulsed waterjet treatment are modeled to understand the underlying mechanisms causing erosion. Impacts on surfaces with various roughness values and water film thicknesses are modeled using a three-dimensional coupled Eulerian–Lagrangian approach. A detailed comparative analysis of the model with experimental ultrasonic pulsed waterjet erosion features and material loss is provided. It was found that the synclastic curvature of the modeled coarse surface features increases the shock wave's strength as many compression wavelets are simultaneously emitted at each water droplet contact location with the surface, resulting in concentrated high-pressure zones. The ultrasonic pulsed waterjet treated surface features and water film thickness also greatly influence the onset of water droplet splashing, subsequent finger, secondary droplet characteristics, and crown stability. According to the numerical results, strong splashing patterns and droplet breakup are generated and create high stress zones capable of accelerating surface erosion, explaining the enhanced performance of ultrasonic pulsed waterjet process.

Local eutectic combined with surface functional treatment: An efficient strategy to lower desorption temperature of bulk magnesium-based hydride

Magnesium-based hydrides are ideal for hydrogen storage, but sluggish dehydrogenation kinetic and relative high operation temperature hindered their practical applications, especially for large particle hydrides. This study reports a novel surface engineering strategy combining local eutectic with functional treatment to substantially improve the desorption behavior of bulk metal hydride. A typical Mg-Ni-based composite, Mg90Ni10Hx, was prepared via a one-step gas–solid process, achieving a well-distributed core–shell microstructure. The as-synthesized Mg90Ni10Hx was subsequently treated with a simple surface functionalization, i.e., short-time hydrolysis. Results showed an exciting improvement in dehydrogenation kinetics: the peak dehydrogenation temperature decreased from 395 °C to 275 °C, and corresponding activation energy decreased from 114.3 to 59.0 kJ/mol H2, which is comparable to some nanoscaled hydrides with catalysts. Combined with density functional theory calculations, a potential mechanism was proposed: the Mg(OH)2 generated during hydrolysis can weaken Mg-H bond and induce the dehydrogenation by electrostatic interaction, and hydrogen atoms inside bulk hydrides continue to diffuse to the surface along the microcracks created by volume contraction of Mg2NiHx after dehydrogenation, allowing the bulk hydride to continue to dehydrogenate. The results provide alternative strategy to design high-reactive metal hydrides with low cost and extend our understanding of Mg(OH)2 in magnesium-based hydrides.

Migration of endothelial cells on the surface of anodized Ni-Ti stent strut.

Stent is widely regarded as the main treatment for curing cardiovascular diseases such as stenosis. Previous research has revealed that the damage of endothelial cells (EC), i.e., the components of endothelium, during stent implantation, could lead to severe complications, such as restenosis. To prevent restenosis, enhancements have been made to surface biocompatibility to accelerate the stent endothelialization process. Anodization on the Ni-Ti is a simple and efficient surface modification method to improve the biocompatibility of the Ni-Ti stent surfaces by enhancing the surface hydrophilicity, leading to an increase in the EC activities. The EC activity is known to be affected by the blood flow. Flow change by stent structure may result in EC dysfunctions, thereby leading to restenosis. It is thus essential to investigate the EC activities resulting from the anodization on the Ni-Ti surface under flow conditions. To study the influence of the endothelialization process on the Ni-Ti stent surface through anodization. The EC attachment and morphology on the anodized stent strut were observed under both with and without the flow conditions. A parallel plate flow chamber was designed to generate a constant wall shear stress (WSS) to study the flow effect on the EC behavior. The hydrophilicity of the Ni-Ti stent strut surface was enhanced by a TiO2 layer fabricated via anodization. The EC distribution on the surface of the anodized nitinol stent strut was observed after 24 h of static (without flow) and flow exposure (with flow) experiment. Under the static condition, the EC density on the surface of the anodized Ni-Ti stent strut was higher compared with the control. Under the flow condition, the enhancement of the EC density on the surface of the stent strut with anodization was reduced. The EC demonstrates a long and thin spindle-shaped morphology under the flow condition. Unlike the static condition, the EC is demonstrating a long and thin morphology in response to the flow under the flow condition. By improving the surface hydrophilicity, the anodization could enhance the EC migration onto the strut surface, and subsequently, accelerate the Ni-Ti stent endothelialization process. The improvement of the surface hydrophilicity is lower under the flow conditions when compared with the static conditions.

Investigation of topological regime in Bi2Se3 thin films through low-frequency electric noise

Topological insulators are considered new states of quantum matter that cannot be systematically related to conventional insulators and semiconductors. Among them, Bi2Se3 has attracted an increasing interest due to a simple surface band structure and due to a strong contribution of the surface to transport. While the dc electric transport properties have been extensively studied, intrinsic fluctuations and their effect on the surface conduction have received less attention. In order to better investigate these aspects, a detailed characterization of the low-frequency noise, also known as noise spectroscopy, has been made in Bi2Se3 thin films. The experimental results have been obtained for different samples thickness and geometry, in a temperature range from 300 down to 8 K, and as a function of dc bias current and gate voltage. While the observed spectral noise shows a typical thermal and shot noise part, an unusual reduction of the 1/f noise component is found, especially in the low-temperature region. A correlation of this behavior with structural and dc electric transport investigations suggests that it could be an indication of the occurrence of the topological regime. Flicker noise measurements, therefore, could be considered as a valid alternative technique to standard topological surface state spectroscopy.

Modelling the spatialisation of pesticide sales to monitor environmental policies in France

Environmental policy monitoring requires data with suitable spatial and temporal resolutions. We present a new method of spatialising pesticide sales in France to monitor environmental policies on a territorial scale. Data on pesticide sales in France are available yearly at a postal code resolution. Our spatialisation model combines parcel-scale land use data with information on pesticide types and applied doses, based on legal authorisations for pesticide use in France. We compared the performance of our new model with that of a simple surface fraction model in two distinct territories: Bourville (830 ha, Normandy), a small catchment composed of two small postal code fractions with available ground truth data about pesticide application, and Pleine-Fougères (12,007 ha, Britany), a larger area with a single postal code comprising seven municipalities with contrasting inter-municipal land uses and no ground truth information about pesticide application. For the Bourville site, due to homogeneous land use, the new model was no better than the simple model for global pesticide use, but it performed better when the results were analysed by crop type. For the Pleine-Fougères site, the new model was effective in distinguishing the use of pesticides by municipality, whereas the simple model was not. Our results demonstrate that our new model improves pesticide use quantification at a territorial level and can provide valid support for monitoring public policies regarding water quality and pesticide use over time and space.

On the challenge of sampling multiple nucleation pathways: A case study of heterogeneous ice nucleation on FCC (211) surface.

Heterogeneous ice nucleation is ubiquitous but its microscopic mechanisms can be extraordinarily complex even on a simple surface. Such complexity poses a challenge in modeling nucleation using advanced sampling methods. Here, we investigate heterogeneous ice nucleation on an FCC (211) surface by a forward flux sampling (FFS) method to understand how the complexity in nucleation pathways affects the accuracy of FFS. We first show the commonly adopted, size-based order parameter fails to describe heterogeneous ice nucleation on the FCC (211) surface. Inclusion of geometric anisotropy of ice nucleus as an additional descriptor is found to significantly improve the quality of the size-based order parameter for the current system. Subsequent application of this new order parameter in FFS identifies two competing ice nucleation pathways in the system: a primary-prism-planed (PPP) path and a secondary-prism-planed (SPP) path, both leading to the formation of hexagonal ice but with different crystalline orientations. Although the PPP pathway dominates ice nucleation on the FCC (211) surface, the occurrence of the less efficient SPP pathway, particularly its strong presence at the early stage of FFS, is found to yield a significant statistical uncertainty in the calculated FFS rate constant. We develop a two-path model that enables gaining a general, quantitative understanding of the impact of initial finite sampling on the reliability of FFS calculations in the presence of multiple nucleation pathways. Our study also suggests a few general strategies for improving the accuracy of FFS when exploring unknown but complex systems.

Two-dimensional glass/p-ATP/Ag NPs as multifunctional SERS substrates for label-free quantification of uric acid in sweat

Abnormal uric acid (UA) content in body fluids can fully reflect the status of metabolism and immunity in the body. We have developed a simple, efficient and label-free surface enhanced Raman scattering (SERS) method for UA detection. Briefly, p-aminothiophenol (p-ATP) was used as the internal standard molecule and linking molecule to prepare a glass/p-ATP/Ag NPs SERS substrate. The Raman characteristic peak of p-ATP at 1076 cm−1 can be used as an internal standard molecule to correct the signal fluctuation of UA detection. The results show that the SERS method owns a linear response with a ranging from 5 × 10-6 to 10-3 M of UA characteristic peak of both 693 cm−1 and 493 cm−1 with a determination coefficient (R2) of 0.9878 and 0.9649, respectively. Additionally, the SERS sensor has been further used for the analysis of UA in sweat and good recoveries were obtained for the sensing of sweat. We believe that the developed SERS substrate has potential for applications in healthcare monitoring.

Experimental investigation on wettability of refrigerants on laser-ablated surfaces

Due to the refrigerant's low surface tension, it is difficult to increase its static contact angle (SCA) on the surface. Existing studies all employed the method of low surface energy coating to increase the SCA of the refrigerant on the surface, but this method has the drawback of coating peeling. In this study, the SCAs of R134a and R1234ze(E) refrigerants on the surface were increased using a simple and reliable laser surface texturing technique. The results showed that the SCAs of R134a and R1234ze(E) on the polished surface were 6.2° and 6.4°, respectively, indicating that the surface was superhydrophilic. Immediately after laser ablation, the surface hydrophilicity was improved with SCA approaching 1° due to the increase in surface roughness and the oxidation effect of the surface. However, over time, the laser-ablated surface adsorbed substances containing hydrophobic C-C(H) groups, resulting in a gradual increase in SCA. The steady-state SCAs of R134a and R1234ze(E) on the laser-ablated surface were 12.2° and 12.7°, respectively, which were about twice the SCAs of the refrigerants on the polished surface. In terms of the increased percentage of SCA, the laser surface texturing technique is effective in increasing the hydrophobicity of the refrigerant on the surface.

Recombinant perlecan domain V covalently immobilized on silk biomaterials via plasma immersion ion implantation supports the formation of functional endothelium

Strategies to promote rapid formation of functional endothelium are required to maintain blood fluidity and regulate smooth muscle cell proliferation in synthetic vascular conduits. In this work, we explored the biofunctionalization of silk biomaterials with recombinantly expressed domain V of human perlecan (rDV) to promote endothelial cell interactions and the formation of functional endothelium. Perlecan is essential in vascular development and homeostasis and rDV has been shown to uniquely support endothelial cell, while inhibiting smooth muscle cell and platelet interactions, both key contributors of vascular graft failure. rDV was covalently immobilized on silk using plasma immersion ion implantation (PIII), a simple one-step surface treatment process which enables strong immobilization in the absence of chemical cross-linkers. rDV immobilization on surface-modified silk was assessed for amount, orientation, and bio-functionality in terms of endothelial cell interactions and functional endothelial layer formation. rDV immobilized on PIII-treated silk (rDV-PIII-silk) supported rapid endothelial cell adhesion, spreading, and proliferation to form functional endothelium, as evidenced by the expression of vinculin and VE-cadherin markers. Taken together, the results provide evidence for the potential of rDV-PIII-silk as a biomimetic vascular graft material.

The entorhinal-DG/CA3 pathway in the medial temporal lobe retains visual working memory of a simple surface feature.

Classic models consider working memory (WM) and long-term memory as distinct mental faculties that are supported by different neural mechanisms. Yet, there are significant parallels in the computation that both types of memory require. For instance, the representation of precise item-specific memory requires the separation of overlapping neural representations of similar information. This computation has been referred to as pattern separation, which can be mediated by the entorhinal-DG/CA3 pathway of the medial temporal lobe (MTL) in service of long-term episodic memory. However, although recent evidence has suggested that the MTL is involved in WM, the extent to which the entorhinal-DG/CA3 pathway supports precise item-specific WM has remained elusive. Here, we combine an established orientation WM task with high-resolution fMRI to test the hypothesis that the entorhinal-DG/CA3 pathway retains visual WM of a simple surface feature. Participants were retrospectively cued to retain one of the two studied orientation gratings during a brief delay period and then tried to reproduce the cued orientation as precisely as possible. By modeling the delay-period activity to reconstruct the retained WM content, we found that the anterior-lateral entorhinal cortex (aLEC) and the hippocampal DG/CA3 subfield both contain item-specific WM information that is associated with subsequent recall fidelity. Together, these results highlight the contribution of MTL circuitry to item-specific WM representation.

Electrochemical detection and quantification of catechol based on a simple and sensitive poly(riboflavin) modified carbon nanotube paste electrode

In the present research work, selective and sensitive catechol (CT) detection and quantification were shown in the presence of resorcinol (RS) in 0.2 M phosphate buffer (PB) solution by preparing a low-cost, simple, and green carbon nanotube paste electrode (CNTPE) surface activated with electropolymerized riboflavin (PRF). The morphological, conductivity, and electrochemical features of the modified electrode (PRFMCNTPE) and bare carbon nanotube paste electrode (BCNTPE) materials were analyzed using electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The PRF-activated electrode displays outstanding sensitivity, stability, selectivity, reproducibility, and repeatability for the redox feature of CT with improved electrochemical current and declined electrochemical potential compared to BCNTPE. The peak currents of CT are correlated to the different CT concentrations (CV method: 6.0–60.0 μM & DPV method: 0.5–7.0 μM), and the obtained detection limit (DL) and quantification limit (QL) are found to be 0.025 μM and 0.085 μM (CV method) and 0.0039 μM and 0.0132 μM (DPV method), respectively. The prepared PRFMCNTPE material was advantageous for the examination of CT in environmentally important tap water sample as a real-time application.

Enhanced Bacteriostatic Properties of Ti Alloys by Surface Nitriding

Surface nitriding has been widely used to improve the surface physicochemical properties of Ti alloys. However, the currently utilized surface nitriding methods, such as laser nitriding, typically require expensive and complicated instruments, which makes surface nitriding a less cost-effective process. Meanwhile, the antibacterial properties of surface-nitrided Ti alloy implants have not been evaluated. Thereafter, in this study, we were aiming to develop an effective, simple, and cost-effective surface nitriding strategy to enhance the antimicrobial properties of Ti alloy implants. The surface nitriding strategy was realized by wet-chemical etching and thermal treatment at controlled conditions. Results showed that the above surface modification treatments exerted significant effects on the phase composition and morphology of the newly formed phases on the surface of Ti samples. Crystalline TiN and TiO2 formed after treatments. Meanwhile, amorphous nitrides and oxynitride were also presented on the sample surfaces. The surface-modified Ti samples showed a bacterial inhibition effect compared with the non-treated Ti ones, and the bacterial inhibition effect was attributed to the released ammonia species from the surface of Ti samples. The surface modification strategy shows promise to improve the bacteriostatic property of Ti implants in dental and orthopedic fields.

Reconstruction of Low Dimensional Electronic States by Altering the Chemical Arrangement at the SrTiO3 Surface

AbstractDeveloping reliable methods for modulating the electronic structure of the 2D electron gas (2DEG) in SrTiO3 is crucial for utilizing its full potential and inducing novel properties. Herein, it is shown that relatively simple surface preparation reconstructs the 2DEG at the SrTiO3 (STO) surface, leading to a Lifshitz‐like transition. Combining experimental methods, such as angle‐resolved photoemission spectroscopy (ARPES) and X‐ray photoemission spectroscopy with ab initio calculations, that the modulation of the surface band structures can be effectively achieved via transforming the chemical composition at the atomic scale is found. In addition, ARPES experiments demonstrate that vacuum ultraviolet light can be efficiently employed to alter the band renormalization of the 2DEG system and control the electron‐phonon interaction . This study provides a robust and straightforward route to stabilize and tune the low‐dimensional electronic structure via the chemical degeneracy of the STO surface.

Hybrid extracellular vesicles for drug delivery

Extracellular vesicles (EVs) are expected to serve as interesting drug delivery vectors as they may offer unique and new properties for drug delivery. Their natural origin, protein and nucleic acid composition, and intrinsic pleiotropic therapeutic effects could enable new possibilities in the field of drug delivery. Here, we aimed to review the methods used to produce Hybrid EVs, a recently emerged type of EV-based vector made from both EVs and synthetic vectors to exploit their respective properties. Hybrid EV/synthetic objects can be obtained by incubation, electrostatic interactions, polyethylene glycol (PEG)-mediated fusion, co-extrusion, freeze-thawing, or simple EV surface modification, leading to different types of objects. We also opted to review the properties of these vectors, and specifically compared them with those of other drug delivery vectors. It has to be noticed that only a limited number of study report loading metrics that allow cross article comparison. Based on this critical analysis, we attempted to draw the pith and marrow from these relatively difficult-to-compare studies and integrate them into the more general context of opportunities in drug delivery and drug development, with a particular focus on oncology.

Inside Back Cover: Bandgap‐Engineered Germanene Nanosheets as an Efficient Photodynamic Agent for Cancer Therapy (Angew. Chem. Int. Ed. 12/2023)

Preparation of two-dimensional nanosheets with suitable band gap has been a challenge for their photodynamic applications. In their Research Article (DOI: 10.1002/anie.202215795), Min Ge, Jianlin Shi et al. report a cutting-edge regulatory approach to create H-terminated germanene with a bio-medically favorable direct band gap by a simple surface chemical modulation for bio-application in cancer photodynamic therapy.

Innenrücktitelbild: Bandgap‐Engineered Germanene Nanosheets as an Efficient Photodynamic Agent for Cancer Therapy (Angew. Chem. 12/2023)

The preparation of 2D nanosheets with suitable bandgaps for photodynamic applications has been a challenge. In their Research Article (e202215795), Han Lin, Jianlin Shi, and co-workers report a cutting-edge regulatory approach to create H-terminated germanene with a biomedically favorable direct bandgap by simple surface chemical modulation for application in cancer photodynamic therapy.

A comprehensive review on recent developments in materials and technological parameters for plasma transferred arc hardfacing process

Critical equipments of process and heavy engineering industries are prone to significant wear due to intense service conditions. Uneven and uncontrolled wear causes significant changes in dimensional and geometrical accuracies of the part surfaces, which adversely affect the parts’ functionality and service life of these parts. Shorter service life of these equipments and subsequent replacement of the same is one of the serious economic concerns. Hardfacing or hardsurfacing is comparatively an advanced metal deposition technology to deposit a hard and complex metal substrate layer on simple and softer base material surface. This process is gaining popularity at commercial level due to its unique capabilities to develop superior wear, corrosion, and impact resistance properties on worn out parts and offer huge economic advantage as substitute to costly replacement. The primarily aim of this study is to present a comprehensive review of the work done on the probable candidates for deposition materials, and summarize the influence of various process parameters on hard-faced surface characteristics. The critical issues like dilution, debonding, and residual stresses have been discussed for multi-layered hardfacing for iron-, nickel-, and cobalt-based hardfacing materials. The secondary aim of this study is to address practical issues such as selection of proper combination of base-substrate material, to understand the response characteristics of ‘plasma transferred arc hardfacing (PTAHF)’ process to minimize the de-bonding, dilution, and residual stresses and finally to improve quality of hardfacing practice.

Multi-surface and bounding surface models in hyperplasticity

We develop a series of models of the bounding surface type within the context of hyperplasticity theory, in which models are completely defined by the specification of two potentials. We first describe a simple bounding surface type model, based on an equivalent multi-surface model, but with the advantages that (a) only a single yield surface is required and (b) a smooth rather than piecewise linear response is achieved. We then generalise this model in a way that allows it to be calibrated against real data with similar facility to a multi-surface model. Each model is presented in a simple one dimensional form, with generalisations to two dimensions and to a full tensorial form. Finally we give an example of the newly developed model calibrated against a monotonic test, and present comparisons with one-way and two way cycling and two complex bi-directional tests.