Roughened Substrate Research Articles

Bond performance of fly ash-based geopolymer mortar in simulated concrete sewer substrate

Geopolymers have been extensively explored as a promising repair material for deteriorated Ordinary Portland Cement (OPC) concrete elements. However, knowledge of the adhesion performance of geopolymer to concrete substrates is limited. This study investigates the bond performance of low calcium fly ash geopolymer (FAGP) mortar and concrete for holistic acidic environmental conditions, such as in sewer rehabilitation. The bond evaluation was conducted by slant-shear test, performed at different substrate conditions, namely Rough-Dry, Rough-Saturated, Smooth-Dry and Smooth-Saturated, to simulate the in-service condition of a typical sewer pipe wall. The standard OPC repair mortar and a commercially available proprietary geopolymer repair product (P-GP) were evaluated and compared as controls to ascertain the viability of geopolymer for repair application. The shear bond strength of FAGP mortar was found to be in the order of 14 MPa, outperforming OPC and P-GP in all substrate conditions. Even though FAGP bond strength was insensitive to roughened substrate moisture levels, the synergistic effect of smoothness and moisture condition appeared detrimental. The testing of the prototype geopolymer-coated concrete pipe under line loading showed no sign of delamination at the bond plane. OPC and P-GP exhibited a distinct bond separation, which commenced at only 20 % of the ultimate load. The acid resistance and low permeability of FAGP mortar appeared to aid in preserving the repair bond.

Rational design of a membrane-coated cathode for selective electrochemical hydrogen evolution in chlorate electrolysis

The industrial chlorate process has traditionally used chromium(VI) as an electrolyte additive for high Faraday efficiency. However, due to its recognized toxicity and carcinogenic properties, the EU has regulated its usage, prompting the need for alternative approaches. In this study, we propose the adoption of a polymeric membrane-coated cathode (MCC) as a straightforward yet highly efficient solution to enhance the selectivity of the hydrogen evolution reaction (HER) in chlorate electrolysis. Proof-of-concept MCCs were fabricated by coating roughened titanium substrates with cation and anion exchange membrane layers, which function as selective barriers for anodic hypochlorite species. The study revealed that a thin membrane coating on the electrode surface effectively suppressed the permeation of anodic intermediates, without compromising the current density for HER. By optimizing the coating layer thickness and substrate surface properties of MCC, the chlorate electrolysis cell demonstrated an impressive Faradaic efficiency of up to 95% at a current density of 150 mA/cm², while maintaining exceptional stability. The outcome of this study can potentially advance the feasibility of industrial chlorate production in meeting regulatory requirements and effectively mitigating environmental consequences.

Repetitive nanoindenter scratch testing of polydopamine/polytetrafluoroethylene-based thin coatings

Repetitive nanoindenter scratch testing and scanning electron microscopy were used to evaluate the scratch resistance, deformation, and mechanisms of failure of polydopamine (PDA)/polytetrafluoroethylene (PTFE)-based coatings deposited on both polished and roughened 60NiTi substrates. PDA was used as an adhesive layer between the substrate and the PTFE top layer with and without 0.25 wt% graphite particles (GPs). The roughened substrate enabled mechanical interlocking with the coatings that prevented global delamination which occurred with the coatings on the polished substrate due to weak adhesion. The inclusion of GPs improved the coating cohesion and enabled the PDA/PTFE coating with GPs on the roughened substrate to compact into a more plowing-resistant layer with stronger interlocking with the substrate roughness. Therefore, the GP-containing coating deposited on a roughened substrate showed far superior performance, and it is a promising solid lubricant for tribological applications that involve repetitious sliding at high contact pressures, such as bearings and gears.

Effect of annealing temperature and ambience on roughened GaN substrate

Improving light extraction of GaN-on-GaN LEDs is still a challenge. This work attempted to address this issue by investigating the effect of temperature and ambience of annealing in obtaining high hexagonal pyramids density of roughened backside (N-face) GaN substrates for the light extraction improvement. Here, the GaN substrates were annealed prior to the roughening. The annealing temperature was varied at 600 °C and 700 °C in nitrogen, air, and oxygen ambiences. Results showed that the hexagonal pyramids density could be increased up to 4.3 × 1010 cm-2 by pre-annealing the GaN substrate in oxygen at 600 °C. In comparison to other ambiences, oxygen promoted more Ga–O compounds on the surface during the annealing. This enhanced the etching effect and hence, increased the hexagonal pyramids density. Meanwhile, with oxygen pre-annealing at 700 °C, the pyramids density for the GaN substrate was around 1.0 × 1010 cm-2. This result was almost comparable to the substrates annealed in other ambiences at 700 °C. The reason is that annealing at 700 °C was not only improved the GaN crystals, but also the Ga–O compounds. This turned the compounds to be in more stable structure and therefore, difficult to be dissolved by the etching. Moreover, the roughened GaN substrate with the highest pyramids density obtained in this work (through the 600 °C pre-annealing in oxygen) led to higher optical power of GaN based LED as compared its counterparts.

Surface-Enhanced Raman Spectroscopy Substrates: Plasmonic Metals to Graphene.

Surface-enhanced Raman spectroscopy (SERS), a marvel that uses surfaces to enhance conventional Raman signals, is proposed for a myriad of applications, such as diagnosis of diseases, pollutants, and many more. The substrates determine the SERS enhancement, and plasmonic metallic nanoparticles such as Au, Ag, and Cu have dominated the field. However, the last decades have failed to translate SERS prototypes into real-life applications. Irreproducibility on the SERS signal that stems from the roughened SERS substrates is the main causative factor for this observation. To mitigate irreproducibility several two-dimensional (2-D) substrates have been sought for use as possible alternatives. Application of 2-D graphene substrates in Raman renders graphene-enhanced Raman spectroscopy (GERS). This account used density functional theory (DFT) substantiated with experimental Raman to compare the enhancement capabilities of plasmonic Au nanoparticles (SERS), graphene substrate (GERS), and coupling of the two SERS and GERS substrates. The DFT also enabled the study of the SERS and GERS systems molecular orbital to gain insight into their mechanisms. The amalgamation of the SERS and GERS occurrence, i.e., graphene doped with plasmonic metallic substrates showed a pronounced enhancement and matched the Au-driven enhancement emanating from both electromagnetic and charge transfer SERS and GERS mechanisms.

Polydopamine Codoped BaTiO3-Functionalized Polyvinylidene Fluoride Coating as a Piezo-Biomaterial Platform for an Enhanced Cellular Response and Bioactivity.

For a number of clinical applications, Ti6Al4V implants with bioactive coatings are used. However, the deposition of a functional polymeric coating with desired physical properties, biocompatibility, and long-term stability remains largely unexplored. Among widely investigated synthetic biomaterials, polyvinylidene fluoride (PVDF) with β-polymorph and barium titanate (BaTiO3, BT) are considered as good examples of piezo-biopolymers and bioceramics, respectively. In this work, an adherent PVDF-based nanocomposite coating is deposited onto a Ti6Al4V substrate to explore the impact of its functional characteristics (piezoactivity) on cellular behavior and bioactivity (apatite growth and mineralized matrix formation). The precursor solution was prepared by physically grafting PVDF with polydopamine (pDOPA), forming mPVDF. Subsequently, mPVDF was reinforced with BaTiO3 nanoparticles in dimethylformamide/acetone solution, and the resulting nanocomposite (mPVDF-BT) was then spray-coated onto a roughened Ti6Al4V substrate using an airbrush at 140 °C under a pressure of 2 bar. The reproducibility of this simple yet effective processing approach to deposit chemically stable and adherent coatings was established. Remarkably, the modification with pDOPA and reinforcement with BaTiO3 nanoparticles resulted in an enhanced β-fraction of PVDF up to 96%. This nanocomposite encouraged cellular viability of preosteoblasts (∼158% at day 5) and characteristic spreading, in vitro. Our findings indicate that the mPVDF-BT coating facilitated faster nucleation and growth of the biomineralized apatite layer with ∼70% coverage within 3 days of incubation in the simulated body fluid. In addition, the coupling among surface polar energy (5.5 mN/m), fractional polarity (∼117%), roughness (8.7 μm), and fibrous morphology also endorsed better cellular behavior. Taken together, this coating deposition strategy will pave the pathway toward designing cell-instructive surface-modified Ti6Al4V biomaterials with tailored biomineralization and bioactivity properties for musculoskeletal reconstruction and regeneration applications.

Electrochemical fabrication of Ni‐P‐B ternary catalyst for hydrogen production in proton exchange membrane water electrolyzer

Hydrogen production via water electrolysis, which is crucial for addressing climate change, is limited due to the high cost and insufficient activity of the catalyst. Binary-nonmetal transition metal compounds are promising candidates for the hydrogen evolution reaction (HER) owing to the synergetic effect between metal and nonmetal elements. Herein, we report the facile fabrication of Ni phospho-boride catalysts and their compositional effects on HER activity. By controlling the deposition conditions, the elemental compositions were changed to modulate their electronic structures. Particularly, the HER intrinsic activity showed a volcano relationship based on the elemental P content. The optimized catalyst was prepared on a highly roughened substrate, which could be used as a cathode for a proton exchange membrane electrolyzer (PEMWE) single cell. A current density of 1.08 A cm−2 was obtained at a cell voltage of 2.0 V, which is comparable to state-of-the-art PEMWE single cell comprising nonnoble cathodes.

Improving backside (N-face) GaN substrate roughening by pre-annealing for GaN-on-GaN LED

This work attempted to improve roughening on backside (N-face) of GaN substrate by increasing the density of hexagonal pyramids for enhanced GaN-on-GaN LED performance. Prior to the roughening by ammonium hydroxide-based etching, the substrate was annealed in two different ambiences; air and oxygen. After the roughening, the hexagonal pyramids with a density of 4.3 × 1010 cm−2 were formed on the substrate with oxygen pre-annealing. For the substrate with air pre-annealing, the hexagonal pyramids density was 2.0 × 1010 cm−2. Meanwhile, the pyramids density for the roughened GaN substrate without pre-annealing was 0.5 × 1010 cm−2. The oxygen pre-annealing introduced more Ga–O compound on the surface. This increased the density of hexagonal pyramids, which resulted after the etching. The GaN-on-GaN LEDs grown on the roughened GaN substrates with pre-annealing (air and oxygen) emitted at 488 nm, while the LED on the roughened GaN substrate without pre-annealing at 510 nm. The optical power increased significantly when the LED grown on the roughened GaN substrate with the oxygen pre-annealing. Overall, this work revealed that the backside GaN roughening can be improved by oxygen pre-annealing, leading to enhance the GaN-on-GaN LED performance.

N-face GaN substrate roughening for improved performance GaN-on-GaN LED

Purpose This study aims to focus on roughening N-face (backside) GaN substrate prior to GaN-on-GaN light-emitting diode (LED) growth as an attempt to improve the LED performance. Design/methodology/approach The N-face of GaN substrate was roughened by three different etchants; ammonium hydroxide (NH4OH), a mixture of NH4OH and H2O2 (NH4OH: H2O2) and potassium hydroxide (KOH). Hexagonal pyramids were successfully formed on the surface when the substrate was subjected to the etching in all cases. Findings Under 30 min of etching, the highest density of pyramids was obtained by NH4OH: H2O2 etching, which was 5 × 109 cm–2. The density by KOH and NH4OH etchings was 3.6 × 109 and 5 × 108 cm–2, respectively. At standard operation of current density at 20 A/cm2, the optical power and external quantum efficiency of the LED on the roughened GaN substrate by NH4OH: H2O2 were 12.3 mW and 22%, respectively, which are higher than its counterparts. Originality/value This study demonstrated NH4OH: H2O2 is a new etchant for roughening the N-face GaN substrate. The results showed that such etchant increased the density of the pyramids on the N-face GaN substrate, which subsequently resulted in higher optical power and external quantum efficiency to the LED as compared to KOH and NH4OH.

The effect of coating thickness on the tribological properties of polydopamine/PTFE + graphite particle coatings on 60NiTi

Polydopamine (PDA)/polytetrafluoroethylene (PTFE) + 0.25 wt% graphite particle (GrP) coatings of three different thicknesses were deposited on roughened 60NiTi substrates. Their tribological properties were evaluated by coating durability, wear progression, and scratch tests. It was found that the thicker coatings have longer wear life, but the wear life was not proportional to the coating thickness. The coating thickness affected the transfer film and contact pressure and thus the coating durability. The coating wore rapidly to the coating-substrate interface and then wore at a very low wear rate. The thicker coatings had lower critical loads at which gross coating failure occurred.

Corrosion engineering derived Ga doped CoSe2 nanosheets intrinsically active for oxygen evolution reaction

The development of active and robust oxygen evolution reaction (OER) electrocatalysts in alkaline media is of great value for high-efficiency hydrogen production through electrochemical water electrolysis. Heteroatom-doping and defect-introduction are critical strategies in activating OER electrocatalysts. Herein, a combined magnetron sputtering, Co–Ga alloying, dealloying and selenization strategy was adopted to realize Ga-doped CoSe2 nanosheets with enriched oxygen vacancies supported on stainless steel mesh (SSM) for OER. The as-obtained L-CoSe2/SSM exhibits remarkable OER performances with an ultralow overpotential of 227 mV at 10 mA cm−2, and small Tafel slope of 49.15 mV dec−1 in 1 M KOH. In addition, the catalyst displays negligible activity decay after more than 25 h of continuous operation. The enhanced OER performances of the L-CoSe2/SSM can be rationalized by plentiful oxygen vacancies, Ga doping, unique roughened nanosheets structure and substrate (SSM). The findings provide promising and controllable synthetic strategy for low-cost CoSe2 based electrocatalyst toward practical applications of water electrolysis.

Wettability model for water-ethanol binary mixture droplet on roughened low-surface-energy solids

Wettability of a droplet on rough solid surface exhibits complex behavior compared with a droplet on smooth solid surface. On a hydrophilic / hydrophobic solid substrate, hydrophilicity / hydrophobicity of a droplet changes as the surface roughness of the solid substrate varies. This kind of wettability is mainly discussed on the basis of Wenzel and Cassi-Baxter models where the wettability of droplets on roughened surface is analyzed by the concept of roughness ratio and contact area fraction. However, in an actual situation, it is very difficult to quantify the structure of the roughened surface and the contact area between liquid and solid surface strictly. In the present study, wettability of water-ethanol binary mixture droplet on roughened low-surface-energy solid is experimentally investigated in order to understand the wetting behavior in wide range of surface tension of liquid. A simple morphological model to quantify the surface roughness and critical surface tension of roughened solid surface is proposed. In addition, analytical model to predict the wettability on roughened solid surface is developed on the basis of the concept of adsorption of liquid molecules at solid–liquid interface, which can be applied to wetting behavior on both hydrophilic and hydrophobic roughened solid substrates.

Polyaniline coating electrochemical properties improvement after roughened platinum substrate and its anti-wear performance study

In order to improve the electrochemical performance of the neural electrode the polyaniline coatings were modified on roughened Pt (PANI/rPt1) electrodes using electrochemical method. The roughness factor (fR up to 424) of Pt surfaces increased significantly through electrochemical roughening processing. PANI/rPt electrodes showed excellent interfacial properties. Specifically, about 5.6-fold increase in the charge density of PANI/rPt (fR = 424) was observed, while the interfacial impedance (103.5 Ω) was reduced by 50% compared to that of PANI coatings on the smooth Pt surfaces (PANI/sPt2). The results indicate the potential application of PANI/rPt as an efficient and stable future neural interface. In addition, the wear test shows that the coating did not fail during the wearing period and holds an excellent wear resistance ability.

Electrochemically treated graphite/poly(3,4-ethylenedioxythiophene)-carbon nanotubes electrode: facile preparation and remarkable enhancement in electrochemical performances

This work reports an approach to significantly improve the supercapacitive properties of poly(3,4-ethylenedioxythiophene)-carbon nanotubes (PEDOT-CNTs) hybrid electrodes. Specifically, a facile electrochemical treatment method is put forward to roughen graphite (G). After that, the electrochemically treated graphite (EG) acts as the substrate to load the PEDOT-CNTs composites by electrochemical co-deposition. The obtained EG/PEDOT-CNTs electrode shows substantially enhanced electrochemical performances with respect to G/PEDOT-CNTs electrode, caused by optimal electron transfer pathways between PEDOT-CNTs composite films and the roughened EG substrate. Here, the EG/PEDOT-CNTs electrode achieves a high specific capacitance of 278.7 F g−1 at 1 A g−1, higher than those of PEDOT based composite electrodes in various studies reported recently. This study demonstrates that the roughening treatment of the electrode substrate is an effective approach to substantially promote the supercapacitive properties of electrodes.

The Effect of Machined Surface Conditioning on the Coating Interface of High Velocity Oxygen Fuel (HVOF) Sprayed Coating

Roughening the substrate surface is essential for thermal sprayed coatings. In this regard, sandblasting has established itself as an easy to use surface conditioning procedure. The quality of the obtained roughness depends on the conditions of the sandblasting material, adjusted parameters, and the kind of the process execution (manual or mechanical). These preconditions limit the reproducibility of the roughness obtained. Sandblasting causes residual compressive stress and may also lead to the inclusion of sand particles and notches in the roughened surface, which affects the interfacial properties of the coating, as well as the flexural strength of the coated parts. The hardness of the roughened surface plays, thereby, an important role. However, in order to reliably avoid these effects, microfinishing can be used as an alternative to generate a homogenous roughened substrate surface, control the induced residual stresses, and increase the reproducibility. In addition, the roughened surface pattern can be produced during the chip forming process of the to-be-coated parts. The utilization of the appropriate combination of machining processes and parameters should lead to the required surface pattern and thus to an enhanced coating adhesion and flexural strength of the coated part. The induced residual stresses and the quality of the obtained surface roughness have a significant influence on the coating adhesion and the lifespan of the coated parts. This paper aims to analyze, as a first step, the effect of the turning and microfinishing on the surface conditioning of the bearing steel 100Cr6 (AISI 52100). The investigation concludes by comparing the microfinished with the sandblasted surfaces with regard to the interface to and the adhesion of the WC–Co high velocity oxygen fuel (HVOF) sprayed coatings on them. Surface conditioning plays a decisive role by the induced residual stresses and the elimination of adhesion defects.

Thermophoresis of gold nanorods from surface enhanced Raman scattering and real-time Rayleigh scattering in solution

Surface-enhanced Raman scattering (SERS) from gold and silver nanoparticles suspended in solution enables a more quantitative level of analysis relative to SERS from aggregated nanoparticles and roughened metal substrates.

THz SERS Observation of Benzenethiol Monolayers on Electrode Surfaces

Surface-selective vibrational spectroscopy is a powerful tool to study various interfacial phenomena such as electrochemical reactions at electrode/electrolyte interfaces. Among various spectroscopic methods, surface enhanced Raman scattering (SERS) is a promising method to conduct in-situ observation in IR- and THz-opaque media. According to recent technological advancements in fabrication of optical filters, elimination of Rayleigh scattering has become highly efficient. Thus, it is now expected that very low-frequency vibrations such as THz vibrations can be observed even in aqueous solutions [1]. Figure shows that an extramolecular vibration of benzenethiol monolayers with ultra-low frequency is indeed observable using this method. We will discuss charge transfer resonances at metal/molecule interfaces based on this low frequency vibration. Figure caption THz-SERS spectra of monolayers of benzenethiol derivatives on a roughened Au substrate Reference [1] M Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 2017, pp. 4236-4240. Figure 1

Making culverts great again. Efficacy of a common culvert remediation strategy across sympatric fish species

Culverts are instream structures that act as hydrological barriers to fish movement by altering water turbulence, increasing water velocities and disrupting connectivity. Hydrological barriers like culverts have led to the fragmentation and decline of freshwater fish populations worldwide. Culvert remediation strategies such as bed roughening have proved effective at increasing the likelihood of fish passage in a variety of fish species. However, little is known about whether culvert roughening is efficacious for Australian small bodied fishes and if so, whether bed roughening is comparably beneficial to all species that may utilise remediated culverts. This study assessed the effect of roughened bed substrates on the swimming performance and behaviour of four small bodied or juvenile Australian fishes (Hypseleotris compressa and Melanotaenia duboulayi, and juvenile Tandanus tandanus and Maccullochella peelii) that exist in sympatry over parts of their distribution. Results showed that bed roughening increased water turbulence and the size of low velocity regions within fluid flow and that all fish species displayed the same positive behavioural preferences for these zones. However, the effect of bed roughening on swimming endurance and traversability was found to only benefit Mel. duboulayi and Mac. peelii. Roughening decreased endurance and traversability in T. tandanus, and had no effect on performance in H. compressa. These data indicate that sympatric species may respond differently to culvert remediation actions, highlighting the need for a holistic approach to culvert remediation and a comprehensive understanding of all species’ requirements within the affected environment.

Structural behavior of double-lap shear adhesive joints with metal substrates under humid conditions

Structural adhesive bonding is very often used joining method in aerospace and automotive industry, but in civil engineering, especially in facade applications, semi-flexible or semi-rigid adhesives are still rarely used. The article is focused on experimental analyses of structural adhesive joints intended for facade applications (e.g. bonding of facade cladding elements to the supporting substructure). The experimental study contains a comparison of the structural behavior of two different adhesives in joints with aluminum or zinc-electroplated steel substrates with various surface pre-treatments. The main goal of the study is a comparison of the mechanical properties of joints exposed and unexposed to laboratory ageing conditions; immersion on demineralized water according to ETAG 002 (Guideline for European Technical Approval for Structural Sealant Glazing Kits). Water content in adhesive layer can change significantly its mechanical properties and adhesion of glue to the substrate. Ageing resistance of joint can be improved by durability increasing of the substrate. For this reason, two different substrate materials with various surface treatments (mechanical roughening, smooth surface, anodizing) were tested. Different adhesive resistance against humid conditions was observed depending on the substrate material and pre-treatment. STP polymer joints showed strength reduction by 30% after immersion for almost all substrates, while acrylate adhesive proved 20% strength reduction for roughened aluminum substrate and 60% strength reduction for zinc-electroplated steel substrate with a roughened surface. The zinc-electroplated steel substrate showed problematic adhesion in case of the acrylate adhesive both reference set of specimens and specimens exposed to laboratory ageing. The positive effect of roughening on adhesion and ageing resistance was clearly observed in the specimens bonded by the acrylate adhesive.

Enhancing surface immobilization of bioactive molecules via a silica nanoparticle based coating.

Surface modification is of significant interest in biomaterials, biosensors, and device biocompatibility. Immobilization of bioactive or biomimetic molecules is a common method of disguising a foreign body as host tissue to decrease the foreign body response (FBR) and/or increase device-tissue integration. For example, in neural interfacing devices, immobilization of L1, a neuron-specific adhesion molecule, has been shown to increase neuron adhesion and reduce inflammatory gliosis on and around the implants. However, the activity of modified surfaces is limited by the relatively low concentration of the immobilized component, in part due to the low surface area of flat surfaces available for modification. In this work, we demonstrate a novel method for increasing the device surface area by attaching a layer of thiolated silica nanoparticles (TNPs). This coating method results in an almost two-fold increase in the immobilized L1 protein. L1 immobilized nanotextured surfaces showed a 100% increase in neurite outgrowth than smooth L1 immobilized surfaces without increasing the adhesion of astrocytes in vitro. The increased bioactivity observed in the cell assay was determined to be mainly due to the higher protein surface density, not the increase in surface roughness. In addition, we tested immobilization of a superoxide dismutase mimic (SODm) on smooth and roughened substrates. The SODm immobilized rough surfaces demonstrated an increase of 145% in superoxide scavenging activity compared to chemically matched smooth surfaces. These results not only show promise in improving biomimetic coating for neural implants, but may also improve surface immobilization efficacy in other fields such as catalysts, protein purification, sensors, and tissue engineering devices.